5. Primary Prevention – Prevention of Skin Cancer

The following is a reference to the recommendation of the Radiation Protection Commission "Protection of Humans from the Hazards of Solar UV Radiation and UV Radiation in Solaria" [Strahlenschutzkommission et al. 2016].

Avoidance of excessive sun exposure is the most important sun protection measure and has the highest priority.
The level of potential UV radiation exposure depends on, among other things:

• Season
• Time of day
• Weather conditions (cloud thickness and cloud cover)
• Altitude (sea level, mountains)
• Reflection from the ground (earth, sand, snow, water)
• Shade

The strength of the solar radiation can usually be estimated well by looking at the sky. However, when the sky is cloudy, it is possible to underestimate the UV exposure, because even when there is a closed thin cloud cover, UV radiation penetrates through the clouds and is scattered by the clouds. In this case, the so-called UV index helps to assess the possible UV radiation exposure. It is determined by measurements and calculations and published by the weather service and other institutions in the media (internet, newspaper, television). Depending on the level of the UV index, various sun protection measures are recommended by the WHO.

If the UV index is not known, the so-called "shade rule" can be used to determine whether dangerous sun exposure is to be expected. The sun is higher than 45° above the horizon when the shadow is shorter than the object casting the shadow. In this case, strong UV radiation is to be expected. However, solar radiation can already contain high UV components at a lower position of the sun (about 35° - 40°).

The strongest solar radiation occurs at the highest sun position at midday when there is little cloud cover. About 50% of the total UV dose of a day occurs in the time window of two hours both before and after the sun's highest position. Therefore, it is recommended to avoid longer stays outdoors between 11:00 and 16:00 o'clock if possible, especially in the case of very strong solar radiation. Even before and after this time, strong UV exposure can occur under clear skies, so that even then suitable sun protection measures are recommended for longer stays in the sun. If possible, sports and leisure activities should be moved to the morning and evening hours if the weather is suitable.

It should be noted that the highest point of the sun within a time zone depends on the geographical longitude. In the east of Germany, the sun is highest in summer at 13:00 (Central European Summer Time), while in the west of Germany it is only around 13:40. In relation to the entire area of Central European Summer Time, for example, this results in a time window of the sun's highest point between 12:30 p.m. (Poland) and 2:30 p.m. (Spain). Therefore, the recommendation to avoid the midday sun (+/- two hours around the peak of the sun) should be adapted to local conditions, especially when travelling abroad.

The skin's own protection time depends on the respective skin type. In order to avoid overloading the skin with UV radiation and sunburns, the duration of stay in the sun should not exceed this self-protection time of the skin. Self-protection time is understood to be the maximum period of time during the course of a day for which the untanned skin can be exposed to the sun without getting a sunburn (however slight).

If a longer stay outdoors takes place in strong sunlight, the duration of the unprotected stay in the sun should be kept as short as possible in order to minimise the UV radiation dose. With regard to the protective measure "Seek Shade," it should be noted that not every type of shade reduces the UV radiation intensity to the same extent. UV radiation comes not only directly from the direction of the sun, but also indirectly from the environment, since solar UV radiation is scattered by water and air molecules (diffuse radiation). Therefore, the shading of direct solar radiation (e.g. by a sunshade) alone does not mean that UV radiation no longer reaches the skin and eyes, as the diffusely scattered UV radiation still reaches the body. The reduction of UV radiation varies depending on the type and extent of shading. The nature and orientation of the shading elements play a role. In this case, additional sun protection measures are necessary. If, in addition to direct solar radiation, the sky is also shaded over a large area (e.g. in deep urban canyons or in a dense forest), then the scattered proportion of solar UV radiation is lower and the shade is sufficient.

Avoiding Sunburns

As already described in Chapter 4.3.3 and the table "Influence of UV Exposure Pattern on the Relative Risk for Melanoma Development," a correlation between the occurrence of BCC (and presumably also of SCC), as well as melanoma, with sunburns can be established [34]; [353][354]. In addition, the prospective Nambour Skin Cancer study (1992-1996, follow-up to 2004) showed a strong association between BCC on the upper body and the number of reported sunburns. Study participants who had experienced more than 10 sunburns, compared with those without sunburns, had a more than doubled risk of upper body BCC (OR 2.49, 95% CI 1.04-5.99). The incidence of BCC on the head also increased with the number of sunburns (OR 1.79, 95 % CI 0.93-3.45 at > 10 sunburns) [355].

Slow Habituation to the Sun

In principle, it is always important to accustom the skin slowly to the sun. This is particularly important with increasing sun exposure in spring or during holidays with increased UV exposure. Accustoming can be done by repeated short stays in the sun, which are so short that no reddening of the skin occurs.

If it is not possible to avoid spending time outdoors in strong sunlight, the UV exposure of the skin should be reduced as far as possible by individual shielding from the sun's rays. This is done, for example, by suitable clothing which covers the skin as much as possible.

Suitable clothing is preferable to the use of sunscreen products as individual sun protection. Clothing absorbs UV radiation. The unit of measurement of absorption is the UV protection factor (UPF), which is comparable to the sun protection factor (SPF) of sunscreens. Simple T-shirts can have a UPF of 20 or more, which is usually sufficient for individual sun protection. More solid clothing and special UV-protective clothing may also have a UPF of 50, 80, or more. Unlike the SPF of sunscreens (see below), the UPF is immediate and actual for as long as the garment is worn. For very thin fabrics (e.g. shirts, blouses, mesh shirts, some swimwear), the UPF is less than 20 and may not be sufficient.

In addition to protecting the skin, protecting the eyes from solar radiation is of great importance, since UV radiation can also cause acute and chronic damage to and in the eye (see Chapter 4.3.3.1). 

Melanoma, basal cell carcinoma, and squamous cell carcinoma can also develop in the eye. Therefore, this has been included in the recommendations for the primary prevention of skin cancer. Suitable sunglasses are used to protect the eyes when exposed to strong sunlight. The suitability is given, if the sunglasses show the sign "UV400," offer sufficient protection against lateral UV radiation, and correspond to the standard DIN EN ISO 12312 for sunglasses. This standard defines five different glare categories (degree of darkening). Sunglasses in glare category 2 or 3 are sufficient for everyday wear. Sunglasses in glare category 4 are used for extreme conditions, e.g. on glaciers, but are not suitable for road traffic. Overall, care should be taken to ensure that sunglasses have adequate side protection.

Looking directly into the sun high in the sky can cause irreversible damage or even blindness in a very short time. This also applies to the use of sunglasses. Sunglasses are not suitable for observing the sun. Only with special sun filters with very high radiation absorption can solar eclipses, for example, be observed without danger. Only at sunrise and at sunset is the use of eye protection filters not necessary.

Regarding the protection of sunglasses, refers to the recommendation of the WHO [356].  In this, the use of sunglasses is recommended from a UV index value of UVI 3 or more. Furthermore, it is recommended that sunglasses be worn especially near water as well as in snow and high mountains. Background is besides the UV protection to avoid formation of skin tumours at the eyelids, the proven connection of acute damage by UV radiation, the acute keratitis, acute retinopathy, as well as the chronic damage such as pterygia, pinguecula, climatic drop keratopathy, cataract formation as well as ocular surface carcinoma (see section 4.3.3.1). A correlation between macular degeneration and UV radiation cannot be shown at present. However, the blue component of sunlight may possibly play a role here, which is more penetrating in young people with clear lenses. A weak data situation exists concerning the UV intensity from which the mentioned damages occur, so that the WHO recommendation must be reconsidered given new data.

The correct application of sunscreen products is of great importance. Incorrect application can greatly reduce the effect of sunscreens.

Sunscreens should be applied in a sufficiently thick layer. When determining the sun protection factors of sunscreens, an application layer of 2 mg/cm² is taken as a basis (see e.g. [367]).

To achieve the SPF indicated for a sunscreen product, an adult (approx. 1.5 - 2 m² skin) must use about 30 to 40 ml for the entire body. This is equivalent to about 1/5 of a standard 200ml bottle.

Sunscreen should be applied evenly and to all exposed areas of the skin. It is estimated that in practice often only one third to one fifth of the stated SPF is actually achieved, which leads to an overestimation of the protective effect. The application should be done before the beginning of the sun exposure and not only during the stay in the sun. Sweating and bathing will cause the sunscreen to come off the skin after some time. Therefore, waterproof sunscreen is preferable and application should be repeated at least every two hours. After bathing, the sunscreen must be reapplied. The lips should also be protected with a suitable product.

As the informative value of the sun protection factor for practical use is limited, the effectiveness of sunscreen products is now no longer described with numerical values but, in accordance with Recommendation 2006/647/EC of the EU Commission, verbally in four categories for different protection levels (low, medium, high, very high).

Sunscreens were originally developed to protect the skin during unavoidable stays in the sun to prevent major damage/sunburns. They absorb, scatter, and reflect UV radiation to a large extent, but not completely. They still allow some UV radiation to pass through to the skin, so the UV dose can accumulate there and contribute to long-term effects, such as the development of skin cancer.

Systematic reviews and meta-analyses of observational studies showed that no significant change in the incidence of malignant melanoma can be observed in users of sunscreens [364]; [368]. Other studies find evidence that sunscreen use may even be associated with an increased risk of melanoma [359]. This is thought to be due to a false sense of security due to sunscreen use and resulting prolonged exposure to the sun [357]. People who used creams with a higher SPF took longer sunbaths [369].

The use of so-called "self-tanning sunscreens," which contain psoralens (bergamot oil), appears to be associated with an even higher risk of melanoma development [359].

Gorham et al. [360] describe that in fair-skinned individuals the use of sunscreen may increase the risk for melanoma development. Overall, the authors do not find a significant increase in melanoma risk associated with sunscreens in their systematic review. However, when studies conducted in the northern hemisphere above 40 degrees latitude are pooled, the odds ratio is 1.6 (95% CI 1.3-1.9). The authors conclude that the use of sunscreens, which almost completely filter UVB radiation but transmit much of the UVA radiation, may contribute to melanoma risk in populations living above 40 degrees latitude [360].

Lin et al. [362] reported in a systematic review that regular use of sunscreen reduced the risk of SCC but did not reduce the risk of developing BCC [362]. After a follow-up of 10 years, a reduced risk of melanoma was found in the intervention group [361]. In subtropical areas, the development of solar keratoses can be reduced by the use of sunscreen [363].

A prospective cohort study within the Norwegian Women and Cancer Study (NOWAC) analysed participants' use of sunscreen at latitudes <45 degrees (i.e. closer to the north/south pole than the arithmetic mean between the equator and the north/south pole. In Europe, the northern 45th parallel is generally considered the northern boundary of southern France) [366]. 

The study included women aged 40-79 years who testified to having spent at least one week of vacation sunbathing in their lifetime in said regions (n=42,479). Endpoints represented sunscreen use, skin reactions, and cancer incidence. According to the results, users of sunscreens who had a history of sunburns have a higher risk of melanoma compared to non-users, while users of sunscreens without such a history have a lower risk. Non-users have a lower risk of melanoma compared to users of sunscreens with SPF < 15. However, use of sunscreens with SPF ≥ 15 results in an 18% reduction in melanoma incidence over a 10-year period compared with users of sunscreens with SPF < 15.

A case-control study [365] concluded that melanoma patients used sunscreens less frequently or not at all compared with a control group (use of sunscreens never/ infrequently: OR 12.28 (95% CI: 5.56-27.14, p<0.001); use of sunscreens always and repeatedly: OR 2.19 (95% CI: 1.23-3.91, p=0.01)); however, this does not allow the reverse conclusion that sunscreens reduce the risk of melanoma. According to this study, melanoma patients and controls mainly differ in the number of sunburns in childhood (six to ten sunburns in childhood/adolescence: OR 4.95 (95% CI: 2.29-10.71, p<0.001; >11 sunburns in childhood/adolescence: OR 25.52 (95 CI%: 12.16-53.54, p<0.001).

Need for Research

With regard to the use of sunscreens with exclusively mineral sun protection factors (such as zinc oxide or titanium dioxide) or chemical sun protection factors, no recommendation can be made due to the lack of a systematic literature review. The advantages and disadvantages of the respective sunscreens, especially with regard to the absorption of chemical agents (see e.g. [370]) as well as the question of a sufficient sun protection factor (and this especially for the application in children) must be reviewed and evaluated on the basis of evidence before a statement on this is possible. Additionally, it is essential to further investigate the relationship between melanoma risk and the use of sunscreens in order to clarify the question of a protective effect. Furthermore, application aids for the implementation of the dosage recommendations should be developed.

All publications report data or pooled data from cohort or case-control studies, meaning that the rate ratios reported here are measures of association. Evidence for a possible causal association includes: correct temporal association, dose-response association, consistency, and specificity of association.

A total of three systematic reviews and one cohort study not yet included in the systematic reviews were included.

The three systematic reviews included mostly the same studies. Almost exclusively case-control studies with a total of more than 11,000 melanoma cases were included.

Regarding the occurrence of malignant melanoma in "tanning bed users" compared to "non tanning bed users," the most recent review by Burgard (2018) reported an adjusted OR of 1.21 (95% CI: 1.08 – 1.36; 31 studies), representing an increased risk of MM occurrence in comparison. Colantonio (2014) reported an adjusted OR of 1.16 (95% CI: 1.05-1.28, 31 studies) and Boniol (2012) reported a relative risk of 1.20 (95% CI: 1.08-1.34; 27 studies; 25 and 24 studies already included in Burgard and Boniol, respectively). The weakness of Boniol's (2012) study is that the study quality of the included studies was not assessed and the included studies were only observational studies (case-control studies and cohort studies). A subgroup analysis of studies assessed as having low risk of bias (risk of bias according to the Newcastle Ottawa Scale (NOS): 67.7% of the 31 included studies scored less than four stars) was conducted by Burgard (2018), which found no association (OR 1.15 95% CI: 0.94 – 1.41). The subgroup analysis received a SIGN score of 2++. The weaknesses were the lack of interventional studies and serious limitations in the form of unobserved and unrecorded confounders. Subsequently, further studies with higher quality and adjustment for important confounders are needed. Colantonio (2014) classified six of the studies included here as having unclear bias risk and three as having high bias risk. Boniol (2012) had not conducted a quality/bias assessment.

Analyses were also conducted in all three systematic reviews on the influence of frequency of tanning bed use and age at first tanning bed visit (see Table "Study results on the association between tanning bed use and skin cancer risk").

Boniol (2012) included a total of 27 studies in the systematic review as mentioned above, Colantanio (2014) included 31 studies and Burgard (2018) also included 31 studies. The results are congruent – a statistically significant association was described regarding the occurrence of MM and an increased frequency of tanning bed visits. A non-statistically significant association was found for infrequent visits (e.g. < 10). A statistically significant association was reported between the incidence of MM and the proportion of those who visited the tanning bed for the first time at a young age (25 or 35 years cut-off). This was not the case in the older subgroup. 

In another prospective cohort study, Ghiasvand (2017) examined melanoma incidence in tanning bed users and reported a relative risk of 1.24 (adj 95% CI: 1.05-1.46) versus the comparison group. This result, as well as the result for the group of young tanning bed users, is in line with the results of the reviews. Due to the study design and the unclear potential for bias, the significance of the results is limited.

The following table summarizes the study results in total and by subgroup per review:

Wehner (2012) reported in their meta-analysis with 12 studies (cohort studies and case-control studies, n=80,661) an increased risk of developing epithelial tumours comparing "tanning bed users" vs. "never tanning bed users" (odds ratio [OR] SCC: 1.67 (95% CI: 1.29-2.17) and OR BCC: 1.29 (95% CI: 1.08-1.53), respectively).

A subgroup analysis for "intensive tanning bed use" revealed an OR of 1.5 (95% CI: 0.81-2.77) for the development of BCC, i.e., the risk of having developed BCC under "intensive tanning bed use" is not significantly increased.

For SCC, not enough data were available for a meta-analysis. A subgroup analysis for "onset of tanning bed use at a young age" showed an OR of 1.40 (95% CI: 1.29 - 1.52) for developing BCC. However, this was not significant when analysing SCC (OR 2.02; 95% CI: 0.70 - 5.86).

Karagas et al. (2014) identified 657 cases of BCC occurring between the ages of 25 and 50 years through the New Hampshire Skin Cancer Study database. Age- and sex-matched controls (n=452) were identified through the New Hampshire Department of Transportation. The authors reported an adjusted OR of 1.6 (95% CI: 1.3-2.1) comparing tanning bed users to the control group. A subgroup analysis clarified that the chance of "first tanning bed use at a young age (<20)" was two times greater (OR 95% CI: 1.4 – 3.0) among sufferers than the chance among controls.

Conducting more targeted studies for BCC and SCC is necessary.

Similar recommendations are made internationally: in general, WHO, ICNIRP, EUROSKIN, SSK, DKH, and ADP do not recommend the use of sunbeds. The WHO comes to the following conclusions in this respect: sunbed use is associated with an increased risk of skin cancer. This risk increases with the number of solarium visits and first-time use of a solarium at a young age. First-time use of tanning beds before the age of 35 increases the risk of melanoma by 60% (based on 13 studies, RR 1.87 (95% CI: 1.41-2.48) [373]. Each additional visit to a tanning bed in a year increases skin cancer risk by 1.8% (based on four studies, RR 1.018 (95% CI: 0.998-1.038)) [373]. First-time tanning bed use before the age of 25 increases the risk of squamous cell carcinoma by 102% (RR 2.02; 95% CI: 0.70-5.86) and the risk of basal cell carcinoma by 40% (RR: 1.40; 95% CI: 1.29-1.52) [376].

In Germany, a law for the protection of humans against non-ionizing radiation (NiSG) and a corresponding UV protection regulation (UVSV) have been in place since July 2009, regulating the operation and use of sunbeds. In particular, it was stipulated that young people under the age of 18 may not use sunbeds (§ 4, NiSG). The regulation stipulates, among other things, that people with skin type I and II should be advised not to use tanning beds and that qualified personnel must be available to check UV irradiation equipment and to contact users in order to fulfil the consultation and information obligations under the UVSV. According to the UVSV, since August 2012, old devices that do not comply with the EU requirement in force since 2007 of a limit on the total erythema-effective UV irradiance of 0.3 W/m² may no longer be operated – a value that corresponds to the erythema-effective UV irradiance at the equator at noon under a cloudless sky.

A meta-analysis of randomized clinical trials showed that the incidence of BCC and SCC of the skin was not reduced by taking antioxidant supplements (selenium, beta-carotene, vitamin A) [378]. Similarly, the development of AKs was also not reduced by beta-carotene intake [363].

No firm results are available from cohort or intervention studies suggesting a particular dietary pattern as a prevention strategy.

There is increased promotion in the lay press of taking antioxidant substances such as selenium, beta-carotene, and vitamin A as an additional means of UV protection. Beta-carotenes have no UV-protective effect [377]. A meta-analysis also showed no clinical evidence for the preventive effect of antioxidant supplements on skin cancer [378].

Caffeine-Containing Substances

There is evidence for protective effects of caffeine-containing foods on the development of skin cancer (primary studies: [379]; [380], meta-analysis: [381]). However, a recommendation for or against certain behaviours cannot be derived on the basis of the available data.

A meta-analysis [381] concludes that consumption of caffeinated coffee is associated with a reduced risk of melanoma, at least for individuals in the group with the highest coffee consumption (RR = 0.81, 95% CI: 0.68-0.97). The effect of caffeinated coffee was significant for women (RR = 0.76, 95% CI = 0.61-0.95) but not for men (RR = 1.11, 95% CI: 0.91-1.36). On a dose basis, the authors calculated a 4.5% reduced risk of MM (pooled RR = 0.955, 95% CI: 0.912-0.99) for one cup of coffee per day compared with non-users. However, the authors point out that possible chemopreventive effects of caffeinated coffee need further investigation. Also, the issue of confounders has not been adequately addressed.

From the Norwegian Women and Cancer (NOWAC) study, compared with low consumption of caffeinated coffee, there was a statistically significant negative association between low to moderate consumption of caffeinated coffee (> 1-3 cups/day, HR=0.80; 95% CI: 0.66-0.98) and moderate to high consumption (> 3 cups/day, HR=0.77; 95% CI: 0.61-0.97) and risk of malignant melanoma [379].

A prospective cohort study (1997-2007) [380] included participants (n=1,325) from a skin cancer study conducted in 1986 and resurveyed in 1992 and 1996. Participants were sent a questionnaire on caffeine consumption frequencies every six months (inclusion criterion: at least one completed questionnaire). Reported skin cancers were confirmed by histopathological findings. Whole-body skin examinations of all active participants were performed in 2007. The study describes a negative association between daily caffeine consumption (coffee and other caffeinated foods such as black tea, cola, chocolate) and BCC (RR=0.96 (95% CI: 0.87-1.05, p trend=0.20)), but only in individuals with previous skin cancer and mainly for individuals with high caffeine consumption (corresponding to an average of four cups of regular coffee) (RR=0.17 (95% CI: 0.57-0.97, p trend=0.025)). The results suggest that caffeine consumption may be an effective preventive measure in individuals diagnosed with skin cancer. This is especially true for individuals with high caffeine consumption (e.g., an average of four cups of regular coffee daily). However, the guideline group is unable to assess the risks potentially associated with heavy coffee consumption and therefore abstains from recommending.

Alcohol and Nicotine

No firm conclusions can be made about alcohol and nicotine in the context of skin cancer prevention.

A case-control study [382] investigated possible associations between cigarette consumption and the risk for BCC and SCC. An association was found in particular between cigarette consumption and SCC (OR=1.97; 95% CI: 1.19-3.26). In particular, among women the risk increased with the number of pack-years (OR at ≥ 20 pack-years = 3.00, 95% CI: 1.02-8.80). The study concludes that cigarette use is more strongly associated with SCC than with BCC, especially in women.

In the Woman‘s Health Initiative Observational Study (WHI OS) [383] it is postulated that higher alcohol consumption in post-menopausal white women is associated with increased risk of NMSC and MM. However, confounders were only collected at baseline. Recall bias and confounding are possible. High-risk behaviour alcohol consumption could influence other behaviours, e.g. lack of sun protection behaviour or tanning bed use.

A systematic review found ten studies on the association between cigarette consumption, melanoma risk, and mortality. Seven studies showed a negative association between cigarette use, melanoma risk, and mortality. Two studies showed a positive association, particularly in older individuals, and two studies found no association. The weaknesses of the review are, for example, that the association between socioeconomic status and lifestyle factors are not considered, although these are significant for explaining variance in behaviour [384].

Nicotinamide

The S3 guideline "Actinic Keratosis and Squamous Cell Carcinoma of the Skin" [385] cconsiders that nicotinamide can be used to prevent NMSC in patients with a history of NMSC or in organ transplant patients. The S2k guideline "Basal Cell Carcinoma" [386] recommends nicotinamide in patients predisposed to BCC for secondary prevention. Retinoids, on the other hand, should not be used for the prevention of BCC according to the BCC guideline, and further large-scale studies are considered desirable for COX2 inhibitors.

The guideline group does not see the use of nicotinamide as a means of primary prevention for the general population on the basis of the guidelines on SCC and BCC. No studies are available that allow conclusions to be drawn about the consequences of continuous administration of nicotinamide in the general population (including children and adolescents). The focus of primary prevention in the general population is on the risk reduction measures mentioned in the guideline.

Children's skin is very sensitive to the effects of solar radiation. This is especially true if they have a fair complexion. Sunburns in childhood increase the risk of developing skin cancer later. Therefore, very careful sun protection is necessary for children. As with adults, this includes first avoiding prolonged UV exposure, then wearing appropriate clothing that covers the body as completely as possible, suitable headgear and eye protection/sunglasses, and finally, as an additional measure, applying sunscreen to exposed areas of skin.

Gallagher et al. [391] showed in a randomized controlled trial that the number of nevi in children with fair skin (statistically significant in children with freckles), can be decreased by extensive use of sunscreen.

The systematic review by de Maleissye et al. [392] indicated that there is no evidence to date to support a protective effect of sunscreen on melanocytic nevi development in children. The included epidemiological studies were not homogeneous with respect to the age of the children and, moreover, different methods of counting melanocytic nevi were used. Thus, the study concludes that the assessment of the effect of sunscreens under real conditions is difficult and further studies with a uniform, standardized protocol have to be performed in order to be able to draw a conclusion.

Ulrich et al. [393] 

onducted a prospective study over two years with 120 organ transplanted patients. The study group received sunscreen in addition to information on sun protection; the control group received information material only. It was shown that in immunosuppressed recipients after organ transplantation, the regular application of sunscreen – as part of a consistent protection against UV radiation – protects against the development of further actinic keratoses, invasive SCC, and, to a lesser degree, also against BCC.

The above recommendation is in line with the international KDIGO guidelines for the care of renal transplant recipients, which recommend consistent, intensive UV protection, regular self-examinations, and annual whole-body examinations by a dermatologist for all transplant recipients [394].

For the risk of low vitamin D levels due to consistent UV protection in immunosuppressed individuals, see the following chapter, Chapter 5.1.3.

Vitamin D plays an important role in calcium balance and bone metabolism.

Sun protection measures reduce cutaneous vitamin D synthesis. Consistent sun protection may promote vitamin D deficiency in certain groups of individuals [395].

Srikanth et al. [396] found an inverse association between skin cancer and fractures: older individuals with a fracture were less likely to have NMSC, which was interpreted as lower cumulative lifetime sun exposure. Avoiding sun exposure may have adverse long-term consequences for future bone health. A review reported inconsistent studies on the reduction of fractures by administration of calcium and vitamin D [395]. However, the analysis showed a reduction in falls in the elderly with the administration of vitamin D.

Ulrich et al. [393] found no differences in vitamin D levels after 24 months in organ transplant recipients who practiced maximal sun protection compared with the control group. 

Nevertheless, they recommend that especially in risk groups (immunosuppressed, transplanted, etc.) who practice intensive sun protection, the vitamin D level should be checked and vitamin D should be substituted if necessary.

In a prospective cohort study, the 25(OH)D level was found to be higher in children with fair phenotype (fair skin, sunburn spots, often sunburned), compared to children with darker phenotype, although the former were more likely to use sunscreen and wear protective clothing according to their parents. The authors conclude that vitamin D synthesis in low-pigmented skin at northern latitudes is not completely suppressed by use of sunscreen or clothing. The study's validity is limited by the fact that children were studied in the 1990s, i.e., at times when awareness about adequate sun protection (e.g., in terms of sufficient amount of sunscreen) may have been less pronounced. In addition, some variables, e.g. 25(OH)D level, were determined only once per child [397].

Lindquist et al. [398]; [399] 

examine associations between sun exposure behaviours and all-cause mortality in a cohort study. They conclude that avoidance of sun exposure (never sunbathing, either on holiday or in summer, and never visiting solariums) is a risk factor for all-cause mortality in countries with low UV intensity. They speculate that the effect is due to vitamin D deficiency. However, vitamin D levels were not studied, nor were individual sun protection behaviours interrogated. Conclusions on a causal relationship between sun exposure behaviour and total mortality are not possible on the basis of the analyses.

Within the framework of an interdisciplinary scientific discourse initiated by the BfS and the UV Protection Alliance to harmonize hitherto contradictory recommendations regarding UV exposure for the formation of the body's own vitamin D, a consensual recommendation on UV radiation and vitamin D was developed [400]. In particular, the following recommendations were made:

• According to current findings, for sufficient vitamin D synthesis it is sufficient to expose the face, hands, and arms uncovered and without sunscreen two to three times per week to half of the minimum sunburn-effective UV dose (0.5 MED), i.e., half of the time in which one would otherwise get a sunburn without protection. For people with skin type II, for example, this means an exposure time of about 12 minutes at high sunburn-effective UV radiation intensities (UV index 7).
• Sunburn should always be avoided.
• UV protection measures should be taken for longer stays in the sun.
• The UV index (UVI) is recommended as a guide to the UV irradiance that causes sunburn and when UV protection measures should be taken. The UV index is a globally uniform measure of the highest possible sunburn-effective UV irradiance on a given day. The individual UVI values are assigned recommendations for the fair-skinned population regarding the UV protection measures to be taken.
• In the case of infants, children, and adolescents, particular care should be taken to avoid high levels of UV exposure and sunburns, because especially in childhood and adolescence, high levels of UV exposure and sunburns increase the risk of developing skin cancer later on.
• Infants should not be exposed to direct sunlight.
• Strong, non-medically controlled UV irradiation (sun or solarium) for the purpose of vitamin D formation, self-therapy of a vitamin D deficiency, or tanning is strongly discouraged.
• A vitamin D deficiency can only be diagnosed and treated by a doctor. Supplementation or medication with vitamin D preparations should be carried out under medical supervision. Infants and small children up to the second experienced early summer should receive vitamin D preparations.

Moderate exposure to UV radiation and high vitamin D levels may have a protective effect on the initiation and development of various cancers, including malignant melanoma. However, the available evidence regarding an association between overall cancer risk and vitamin D supply is insufficient.

One review addressed the question of whether sun exposure has a protective effect on the development of other cancers. It is possible that there were protective effects of sun exposure on the development of breast and prostate cancer. However, the studies were inconclusive; no association was found for the other cancers 

[401].

Tuohimaa et al. [402] showed in a historical cohort study that individuals with skin cancer (all types) had an increased risk of another primary cancer. Individuals who lived in sunnier latitudes had a slightly lower risk of a second tumour, which was attributed to a possible protective effect of vitamin D.

A review paper by Krause [403] compiled studies indicating a protective effect of sun exposure on colon and breast cancer. The authors also conclude that high levels of vitamin D appear to be a protective factor for cancer. The optimal UV exposure, the target level of circulating vitamin D, and whether vitamin D is the only way is not conclusively understood. Due to study deficiencies, the results have limited validity.

Schwalfenberg [395] cited studies in a review indicating a protective effect of vitamin D on heart disease and certain cancers. However, the review was methodologically flawed.

Using various ecological studies, WHO [International Agency for Research on Cancer (IARC). et al. 2008] examined whether there is a causal relationship between vitamin D levels and cancer risk. The results indicate an increased risk of colorectal cancer and colorectal adenoma with low vitamin D levels. Other studies again found no effect on the incidence of colorectal and breast cancer. This apparent contradiction between observational studies can be attributed to several factors, such as the use of low doses or an additional interaction with hormone therapy within the study. Epidemiological data suggest that vitamin D levels influence cancer progression and thus cancer mortality, and rather influence cancer incidence less.

Even the DGE  [Linseisen, J. et al. 2011] could not find consistent and clear results based on various meta-analyses on the relationship between vitamin D intake and the risk of different types of cancer. A conclusion cannot be drawn due to the inconsistency of the available results. The evidence regarding the association between individual cancer types or overall cancer risk and vitamin D intake is insufficient.

Lucas et al. [Lucas, Robyn M et al. 2007] found an association between vitamin D deficiency and increased risk of disease. Observational studies indicate an increased risk of colorectal cancer attributable to low vitamin D intake. No further conclusions could be drawn regarding other cancers, as either no results were available or the results already available were inconsistent.

Due to this inconsistent data situation, this S3 guideline follows the consensus recommendation on "UV Exposure for the Formation of Endogenous Vitamin D" of the scientific authorities, professional societies, and professional associations of radiation protection, health, risk assessment, medicine, and nutritional sciences (https://www.bfs.de/DE/themen/opt/uv/wirkung/akut/empfehlung-vitamin-d.html).

A gender-specific difference in sun exposure is shown in several studies. Women are more likely to seek shade for protection compared to men. In addition, sunscreen is used more by women, with a Norwegian study indicating a decrease in sunscreen use by women.

• Men and women differ in their sun protection behaviors, with women more likely to protect themselves from severe UV exposure. The extent of the gender differences differs for different sun protection-related behaviours.

Ghiasvand et al. [407] used data from the population-based Norwegian Woman and Cancer Study (NOWAC) to investigate changes in the sun protection behaviour of Norwegian women aged 41 to 75 years over the period 1997 to 2007. It was found that the use of sun protection products among Norwegian women increases over the years, but this is not accompanied by a reduction in the number of sunburns.

The cross-sectional study by Haluza et al. [404], which is representative for the population of Austria, showed that women protect themselves more from the sun overall compared to men. They used sunscreen more often, avoided the midday sun, sought out shade, and wore sunglasses (each p ≤ 0.001). Men were more likely to wear hats to protect themselves from the sun compared to women.

The study by Antonov et al. [405] showed a statistical difference in sunscreen use. Of the men, 15%, and of the women, 11%, had never used sunscreen in their lives (p=0.04).

A study conducted in Sweden on the sun protection behaviour of skin cancer patients (as intervention group) and patients with seborrheic keratosis (as control group) highlighted gender differences. Frequent sunbathing is more common for women (p<0.05), as is the use of sunscreen (p<0.001). Additionally, women were more likely than men to report seeking shade for sun protection (p<0.001). Use of tanning beds was more common among women [408].

The study by Blashill and Safren [409] examined the association between sun protection behaviours and sexual orientation among men aged 16 and 29 in the United States. Men belonging to a sexual minority (bisexual, homosexual) were significantly more likely to use tanning beds (27%) than heterosexual men (8.6%, p=0.002). They also tanned more often in the sun (22.3% vs. 14.5%, p=0.26). Between 70.5% and 75.9% of the men surveyed reported not using sunscreen.

Childhood and adolescence are critical periods for reducing the risk of skin cancer. Sun protection measures are of particular importance at this stage of life. Studies for the general population have already provided evidence that younger population groups in particular are intensively exposed to the sun.

• Although physical sun protection measures (exposure avoidance, textiles) are particularly recommended, sunscreens are the sunscreen of choice for children and adolescents, along with hats for young children.

Ackermann et al. [410] studied the sun protection behaviours of fifth, eighth, and eleventh grade students with mean ages of nine, eleven, and 15 years. A total of 1,154 students participated in the questionnaire survey. Of the students, 60.2% reported having suffered at least one sunburn. Two sunburns were reported by 30.1% of the students, and 11.2% reported at least three sunburns. In the previous year of the survey, 43.2% of students had a sunburn. Sunburns occurred in association with aquatic activities (50.3%), other sports activities (23.8%), and non-sports activities (25.9%). Half of the children reported that they had used sunscreen. Not having used sunscreen was the cause of sunburn in 26% of the children. Five percent would have stayed in the shade. In general, 69.2% of children reported using sunscreen regularly during the summer. Of these, two-thirds applied sunscreen repeatedly during sun exposure. Explicitly after swimming, sunscreens were reapplied by 55%. In winter, 39.5% of children regularly used sunscreen for sports activities. In addition, almost 90% of older students used a sun protection factor of 20 or higher. Shade is sought out by 32.8% of students when possible. Of students in grades eight and eleven, 31.5% reported wearing long-sleeved tops for protection from the sun.

An observational study by McNoe and Reeder [411] examined the sun protection behaviours of 1,225 13- to 18-year-old students during school athletic activities. Observations took place on days with a UV index greater than seven. Tops with an arm length longer than the elbows were worn by 19% of the students. Pants longer than knee length were worn by 21.4%. Sun protective hats were worn by 3.4% and sunglasses by 1.7% of students. Sunscreen was provided at five of ten events and shade was carefully provided in four. Shade was not generally available to students.

Basch et al. [412] examined the trend pattern for sunscreen and tanning bed use among high school students in the United States from 2001 to 2011 using data from the Youth Risk Behaviour Surveillance System (YRBSS). A reduction in sunscreen use among surveyed students from 67.7% (2001) to 56.1% (2011) was observed. In 2009, 15.6% of the respondents reported using tanning beds. In 2011, the figure was 13.3%. Fair-skinned females accounted for the largest proportion (37.4% in 2009, 29.3% in 2011). The prevalence of tanning bed use increased with increasing age of the respondents.

Dobbinson et al. [413] conducted telephone interviews with 1,140 parents of children aged zero to eleven years to assess their sun protection behaviour. On the weekend prior to the interview, 73% of the children were outside during the time of highest UV radiation. Sunscreen was used as a sun protection measure by 58% and hats by 64% of the children. Fourty-two percent of the children wore a sun protection hat. A wide brimmed hat was worn by 33% of the children and/or a hat with a neck covering was worn by 20% of the children. Two sun protection measures were reported for 61% of the children. Three or more sun protection measures were used by 29% of the children.

The prospective follow-up study by Dusza et al. [414] examined the sun protection behaviours of 360 children aged ten to 14 years. At baseline, 52.5% of students reported having experienced at least one summer sunburn. Liking tanned skin was reported by 53% of the students surveyed at baseline. After three years, this percentage increased to 66% (p<0.001). In addition, more children spent time in the sun tanning (21.8% vs. 39.8%, p<0.001). At baseline, 50% of children reported using sunscreen when outdoors for at least six hours; this was 25% at follow-up (p<0.001). The odds ratio for girls to use sunscreen frequently or always was 0.4 and for boys, 0.3.

In Switzerland, 887 students aged eight to 17 years in grades three, six, and nine were surveyed about their sun protection behaviours. More than half of the students (56.3%) reported having experienced sunburn in the previous year of the survey. Most students experienced sunburn related to aquatic activities (52.3%), 19.6% while sunbathing, 15.2% during other outdoor activities, 4.8% during winter sports, and 1% while working outdoors. On sunny summer days, 36.3% of the students surveyed almost always used sunscreen, 19.4% often, 24.9% sometimes, and 18.2% rarely to never. Boys were less likely to use sunscreen compared to girls. This also affected sixth and ninth graders compared to third graders, dark-skinned students compared to light-skinned students, and students whose parents had an education or no vocational degree compared to students whose parents had a higher education. Nearly half (49.3%) of the sixth and ninth graders surveyed applied sunscreen once in the morning. Sunscreen was used multiple times a day by 34.9% of the students. Girls were significantly more likely than boys to repeat sunscreen application (44.2% vs. 24.3%; p<0.0001) and light-skinned children and adolescents were more likely than those with darker skin (50.5% vs. 23.8%, p=0.006). After swimming, 43.7% of students reapplied sunscreen. Students used sunscreen with an SPF greater than/equal to 20 at a rate of 56.3%. Shade was sought by 32.2% of students when possible. When temperatures were uncomfortably high, 66.1% went to the shade. A shoulder-covering top was worn by 49.9% of the respondents on sunny summer days [415].

• Skin cancer patients show better sun protection behavior than comparison groups.

In a case-control study, Falk et al. [408] investigated sun exposure and protection behaviour of 55- to 69-year-old skin cancer patients compared to patients with seborrheic keratosis. Patients with a history of skin cancer were significantly less likely to go out in the sun to get a tan (p<0.01). They also protected themselves from the sun to a greater extent by seeking shade (p<0.001) and using sunscreen (p<0.001). Being more careful in the sun was reported by 77.9% of skin cancer patients. In comparison, 20.5% of patients had not changed their self-reported behaviour in the sun and 1.6% were less cautious.

• Knowledge about an increased risk of skin cancer and the implementation of protective behaviors are in need of improvement among organ transplant recipients.

Recipients of donor organs are particularly at risk for developing skin cancer due to long-term use of immunosuppressants. In the study by Vural et al. [416], 70 organ transplant recipients were interviewed about their knowledge of the increased risk of skin cancer for transplant recipients and their sun exposure behaviours. Forty-eight organ recipients (68.6%) reported being informed about the importance of avoiding sun exposure. That exposure to UV radiation can have dangerous consequences was known by 38 patients (54.3%). The causal relationship between skin cancer and UV radiation was known by 28 of the respondents (40%). Of organ transplant patients, 44.3% could not recall being informed about sun protection measures by clinical staff, while 55.7% of the respondents were educated about protective measures by dermatologists and/or nurses; 42.9% of patients had their skin examined by a dermatologist at least once after organ transplantation, and 14.3% of transplant recipients saw a dermatologist regularly (once or twice a year). Before organ transplantation, three patients had used sunscreen irregularly (only when vacationing in sunny areas). After transplantation, 25 patients started using sunscreen, so 28 patients reported using sunscreen. Eighteen patients reported using sunscreen only on sunny days or holidays. Other sun protection measures, such as hats, sunglasses, or long-sleeved tops, were used by 19 patients. Eight patients used all types of sun protective clothing when outside.

• For beachgoers, sun protection measures are very much focused on the use of sunscreen. Other possible measures (clothing, seeking shade) are hardly used.

Heerfordt, Philipsen, and Wulf [417] investigated the sun exposure behaviour of beach users in Denmark using webcam photos. During the period July 2015 to October 2015, a total of eleven days were designated as beach days. These are characterized by a daily average temperature of at least 20°C and at least ten hours of sunshine. A total of 2,259 beach users were observed on these eleven days. Of these, 26% wore clothing that covered more than 20% of the body surface area. Forty-six percent of beachgoers were present during the period from 12:00 to 15:00. The number of beachgoers peaked at 3:00 pm on weekend days and at 4:00 pm on workdays. At 1:00 pm, the minimum of 10% of people wearing clothing covering more than 20% of the body surface was observed. The average sun exposure time was 142 minutes at noon.

The interview survey by Cercato et al. [418] examined the sun protection behaviours of Spanish-speaking beachgoers. A total of 630 individuals were interviewed, who were predominantly female (62%) and had an average age of 30 years. Voluntarily exposing themselves to the sun frequently was reported by 80% of beachgoers. Seventy-six percent said they did so at the beach, 35% when playing sports, 29% in the mountains, and 22% in the pool. Sunscreen was used frequently (often/always) by 79.1% of beachgoers. Frequently using a sunscreen with a high SPF was reported by 81.2% of respondents. Using sunscreen with a high SPF throughout the day was often/always done by 62.3% of the respondents. Of beach goers, 76.4% apply sunscreen right at the beginning of sun exposure, 17.7% apply sunscreen 20 minutes before exposure, and 5.8% apply sunscreen only during exposure. Repeated application of sunscreen was frequent by 53.2% of beachgoers. With the exception of sunscreen, other sun protection measures are rarely used. Only 39.6% of respondents often or always seek shade during midday. A hat is worn often/always by 21.6% of beachgoers. T-shirts are worn frequently by 18.7% of interviewees. Sunglasses are often/always used by 49.5% of the interviewees.

Buller and Borland [442] studied 24 sun safety programs for children under 14 years of age. Short-term interventions such as individual lessons or visits to information days ("sun safety health fair") were suitable for improving knowledge about sun protection but had little influence on attitudes and behaviour. More effective were more intensive interventions lasting several days to several weeks, combining lecture series, information materials, workbooks, and others [442].

Dietrich et al. [443] reported on a two-year multicomponent program "SunSafe," which involved schools, kindergartens, doctors' offices, and recreational facilities in several communities. Children's sun protection behaviour was successfully promoted. This effect was reinforced by a second, less intensive refresher campaign [443].

Programmes that are comparatively successful in influencing behaviour, such as "Kidskin" [446] or "SunSafe" [443] and the two-year intervention "Sun Protection Is Fun" [437], are designed for the longer term. They combine different components, e.g. age-specific curricula, training sessions for teachers and beach lifeguards, information and training materials, posters, computer-based teaching modules, etc., and involve parents and other caregivers [444].

Weinstock et al. demonstrate moderate but sustained positive effects of a two-year multicomponent intervention involving informational materials, sunscreen, personal sun sensitivity testing, and written and verbal feedback among beachgoers. Reported sun protection behaviour improved in the intervention group compared with a control group, with the most pronounced effect in the 16-24 year age group [445].

Providing parents of young children with information material on a one-off basis does not appear to be sufficient to significantly influence sun protection behaviour, even when combined with provision of free sun cream [447]. An intervention limited to swimming lessons for primary school children, consisting of three to five minute lessons before swimming lessons combined with information material for home use, was also not likely to influence sun protection behaviour and tanning [448].

Therefore, special attention needs to be paid to strategies that produce the most sustainable behaviour change possible. From the available studies, "the" successful intervention strategy cannot be derived. The approaches and methods are too diverse for this. The share of individual components in the overall success of multi-component campaigns cannot be determined. There is also often a lack of evidence on the sustainability of observed effects and on transferability to German conditions. Nevertheless, some basic recommendations can be made.

The studies provide evidence that a theoretical foundation of programme concepts is important and useful. According to Garside et al. [449], who conducted a systematic review of qualitative studies, the elements of the health belief model in particular provide a coherent theoretical framework underlying many interventions, from which the barriers to information uptake about protective behaviour for the prevention of skin cancer can be derived. In addition, the model provides starting points for message design. For example, lack of knowledge, low risk perception, or the perception of sun tanning as healthy and attractive are important barriers to sun protection behaviour that can be addressed in campaigns [449]. Also, Glanz et al. [450] ncluded constructs such as risk perception, cost and benefit trade-offs of behaviour change, actionable knowledge and skills, and social norms as mediating variables derived from the health belief model and social cognitive theory to measure the effectiveness of personalized feedback [450].

Knowledge about the risks of UV radiation and knowledge about how to protect oneself are a necessary prerequisite for appropriate sun protection behaviour, but not sufficient for consistent translation into practical action [442]; [449]; [388].

In a web-based intervention, White et al. [452] present a one-time web- and theory-based intervention based on changes in psychosocial variables as well as information on proper UV-protective behaviour that is shown to be beneficial over a control group in which only UV-protective information was communicated.
 
Communication Channels

There is evidence in the literature that multiple as well as multimedia targeting of adults leads to better effects. For example, several studies have shown that multiple delivery leads to an increase in sun protection knowledge, self-efficacy in sun protection use, and sun avoidance. These effects were significantly different from the results of the respective control group [450] ; [455]; [460]. In addition, multimedia communication (e.g. videos) appears to be superior in effectiveness to purely text-based communication [461]. However, setting up a multimedia information booth with a touch screen at central contact points (city pharmacy, library, health centre) did not achieve improvements in knowledge, attitude, and behaviour [456]. However, there is no evidence for the general superiority of pictures over text in communication [462]. Boer et al. [457] 

showed that when educating people about skin cancer through slogans and through advertisements, both additional text and additional images increased knowledge about sun protection measures.

It is already true for individual means of communication such as advertisements that positive interaction effects can be demonstrated by a combined use of images and text modules with young adults in comparison to such advertisements in which only images or only text elements are used in addition to a slogan and logo. This can increase knowledge about the consequences of overexposure to the sun and improve the perception of the benefits of sun protection behaviour. At the same time, such ads with text-image combinations are perceived as more attractive and reflection on the ad is intensified [457]. 

However, when evaluating these findings, the limited external validity of the experiment should be considered in view of the laboratory situation and the large number of ads presented to the subjects for evaluation, as well as signs of a saturation effect ("ceiling effect") in view of the pronounced perception of the benefits of the protective behaviour even in the control group.

With regard to education and training programs, the studies considered here also indicate that, compared to the presentation of information via only one sensory channel without the possibility of selection and feedback by the recipient, communicative address via several sensory channels (text, graphics/photo, moving image/animation) as well as additional human-computer interaction in the training situation increase the probability of a more profound examination or higher processing depth of the information and thus the mediation performance. In addition, media and interpersonal forms of address should be combined, as this increases communication performance.

Repeated multimedia health education with animations, photos, and short information in clinical settings leads to better knowledge about melanoma and improved sun protection behaviour in at-risk individuals [459]. For adolescents, two sessions of interactive PC training in clinical settings combined with four telephone interviews with health advisors over a 24-month period have been shown to have a positive impact on protective behaviour, with decision balance acting as a mediator variable [453]. Multimedia interactive training or intervention programs have also been implemented in other health-related settings such as a pharmacy with moderate results [456].

Multiple communications achieve better effects in changing risk behaviours than handing out a standard brochure once [450]; [455].

Multimedia interactive training materials could also be used effectively in a setting-specific manner in primary prevention with third and fourth grade children. Hornung et al. [454] were able to show that the provision of information through a CD-ROM compared to teacher-led didactic interventions with brochures can have a positive effect on knowledge and attitude levels [454]. Evidence of the superiority of multimedia forms of delivery (video) over conventional routes via brochures can also be found in Idriss et al. and Janda et al. [461]; [463].

However, on the basis of existing studies, the positive effect of such prevention programmes can only be assumed for complex training programmes that integrate various textual, visual, and audiovisual elements. In many studies [453]; [459]; [456]; [458], the programmes were not tested against the effect of other programme profiles (other delivery channels or other forms or combinations of information presentation and processing), so that on this basis, despite the high level of evidence in some of the studies, it is not possible to draw any conclusions about exactly which measures or which components of a training programme have an effect and which do not contribute to an improvement in knowledge, attitude, and behavioural parameters. In studies in which different forms and ways of presenting information are compared with each other, e.g. [454]; [461]; [463]; [456], other biasing factors may have been at work, which are also reflected in the lower level of evidence. In addition, these studies only provide evidence of the effect of a complex and multi-part bundle of measures, so that no statement can be made about the potential preventive influence of individual components.

Design of Messages

From various studies on prevention campaigns on sun protection behaviour, indications can be derived on the selection of effective message strategies. The effect of different message designs on behaviour change has not been clearly proven. For this reason, no recommendation is made.

Gallagher et al. 2012 examined messages in relation to framing, i.e., the different formulations of a message with the same content. They were able to show in a meta-analysis on the effects of gain and loss framing that gain-framed messages are more effective in promoting preventive behaviours, particularly regarding skin cancer. In contrast, in the 2016 study by Mays et al. loss-framed messages were more successful in decreasing tanning intentions or abandoning them altogether among female tanning bed users aged 18-30. Therefore, the framing statements are too contradictory to derive a general statement.

Dillard and Hissler (2015) were able to show that the type of message (statistical/narrative) and the type of information processing (experiential/rational) influence risk perception and concern. Participants' risk perception and concern were higher when they processed the narrative message experientially. No influence on behavioural intentions was demonstrated. Similarly, the results of Janssen et al. 2013 showed that narrative formats led to higher risk perceptions among tanning salon users. In another study by Lemal et al. 2010, individuals who read the message with narrative were two to four times more likely to take health-promoting actions than individuals in the control group.

Myrick et al. (2015) examined the extent to which different emotional YouTube videos with prevention appeals influence willingness to change behaviour in an experiment with individuals from the United States between the ages of 18 and 69. They were able to show that videos with mixed emotions (fear and humor) were best at generating empathy, which in turn increased willingness to share the information and change behaviour.

Ruppert, 2017 and Strekalova, 2017 are both analyses of the content of YouTube videos and Facebook posts, respectively. From these studies, it can be deduced that the quality of corresponding videos is poor, as they contain false or misleading information about tanning beds or sunscreen. The analysis of Facebook posts showed that images and links were the most shared content. Posts with a risk reference were shared, commented on, and liked more often than those without a risk reference.

 
Personalized and tailored messages

The systematic review by Finch et al. [468] showed numerous promising effects of short personalized messages delivered by SMS, email, or via an app. However, in the studies considered, the influence on sun protection behaviour was mostly measured using only subjective variables. The authors complain that objective factors such as the incidence of sunburn were too rarely examined.

Glanz et al. [465]; [466]

showed in their studies an effect of personalized information (addressing families with children at moderate or increased risk of skin cancer) on some sun protection behaviours such as wearing clothes, hats, sunglasses, using sunscreen, and staying in the shade.

A web-based interactive and individualized intervention significantly improved self-reported sun protection behaviours over control groups in the Heckman et al. [467] study.

Crane et al. [464] examined the effect of a personalized newsletter sent to parents over three years that included sun protection information. There was a small increase in sun protection behaviours compared to a control group. The authors conclude that the intervention alone is not sufficient to reduce skin cancer risk but is promising as one component in a multi-component intervention.

Health information that is tailored to personal characteristics, behaviour patterns, needs, and beliefs is more likely to be perceived as personally relevant and therefore has a stronger motivating character than information that contains general information and advice. This so-called tailoring should take the form of, for example, personalized feedback on risk status, tailored behavioural recommendations, and reminders.

Prevention and intervention programmes that address individuals via personal contact with a health professional or in the form of direct media have stronger evidence of their effect on the perception of cancer risk than do interventions that start at the collective level, i.e., do not specifically address individuals [469]. 

he systematic review of studies also provides evidence that individualised targeting or information tailored to individual risk status ("tailoring") is more effective than general information.

Evidence for the effectiveness of "tailoring" is also provided by Glanz et al. [450]. For adults at moderate to high risk of skin cancer, the authors were able to demonstrate a positive effect with individual protective measures/self-checks as well as a change in the mean value of sun protection behaviour in the context of an information package delivered by post three times at two-week intervals compared to a non-personalised intervention in the form of general educational material on skin cancer prevention and self-examination as well as a brochure on sun protection measures and behavioural tips. Feedback was personalized based on individual risk status and personal risk factors, as well as on practiced sun protection behaviours, behaviour change readiness, and perceived barriers to behaviour change. The constructs "risk perception," "cost and benefit trade-offs of behaviour change," "action-relevant knowledge and skills," and "social norms" were included as mediating variables [450].

Adams et al. [453] were also able to demonstrate positive influences on sun protection behaviour for adolescents using an interactive PC training programme with personalised feedback and telephone interviews with health advisors. Personalised feedback with tips on different types of sun protection behaviour and a bottle of sunscreen were sent by post following the interviews [453].

Similarly, Glazebrook et al. [459] worked with individualised feedback on risk status as part of their interactive PC training for at-risk individuals, which was a fear appeal aimed at increasing perceived threat and, in terms of practising protective behaviour, simultaneously provided information to lower barriers and increase perceived benefits. It contributed to an increase in knowledge, particularly among individuals with higher risk status [459]. Again, however, the programme was not tested against non-personalised training, so evidence on the effect of individualised information and feedback elements remains limited despite a high level of evidence from the studies in this regard.

Involvement of Peers and Multipliers

Peers
Incorporating peer communication into measures of information about primary and secondary skin cancer prevention is promising, as research shows that peer communication has a moderating effect on the relationship between descriptive norms (what the majority would do or consider appropriate) and behaviour. This can be illustrated by the example of alcohol consumption among students. Alcohol consumption is influenced by more than descriptive norms. Peer communication also has a crucial influence here [470]. Therefore, peer communication is likely to support behavioural change.

Socialization Agents

Socialization, as one of the most important processes of internalization, also provides the opportunity for information. Within the socialization process, for example, parents, educators, teachers, etc. take the role of socialization agents [471]. By training and informing socialisation agents, they can act as well-informed multipliers.

In addition, the communication and role model behaviour of parents is also considered to be an important factor influencing the sun protection behaviour of young people [472].

Other Multipliers

Physicians and other medical actors such as pharmacists are considered important multipliers for the primary prevention of skin cancer. The medical setting is therefore discussed in more detail in section 5.4.2.3.

Use of New Media

Many interventions use new media as communication strategies. Finch et al. [468] 

refer in their systematic review to five interventions (investigated in the form of RCTs) that positively change sun protection behaviour with the help of regular short messages (SMS) to the mobile phone. However, in most cases, the control group did not receive any intervention, so that conclusions about the effect of the communicative strategy are not possible.

The effects of interventions that use websites as a communication medium and aim to promote sun protection behaviour [467] or reduce the use of sunbeds [473], among other things, with the help of modularly structured and partly individually tailored topic blocks, showed positive effects on behaviour. But again, no conclusions can be drawn about the actual effect of the web-based approach compared to other approaches.

Falzone [474] 

derive important factors for the design of social media campaigns from their review on psychosocial factors influencing tanning behaviour in sunbeds among adolescents and young adults. Thus, in addition to individual factors (such as internalized tanning norms, body satisfaction, and comorbidities with other mental illnesses such as eating disorders), they also name family (e.g. communication with parents and role models), peers (such as their body ideals and tanning salon use), and factors at the societal level (such as legislation, advertising, and cultural beauty ideals). Through social media, they believe that greater reach can be achieved in this age group at a lower financial cost, which can influence norms and ideals about beauty and appearance. In addition, they hope this will increase support for government action to ban tanning salon use by young people.

In terms of targeting children, adolescents, and young adults, there is evidence in the literature about which media are appropriate for reaching this audience. For example, Adams et al. found that children and adolescents aged 10 to 16 years who participated in education via computer had lower risk behaviours regarding their sun exposure than individuals in the control group [453]. 

This effect is presumably due to a change in decision balance (subtracting the benefits of sun exposure from those of sun protection) as a result of the intervention.

Hornung et al. report on an intervention which was directed at third and fourth grade students. The content of the intervention was knowledge about the dangers of UV radiation, attitudes toward sun tanning, and behavioural practices to protect against UV radiation. Different communication channels were used. First, one group received the content via CD-ROM (IG 1), others received teacher-led didactic instruction (IG 2), and a third group received no intervention (CG). In both groups, teachers received general information and information on the implementation of each intervention. The results show that in IG 1 knowledge increased the most, attitudes improved the most, and possible behaviours were demonstrated more often compared to IG 2 and CG. After seven months, the effects within IG 1 weaken and can no longer be statistically significantly distinguished from IG 2, but there are significant differences between these two groups and the CG in knowledge about the dangers of UV radiation. In terms of attitude, only IG 1 and CG are still significantly different from each other, while in terms of behaviour, no differences between the groups exist anymore [454].

Idriss et al. [461] provide evidence that among internet-savvy young adults (18 to 39 years), web-based communication media (online videos) are superior to purely text-based media (print media) in their effectiveness in conveying knowledge about malignant melanoma (p<0.05). Effectiveness was inferred based on changes in participants' melanoma knowledge at baseline compared to one month after receiving the educational intervention (questionnaire survey).

Outward Appearance Targeting

As appearance is a major motive for sun tanning/tanned skin, especially for women [475], appropriate messages/appeals can address this motive and highlight possible loss of attractiveness due to unhealthy behaviour. Thus, consequences such as skin ageing and spots on the face (due to excessive skin tanning) are used in prevention campaigns (Dodd / Forshaw 2010).

Particularly for studies on women, these appeals showed high effectiveness in preventing skin cancer. Appeals arguing for loss of attractiveness showed positive (i.e. socially desirable) effects on risk perception, self-efficacy, attitudes, behavioural intentions, and behaviour. This is illustrated not only by the many individual studies (for a review, see [476]) conducted by Mahler and colleagues in particular, but also by two research reviews on appearance-based interventions for sun protection [477]. However, the studies on attractiveness appeals were often conducted exclusively (or at least a majority) with women (Williams et al. 2013). Williams (2013) randomised a total of 70 female students from Staffordshire University in the UK to one of two intervention groups. The first intervention group used the facial ageing programme "Age Progression Software" (APRIL). An image with UV protection and an image without were then placed side by side and the women were asked about their thoughts on the two. The second intervention group received information leaflets from the National Health Service and Cancer Research UK and were then also interviewed. Each intervention group was considered a respective control for the other. Endpoints represented attitudes towards benefits and risks of sun exposure, future sun protection intention, and perceived sun damage susceptibility.

 personalized variant for visualizing the possible loss of attractiveness are interventions such as UV photography or "facial morphing" (e.g. "ageing software").

Here, however, the mostly insufficient clarification of the health relevance of the visualizations, which are used as a means to influence behaviour, is viewed critically. For this reason, although positive indications of at least short-term behavioural changes have emerged from studies, no recommendation is made in the context of this guideline.

An appearance-based web-based intervention by Hillhouse et al. [473] was able to reduce intention to use tanning beds in female adolescents. The change of psychosocial variables (attitudes, perceptions, expectations, and norms) is of particular importance.

In the randomized controlled trial by Blashill et al. [481], the use of skin ageing software reduced the frequency of outdoor and tanning bed tanning in young adults compared to the use of information brochures alone or brochures combined with mindfulness exercises. This effect diminished over time. Similarly, Williams et al. [477] reported benefits of a computerized facial aging simulation intervention in young women in positively influencing intentions and attitudes toward UV exposure compared with the use of informational brochures alone.

A UV photo designed to visualize the contrast between UV-damaged and healthy skin was used in the Heckman et al. [480] study and was found to be significantly more effective in positively influencing behaviour change toward sun protection than standardized skin cancer prevention information brochures. Participants were 82% female.

Hollands et al. [482] find little evidence that the use of images visualizing individual "UV damage" or signs of skin ageing contributes to behaviour change [482]. Other research suggests that, for example, cues supported by UV photographs of negative consequences of excessive UV radiation on appearance can positively influence sun protection behaviour, at least in some target groups [483], [484]; [485]; [486].

Self-Examinations

There are no systematic studies on the question of whether and to what extent risk assessment or sun protection behaviour is influenced by regular self-examination of the skin. This is seen as a deficit. Robinson et al. (2007) point out that in the randomized controlled trial they conducted in a high-risk group, concern about UV-induced skin damage decreased in an intervention group. In this intervention group, self-examination was performed with a partner (definition of high-risk group: melanoma patients, individuals with melanoma patients within the family, or individuals with > 50 nevi or > 2 atypical nevi). As an explanation, the authors suggest that perhaps confidence in one's own ability to control the skin had increased [487]. Whether and in what way the sun protection behaviour of the subjects was actually influenced by the intervention was not investigated.

Need for Research

When evaluating screenings and/or studies on self-examination of the skin, the effects on risk perception and sun protection behaviour should also be surveyed.

As already described in detail in section 5.2 , sun protection and exposure behaviour as well as knowledge about skin cancer and risk factors differ in different population groups. Identified distinguishing criteria and target groups are gender [404], age (e.g. children and adolescents) [411], skin cancer sufferers and relatives [408], and organ donation recipients [416]. Following the public health action cycle, a precise problem identification including the target group-specific needs and requirements is necessary for the successful implementation of measures [488].

In addition, different access routes are suitable for reaching these different target groups. The setting approach was first mentioned in the Ottawa Charter of the WHO [489] and is considered a core strategy of health promotion and describes the need to reach people in their direct living environment and to change it (see relationship prevention) in order to bring about an improvement in health.

In the following, some selected target groups are focused on and knowledge about existing access routes and special features is listed. (Note: occupation-specific aspects and, in particular, the target group of outdoor workers are listed specifically in Chapter 7).
 
Children and Adolescents

Most of the available interventions were directed at the target group of children either directly or indirectly through parents, teachers, educators, or other caregivers. This makes sense for several reasons. On the one hand, childhood and adolescence represent an essential phase of life for the later risk of skin cancer, and on the other hand, several studies prove the potential for at least short- and medium-term positive influence on sun protection behaviour in 9-year-old primary school children [438], five- to six-year-old primary school children ("Kidskin," [492]; [493]), and preschool children [437]. In intervention groups, compared to control groups, use of textile sunscreen [438]; [437]; [492]; [493], use of sunscreen [437], avoidance of being outdoors during the sunniest time of day [438], or seeking shade [437]; [492]; [493] increased. In addition, the pathway "protecting children" could also influence the behaviour of the adults caring for them [437].

Already in four- to five-year-old children, an age-appropriate intervention using, for example, games, songs, and picture books improved knowledge about sun protection compared with a control group. The effect was still significant in the intervention groups of a randomized controlled trial (sample of 12 classes with preschool children aged four to five years) seven weeks after the end of the intervention. However, adult help is needed in this age group to translate knowledge into practical action. For this reason, the authors emphasize the need to involve parents in the intervention [388].

Few studies examined effects on endpoints such as skin tanning or number of nevi. That appropriate school-based campaigns have the potential to influence these endpoints as well, at least to a moderate extent, was demonstrated by the intervention study "Kidskin," conducted over five years on five- to six-year-old elementary school children. After two years, reduced sun exposure and less tanning were described in the intervention groups compared with the control group. After five years, a slightly (although not statistically significant) lower number of nevi was observed in the intervention groups compared to the control group [491]; [493].

In contrast, the SoleSi SoleNo-GISED [494] 

intervention program implemented in Italian primary schools showed no effect on the endpoint "number of sunburns" or the number of nevi one year after the intervention. As possible explanations for the negative result, the authors discuss the already high level of sun protection in the study population before the intervention, the rather general information material, and the too-short follow-up of only one year with regard to the number of nevi.

No evidence of adverse effects of interventions in schools to improve appropriate sun protection behaviour emerged from the available studies. In particular, there was no difference between children from sunscreen intervention groups and control groups in terms of body mass index or self-reported outdoor activity [362].

 
Users of Sunbeds

As detailed in Section 5.1.1.5, the use of sunbeds correlates directly with the development of skin cancer and should therefore be avoided. As the data from the NCAM study show (see Section 5.2.2), use is age-specific, with particular emphasis on the fact that young people still use tanning salons despite §4 of the NiSG. Increased use by people from migrant backgrounds and with intermediate levels of education was also recorded.

Recipients of Organ Donations and Skin Cancer Sufferers

Particularly in the case of adolescents and adults, the importance of a personal approach (e.g. in the context of a doctor-patient consultation) has been shown to be effective in influencing behaviour. Evidence from several studies shows that individualized interventions (individual risk assessment, personal doctor-patient consultation) increase the chances of influencing behaviour. A physician consultation with individually tailored feedback reports showed significant differences in sun protection behaviour between intervention group and control group in 11- to 15-year-olds even 24 months after the intervention [390]. Falk and Magnusson [496] sshowed that face-to-face advice on sun protection behaviour during a medical consultation, combined with an examination of existing nevi, still led to improved sun protection behaviour in adults three years after the intervention but significantly improved only with regard to sunscreen use. Information by letter alone had no effect. An appearance-focused intervention strategy tailored to the target group of sunbed users showed effects on attitude and behaviour (number of sunbed visits) in young female sunbed users [483], [484].

Rat et al. [495] investigated a dichotomous risk assessment in the doctor's office and were able to show that sun exposure could be reduced through targeted counselling of high-risk patients.

Need for Research

There is a need for research on the extent to which it is useful to involve other professional groups in primary prevention and secondary prevention measures. In a randomized study of 54 pharmacists, it was shown that training of pharmacy staff increased counselling activities for primary prevention of skin cancer [497]. However, further research is needed to demonstrate the effectiveness and sustainability of such activities and to derive recommendations.

In Germany, the NiSG, which has been in force since July 2009, and the UVSV, which has been in force since January 2012, represent important measures of protection against artificial UV radiation and thus primary prevention.

According to § 4 NiSG, it is not permitted to allow minors to use sunbeds. Violations are punished as administrative offences. The ban is intended to influence the behaviour of minors with regard to the use of artificial UV radiation for cosmetic purposes by law. However, no studies are available on whether and to what extent attitudes or behaviour of the population in connection with UV protection are changed by this ratio preventive measure.

The UVSV regulates, among other things, requirements for the operation of UV irradiation equipment. All devices (old devices since 1 August 2012) must comply with a maximum sunburn-effective total UV irradiance of 0.3 W/m2 skin for UV-A and UV-B radiation. Since 1 November 2012, qualified specialist staff must be available to fulfil the information obligations under UVSV – regarding, among other things, the effects of UV radiation and the risks associated with sunbed use. There is no study available on whether and to what extent risk assessment and behaviour of the population are influenced by these ratio preventive measures.