Sun and UV facts and evidence

There is sufficient evidence to show that overexposure to ultraviolet (UV) radiation is the main preventable cause of skin cancers – both melanoma skin cancer (the most serious type) and non- melanoma skin cancers (NMSC).[1,2] The sun is the principal source of natural UV radiation. Sunbeds produce artificial UV radiation.

An estimated 86% of melanoma skin cancers in the UK (around 13,600 cases) every year are linked to too much exposure to sunlight and sunbed use.[2]

The risk of melanoma is most strongly linked to intermittent sun exposure [3] – short, intense bursts of sun for people who generally spend most of their time indoors, for example sunbathers on holiday.

References
1.  International Agency for Research on Cancer. Radiation. Vol 100.; 2012.
2.  Brown, K. et al. The fraction of cancer attributable to modifiable risk factors in England, Wales, Scotland, Northern Ireland and the United Kingdom overall in 2015. British Journal of Cancer 2018 https://www.nature.com/articles/s41416-018-0029-6
3.  Gandini S, Sera F, Cattaruzza MS, et al. Meta-analysis of risk factors for cutaneous melanoma: II. Sun exposure. Eur J Cancer. 2005;41(1):45-60. doi:10.1016/j.ejca.2004.10.016.

Some people are more likely than others to develop skin cancer.

These people tend to have one or more of the following:
o fair skin[1]
o skin that burns easily[1]
o lots of moles[2] or freckles[1]
o a history of sunburn[3]
o red or fair hair[1]
o light-coloured eyes[1]
o a personal[4,5] or family history of skin cancer.[1,6]

People with naturally dark brown/black skin burn less easily and have a lower risk of skin cancer.[1] But people with darker skin can still develop skin cancers, especially types not related to UV for example on non-pigmented parts of the body like the soles of the feet.[7]

References
1.  Gandini S, Sera F, Cattaruzza MS, et al. Meta-analysis of risk factors for cutaneous melanoma: III. Family history, actinic damage and phenotypic factors. Eur J Cancer. 2005;41(14):2040-2059. doi:10.1016/j.ejca.2005.03.034.
2.  Gandini S, Sera F, Cattaruzza MS, et al. Meta-analysis of risk factors for cutaneous melanoma: I. Common and atypical naevi. Eur J Cancer. 2005;41(1):28-44. doi:10.1016/j.ejca.2004.10.015.
3.  Olsen CM, Zens MS, Green AC, et al. Biologic markers of sun exposure and melanoma risk in women: pooled case-control analysis. Int J Cancer. 2011;129(3):713-723. doi:10.1002/ijc.25691.
4.  Balamurugan A, Rees JR, Kosary C, Rim SH, Li J, Stewart SL. Subsequent primary cancers among men and women with in situ and invasive melanoma of the skin. J Am Acad Dermatol. 2011;65(5 SUPPL. 1):S69.e1-S69.e9. doi:10.1016/j.jaad.2011.04.033.
5.  Bradford PT, Freedman DM, Goldstein AM, Tucker M a. Increased risk of second primary cancers after a diagnosis of melanoma. Arch Dermatol. 2010;146(3):265-272. doi:10.1001/archdermatol.2010.2.
6.  Olsen CM, Carroll HJ, Whiteman DC. Familial melanoma: A meta-analysis and estimates of attributable fraction. Cancer Epidemiol Biomarkers Prev. 2010;19(1):65-73. doi:10.1158/1055-9965.EPI-09-0928.
7.  Wang Y, Zhao Y, Ma S. Racial differences in six major subtypes of melanoma: descriptive epidemiology. BMC Cancer. 2016;16(1):691. doi:10.1186/s12885-016-2747-6.

The World Health Organisation (WHO) developed an international UV index to reflect the strength of the sun’s rays (level of UV radiation) at the earth’s surface. There’s a guide to the UV Index available online at: http://www.who.int/uv/publications/en/UVIGuide.pdf . The greater the UV index value, the greater the potential for damage and the less time it takes for this damage to occur.[1,2]

The UV index can be used as an indication for how important it is to protect against UV radiation. It is widely accepted that people are unlikely to be harmed by UV levels below 3.[1,3]

The strength of UV radiation reaching the earth’s surface is affected by several factors including: [2,4,5]
o Time of day, being strongest at solar noon (around 1pm British Summer Time) when the sun is highest in the sky
o Time of year, being strongest in the summer months
o Latitude, being strongest in locations nearer the equator
o Altitude, being higher at higher altitudes
o Cloud cover – over 90% of UV can pass through light cloud
o Reflection – snow can reflect up to 80% of the UV radiation that hits it, increasing a person’s exposure. About 15% of rays are reflected back from sand, 10% from concrete and up to 30% from water (depending on choppiness)

References
1.  World Health Organisation Intersun. UV Index. http://www.who.int/uv/intersunprogramme/activities/uv_index/en/.
2.  World Health Organisation. GLOBAL SOLAR UV INDEX A Practical Guide.; 2002.
3.  World Health Organisation Intersun. Workshop on Review of the UV Index. http://www.who.int/uv/UVI_workshop_Melbourne2015/en/. Published 2015.
4.  International Agency for Research on Cancer. Radiation. Vol 100.; 2012.
5.  Met Office. UV Index. www.metoffice.gov.uk/uv.

Holloway’s rule is an easy way to know when the sun is strong: the sun’s UV rays are strongest when your shadow is shorter than you. So that’s when you’re more likely to burn.[1]

References
1.  Holloway L. Shadow method for sun protection. Lancet. 1990;335:484.

UV radiation from the sun damages the DNA in our skin cells which can lead to the development of cancer.[1] Sunburn is a sign of DNA damage caused by too much UV.  There are two main types of UV rays that damage skin and cause skin cancer[1]:
• UVA penetrates deep into the skin. It ages the skin, but contributes much less towards sunburn[2].
• UVB is responsible for the majority of sunburns.

A third type of UV ray, UVC, could be the most dangerous of all, but it is completely blocked out by the ozone layer and doesn’t reach the earth's surface.[1]

Getting a sunburn just once every two years can triple the risk of melanoma.[3]

Sunburn during childhood or adolescence can increase the risk of skin cancer later on in life. But sunburn at any age increases the risk of malignant melanoma. [3,4]

References
1.  International Agency for Research on Cancer. Radiation. Vol 100.; 2012.
2.  Amano S. Characterization and mechanisms of photoageing-related changes in skin. Damages of basement membrane and dermal structures. Exp Dermatol. 2016;25(May):14-19. doi:10.1111/exd.13085.
3.  Dennis LK, VanBeek MJ, Freeman LEB, Smith BJ, Dawson D V., Coughlin JA. Sunburns and risk of cutaneous melanoma, does age matter: a comprehensive meta-analysis. Ann Epidemiol. 2008;18(8):614-627. doi:10.1016/j.annepidem.2008.04.006.Sunburns.
4.  Gandini S, Sera F, Cattaruzza MS, et al. Meta-analysis of risk factors for cutaneous melanoma: II. Sun exposure. Eur J Cancer. 2005;41(1):45-60. doi:10.1016/j.ejca.2004.10.016.

It is widely agreed that a combination of measures including using shade and clothing as the first lines of defence and sunscreen for the parts you can’t cover, offers the best protection against over-exposure to UV radiation from the sun.[1,2] Research suggests that shade and clothing offer better protection from UV rays than sunscreen. [3–6]

Shade
Shade structures can provide protection from the sun. Staying under shade, such as a tree or umbrella, can reduce your overall exposure to UV, but not completely protect you.[7]  Many shade structures are more likely to filter than to block UV radiation. Only very broad and thick shade such as thickly wooded areas and widely overhanging structures provide enough protection from strong sun.[8]

Clothes, hats, sunglasses
Covering up with clothes, hats and sunglasses is an effective way of protecting yourself from UV rays.[2]

Clothes tend to provide more protection if they:[1,2,9–12]
o Cover more skin – e.g. long-sleeved t-shirts and wide brim hats
o Are loose fitting
o Are deeper colours
o Are made of polyester preferably, or wool, silk or nylon. Cotton, rayon, linen and viscose fabrics tend to be less protective
o Are dry – for example cotton is less protective when wet
o Are thicker
o Have a close weave– check you can’t see through the fabric.

Wide-brimmed hats provide the most UV protection for the whole face and head.[1,2] Caps protect the nose and forehead but provide poor protection for other parts of the face.

Sunglasses can protect your eyes from too much UV exposure. Poorly-fitting sunglasses offer poor protection as sunlight can reflect off the back face of the lens back into the eye.  Wraparounds are recommended.[2] Because of the angle of the sun, eyes can be at risk of damage and need protection earlier in the morning and later in the afternoon than for the rest of your body.[13]

Sunglasses should state that they block out 100% of UVA and UVB rays. Alternatively, look for the ‘CE Mark’ and British Standard, or a UV 400 label.

Sunscreen
Many studies have shown that sunscreen can reflect or absorb harmful UV rays.[14] However, whether or not using sunscreen reduces skin cancer risk remains unclear.[15–18] How sunscreen is applied and how using it affects someone’s subsequent behaviour, consciously or unconsciously, are important considerations.[19]

Using sunscreen for ‘non-intentional’ sun exposure, where the aim of the activity isn’t to expose skin to the sun but it may happen incidentally, such as walking, gardening, sport or other daily activities, may reduce the risk of sunburn.[20] However, using sunscreen for ‘intentional’ sun exposure (e.g. sunbathing) has been linked with people spending longer in the sun overall and being no less likely, perhaps even more likely to get sunburnt.[21] This was particularly seen when people used higher SPF sunscreens.

Because of this, we recommend that sunscreen should be used together with clothing and shade to protect the skin from sun damage, and should never be used to spend longer in the sun.

The SPF or ‘factor’ of a sunscreen is a measure of the amount of sun protection it provides. Experts have found that SPF 15 sunscreen provides sufficient protection when used appropriately, wherever you are in the world.[14,22] One study has found benefit for reduction in skin cancer risk for sunscreens of SPF15 or above, compared to below SPF 15.[18] A minimum of SPF 15 is recommended by NICE (National Institute for Health and Care Excellence).[2] No sunscreen is 100% effective and as SPF increases, sunscreens provide less and less extra protection.[19]

SPF measurements are based on the assumption that people apply 2mg/cm2 of sunscreen on their body.[14] But research has shown that people don’t apply enough. Studies have found the actual amount applied is less than half of the level SPF is tested at (0.39 to 1.0 m/cm2).[23]

Sunscreen only works if you use enough. It should be applied evenly, thickly and regularly to be effective.[2] As a guide, for an average adult, you should use:[2]
o around two teaspoonfuls of sunscreen if you're just covering your head, arms and neck.
o around two and a half tablespoonfuls if you're covering your entire body, for example while wearing a swimming costume.

Sunscreens that provide UVA protection are recommended.[2] The star rating system measures the balance between UVA and UVB protection and awards products a rating of 1-5 stars. It is not an absolute measure, but depends on the SPF rating of the sunscreen it is applied to. Sunscreen with at least 4 stars is recommended.[2]

References
1.  International Agency for Research on Cancer. How can I protect myself and my children from the sun in everyday life, during outdoor activities, or while on holiday? European Code Against Cancer. http://cancer-code-europe.iarc.fr/index.php/en/ecac-12-ways/sun-uv-expos....
2.  National Institute for Health and Care Excellence. Sunlight exposure exposure : risks and benefits. 2016;(February).
3.  Linos E, Keiser E, Fu T, Colditz G, Chen S, Tang JY. Hat, shade, long sleeves, or sunscreen? Rethinking US sun protection messages based on their relative effectiveness. Cancer Causes Control. 2011;22(7):1067-1071. doi:10.1007/s10552-011-9780-1.
4.  Autier P, Doré JF, Cattaruzza MS, et al. Sunscreen use, wearing clothes, and number of nevi in 6- to 7-year-old European children. European Organization for Research and Treatment of Cancer Melanoma Cooperative Group. J Natl Cancer Inst. 1998;90(24):1873-1880. doi:10.1093/jnci/90.24.1873.
5.  Lazovich D, Vogel RI, Berwick M, Weinstock MA, Warshaw EM, Anderson KE. Melanoma risk in relation to use of sunscreen or other sun protection methods. Cancer Epidemiol Biomarkers Prev. 2011;20(12):2583-2593. doi:10.1158/1055-9965.EPI-11-0705.
6.  Ackermann S, Vuadens A, Levi F, Bulliard J. Sun protective behaviour and sunburn prevalence in primary and secondary schoolchildren in western Switzerland. Swiss Med Wkly. 2016;(November). doi:10.4414/smw.2016.14370.
7.  International Agency for Research on Cancer. Am I safe on a cloudy day or under a parasol? European Code Against Cancer. http://cancer-code-europe.iarc.fr/index.php/en/ecac-12-ways/sun-uv-expos....
8.  Parisi A V, Turnbull DJ. Shade provision for UV minimization: a review. Photochem Photobiol. 2014;90(3):479-490. doi:10.1111/php.12237.
9.  Hatch KL, Osterwalder U. Garments as solar ultraviolet radiation screening materials. Dermatol Clin. 2006;24(1):85-100. doi:10.1016/j.det.2005.09.005.
10.  Davis S, Capjack L, Kerr N, Fedosejevs R. Clothing as protection from ultraviolet radiation: which fabric is most effective? Int J Dermatol. 1997;36(5):374-379.
11.  Gambichler T, Rotterdam S, Altmeyer P, Hoffmann K. Protection against ultraviolet radiation by commercial summer clothing: need for standardised testing and labelling. BMC Dermatol. 2001;1:6. doi:10.1186/1471-5945-1-6.
12.  Almutawa F, Buabbas H. Photoprotection: clothing and glass. Dermatol Clin. 2014;32(3):439-448.
13.  Gies P. Effectiveness of Sunglasses. 2015;(December):1-13. http://www.who.int/uv/04_Gies_Effectiveness_of_Sunglasses.pdf?ua=1.
14.  IARC. IARC Handbook on Cancer Prevention Vol 5 Sunscreens. Lyon, France; 2001.
15.  Diffey BL. Sunscreens as a preventative measure in melanoma: An evidence-based approach or the precautionary principle? Br J Dermatol. 2009;161(SUPPL. 3):25-27. doi:10.1111/j.1365-2133.2009.09445.x.
16.  Green AC, Williams GM, Logan V, Strutton GM. Reduced melanoma after regular sunscreen use: Randomized trial follow-up. J Clin Oncol. 2011;29(3):257-263. doi:10.1200/JCO.2010.28.7078.
17.  Sánchez G, Nova J, Rodriguez-Hernandez AE, et al. Sun protection for preventing basal cell and squamous cell skin cancers. Cochrane Database Syst Rev. 2016;2016(7). doi:10.1002/14651858.CD011161.pub2.
18.  Ghiasvand R, Weiderpass E, Green AC, Lund E, Veierod MB. Sunscreen Use and Subsequent Melanoma Risk: A Population-Based Cohort Study. J Clin Oncol. 2016. doi:10.1200/JCO.2016.67.5934.
19.  IARC. IARC Handbooks of Cancer Prevention Volume 5 Sunscreens. Vol 5.; 2001.
20.  Autier P, Boniol M, Doré JF. Sunscreen use and increased duration of intentional sun exposure: Still a burning issue. Int J Cancer. 2007;121(1):1-5. doi:10.1002/ijc.22745.
21.  Autier P. Sunscreen abuse for intentional sun exposure. Br J Dermatol. 2009;161(SUPPL. 3):40-45. doi:10.1111/j.1365-2133.2009.09448.x.
22.  Diffey B. Has the sun protection factor had its day? BMJ. 2000;320(7228):176-177. doi:10.1136/bmj.320.7228.176.
23.  Petersen B, Wulf HC. Application of sunscreen - theory and reality. Photodermatol Photoimmunol Photomed. 2014;30(2-3):96-101. doi:10.1111/phpp.12099.

The International Agency for Cancer Research (IARC) state there is sufficient evidence that sunbed use causes melanoma, and limited evidence that sunbed use causes squamous cell carcinoma (a type of non-melanoma skin cancer).[1,2]

Combining the results of studies on sunbeds and cancer shows that using a sunbed at any age increases melanoma risk by 16-20%.[3,4]

Sunbeds are no safer than exposure to the sun itself.[1] One study found that the average skin cancer risk from sunbeds can be more than double that of spending the same length of time in the Mediterranean midday summer sun.[5]

References
1.  International Agency for Research on Cancer. Radiation. Vol 100.; 2012.
2.  EU SCHEER Scientific Committee on Health and Environmental Risks. Opinion on Biological effects of ultraviolet radiation relevant to health with particular reference to sunbeds for cosmetic purposes. 2016;(Nov):8. doi:10.2772/ISBN.
3.  Boniol M, Autier P, Boyle P, Gandini S. Cutaneous melanoma attributable to sunbed use: systematic review and meta-analysis. BMJ. 2012;345(jul24_2):e4757. doi:10.1136/bmj.e4757.
4.  Colantonio S, Bracken M, Beecker J. The association of indoor tanning and melanoma in adults: systematic review and meta-analysis. J Am Acad Dermatol. 2014;70(5):847-857.
5.  Tierney P, Ferguson J, Ibbotson S, Dawe R, Eadie E, Moseley H. Nine out of 10 sunbeds in England emit ultraviolet radiation levels that exceed current safety limits. Br J Dermatol. 2013;168(3):602-608. doi:10.1111/bjd.12181.

UV exposure (including sunbeds) causes premature ageing of the skin (photoageing) – by destroying collagen and elastic fibres, and changing the structure and function of the skin layers.[1,2] UV-induced damage in the skin can cause wrinkles, sagging, leathery appearance, fragility and weakened healing ability.[1]

References
1.  Amano S. Characterization and mechanisms of photoageing-related changes in skin. Damages of basement membrane and dermal structures. Exp Dermatol. 2016;25(May):14-19. doi:10.1111/exd.13085.
2.  EU SCHEER Scientific Committee on Health and Environmental Risks. Opinion on Biological effects of ultraviolet radiation relevant to health with particular reference to sunbeds for cosmetic purposes. 2016;(Nov):8. doi:10.2772/ISBN.

Far from being a sign of health, a tan is a reaction to DNA damage in the skin.[1] It is a sign that your body is trying to repair damage that has already happened.[2]

Some people think a pre-holiday tan or sunbed tan will protect them from burning but a tan offers very little protection against the sun.[3] Some studies have found that tans only offer protection equivalent to using SPF 3 sunscreen – nowhere near the minimum recommended SPF15 -  and tans from sunbeds that mostly produce UVA radiation could be as low as SPF 1.[4]

References
1.  International Agency for Research on Cancer. Is there such a thing as a “healthy tan”? http://cancer-code-europe.iarc.fr/index.php/en/ecac-12-ways/sun-uv-expos....
2.  Agar N, Young AR. Melanogenesis: A photoprotective response to DNA damage? Mutat Res - Fundam Mol Mech Mutagen. 2005;571(1-2 SPEC. ISS.):121-132. doi:10.1016/j.mrfmmm.2004.11.016.
3.  Kirk L, Greenfield S. Knowledge and attitudes of UK university students in relation to ultraviolet radiation (UVR) exposure and their sun-related behaviours: a qualitative study. BMJ Open. 2017;7(3):e014388. doi:10.1136/bmjopen-2016-014388.
4.  Coelho SG, Yin L, Smuda C, Mahns A, Kolbe L, Hearing VJ. Photobiological implications of melanin photoprotection after UVB-induced tanning of human skin but not UVA-induced tanning. Pigment Cell Melanoma Res. 2015;28(2):210-216. doi:10.1016/j.immuni.2010.12.017.Two-stage.

“Fake tan” lotions, sprays, creams and mousses are products applied to the skin that contain the active ingredient dihydroxyacetone (DHA). DHA is a chemical which reacts with the protein in the top layer of skin, to form brown-black compounds called melanoidins.[1]

In 2010, experts at the Scientific Committee on Consumer Safety, part of the European Commission, concluded that DHA-containing fake tan products do not pose a health risk to consumers.[1] You can read the report here (https://ec.europa.eu/health/scientific_committees/consumer_safety/docs/s...) and the FDA also have more recent information on their website (https://www.fda.gov/Cosmetics/ProductsIngredients/Products/ucm134064.htm).
Some DHA-containing products also contain sunscreen but will provide very little protection [2] so shade, clothing and sunscreen are still important when the sun is strong.

References
1.  Scientific Committee on Consumer Safety. Opinion on Dihydroxyacetone. Eur Comm. 2010;(December):SCCS/1347/10; pp 1-35. doi:10.2772/27149.
2.  Faurschou A, Wulf H. Durability of the sun protection factor provided by dihydroxyacetone. Photodermatol Photoimmunol Photomed. 2004;20(5):239-242.

Our bodies produce vitamin D when our skin is exposed to UV rays from the sun. This is the main source of this vitamin.[1] We all need vitamin D to help build and maintain strong bones. If you are severely lacking in vitamin D this may lead to rickets in children and a condition called osteomalacia in adults.[1]

In summer, most white people in the UK only need to spend a short amount of time in the sun unprotected to make enough vitamin D.[1–3] This is typically less than the time taken to lead to sunburn.[3] People with darker skin tones might need longer in the sun, but also have a lower risk of sunburn and skin cancer.[3,4] It should be possible for most people to find a balance between enjoying the beneficial effects of the sun while not increasing the risk of skin cancer.

Vitamin D synthesis is much lower in winter months in countries at higher latitudes like the UK because the UV isn’t as strong.[5] In summer some vitamin D may be stored to help maintain levels across the year.[1,2,6]

The Government recommends that people at risk of vitamin D deficiency should take vitamin D supplements throughout the year. Between October and the end of March they also recommend people in the UK consider taking a daily vitamin D supplement. You can find out more here: http://www.nhs.uk/Conditions/vitamins-minerals/Pages/Vitamin-D.aspx

References
1.  Scientific Advisory Commitee on Nutrition. Vitamin D and Health. 2016:116-130. http://dermatology.jwatch.org/cgi/content/full/2009/522/1.
2.  Independent Advisory Group on Non-ionising Radiation. Ultraviolet Radiation, Vitamin D and Health. 2017;(March).
3.  Felton SJ, Cooke MS, Kift R, et al. Concurrent beneficial (vitamin D production) and hazardous (cutaneous DNA damage) impact of repeated low-level summer sunlight exposures. Br J Dermatol. 2016. doi:10.1111/bjd.14863.
4.  Farrar MD, Webb AR, Kift R, et al. Efficacy of a dose range of simulated sunlight exposures in raising vitamin D status in South Asian adults: Implications for targeted guidance on sun exposure. Am J Clin Nutr. 2013;97(6):1210-1216. doi:10.3945/ajcn.112.052639.
5.  National Institute for Health and Care Excellence. Sunlight exposure exposure : risks and benefits. 2016;(February).
6.  Heaney RP, Davies KM, Chen TC, Holick MF, Janet Barger-Lux M. Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. Am J Clin Nutr. 2003;77(1):204-210.