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The role of sunscreen preparations in preventing skin cancer

Pauline Buchanan, BSc (Hons), RN, RM, ONC, DipN.

Consultant Nurse, Department of Dermatology, Salisbury District Hospital, Wiltshire; and Honorary Lecturer, Institute of Health Care Studies, University of Bournemouth, Dorset

Skin cancer remains a significant health problem worldwide, despite large-scale preventive programmes (Gallagher et al, 1990; Green, 1984; Lee, 1992). The white adult population is that most at risk of malignant melanoma, basal cell carcinoma and squamous cell carcinoma, all of which are primary cutaneous malignancies caused by excessive sun exposure (Gallagher et al, 1987).

Skin cancer remains a significant health problem worldwide, despite large-scale preventive programmes (Gallagher et al, 1990; Green, 1984; Lee, 1992). The white adult population is that most at risk of malignant melanoma, basal cell carcinoma and squamous cell carcinoma, all of which are primary cutaneous malignancies caused by excessive sun exposure (Gallagher et al, 1987).

The incidence of all skin cancers has risen steadily over the past two decades in the UK. The concern with the increasing incidence relates to high mortality associated with malignant melanoma (Office of National Cancer Statistics, 1991-1998) and the efficacy of current skin-cancer prevention campaigns.

Health education is the cornerstone of all primary and secondary campaigns for skin cancer. It is essential in order to prevent skin cancer from arising in susceptible individuals (Box 1) and to diagnose and treat early malignant melanoma. The main UK health-education campaign on skin cancer prevention was the Health Education Authority's 'Sun Know How' campaign, which ran from 1994 until 2001 (HEA, 1994). A key element to this seven-year campaign was informing people how to avoid sunburn by highlighting strategies for protection against the sun, such as seeking shade, wearing protective clothing - such as hats - using sunglasses and applying sunscreens.

There is little argument that these strategies are important in any skin-cancer prevention campaign. However, a recent survey by the Imperial Cancer Research Fund (ICRF, 2001) reported that people still have a desire to tan, and are thus putting themselves at risk of sunburn and skin cancer.

The controversy regarding the use of sunscreens has also led to confusion and apprehension for health professionals and the lay population. Conflicting reports about the value of sunscreens can result in under-use as a method to avoid sunburn and skin cancer. The purpose of this paper is to review the evidence surrounding the use of sunscreens in skin-cancer prevention and to identify clear guidelines for health promotion.

Sunscreens and protection against ultra-violet radiation
Sunscreens were developed to reduce the amount of damage to human skin caused by ultra-violet (UV) radiation. UV radiation comprises three wavelengths, UVC (200-280nm), UVB (280-315nm) and UVA (315-400nm). UVC is known as a carcinogen, however, due to its short wavelength is adequately screened out of the atmosphere by the stratospheric ozone layer.

UVB rays penetrate the skin to the level of the dermo-epidermal junction and is responsible for DNA damage in keratinocytes and solar erythema (sunburn). UVA rays penetrate into the dermis and damage collagen proteins and elastin fibres, thus accelerating ageing of the skin (photoageing). Both UVB and UVA contribute to the formation of skin cancers.

UV radiation damages human skin in two significant ways: it causes direct cellular damage in the skin and immunosuppression at local and systemic levels. The direct tissue and cellular damage may result in delayed erythema (sunburn), premature ageing, DNA damage and mutation that ultimately leads to malignant change or skin cancer (Naylor and Farmer, 1997). Evidence exists linking sunburn and the development of all skin cancers (NRPB, 1995; Osterlind, 1991).

UV radiation adversely affects the immune system by suppressing the immune response within the skin to carcinogens. The primary function of sunscreens therefore is to reduce or limit the amount of UV damage to skin, thus preventing the development of malignancy. Research in both animal and human species has demonstrated that sunscreens can reduce UV damage to skin and facilitate tissue repair (Kligman et al, 1980).

Controversy surrounding sunscreens
Sunscreens were developed to reduce the risk of developing skin cancers. Recently there have been controversial reports in the scientific and popular press linking sunscreen use and increased incidence of skin cancer (Setlow et al, 1993). The debate concerns certain ingredients in organic (chemical absorbers) sunscreen formulations that may be potential carcinogens (Knowland et al, 1993).

Animal studies have been criticised on the basis that animal and human skin differ anatomically and biochemically and that penetration of mutagenic substances to the vulnerable basal layer in human skin is highly unlikely due to the thickness and structure of the stratum corneum in human skin (Naylor and Farmer, 1997). To date there remains no reliable evidence to discourage the use of sunscreens - the well-researched benefits of their use in terms of protection against UV radiation far outweigh the potential theoretical dangers (mutagenicity, altered vitamin-D synthesis and hypersensitivity to the sunscreen formulation).

Published research reports that increased incidence of malignant melanoma is associated with sunscreen use (Garland et al, 1993; Autier et al, 1998). However, a major criticism of this research is that its methods are flawed and do not provide sufficient evidence to support the hypothesis that sunscreens increase the risk of skin cancer (Rigel et al, 2000). For example, one explanation for the observation that melanoma was more common in sunscreen users is that sunscreen users failed to apply sufficient sunscreen to provide protection.

Overwhelming evidence exists linking exposure to the sun with increasing incidence of skin cancer (Gallagher et al, 1987; Gallagher et al, 1990; Green, 1984; Lee, 1992; NRPB, 1995; Osterlind, 1991). As a consequence, epidemiological studies have reported an increased use of sunscreens.

It is important, however, to interpret these findings correctly. The sunscreen-melanoma link is not a cause-and-effect phenomenon. The increased incidence of skin cancer is related to prolonged sun exposure. It is postulated that some sunscreen users deliberately extend exposure time, thus increasing the risk of skin cancer. It is important to consider this in health promotion and discourage patients and clients using sunscreen to remain in the sun for longer periods.

Sunscreen availability and sun protection factors
Sunscreens can be categorised into two main groups, absorbers and reflectors. Absorber sunscreens use a chemical reaction to absorb UVB rays, thus preventing their penetration to the basal layer of the epidermis. Substances typically regarded as absorbers are oxybenzone and ethyhexyl p-methoxycinnamate. These substances are not as effective in screening out UVA rays, which also contribute to the development of skin cancer and premature ageing of the skin.

Reflector sunscreens are physical barriers that reflect or scatter the rays away from the skin. The main ingredient in reflector-type sunscreens is titanium dioxide, for example Sunsense. These sunscreens are very effective at protecting the skin from both UVA and UVB rays. Most absorber and reflector sunscreens are available over the counter at supermarkets, pharmacies and chemists and are categorised as toiletries. However, sunscreens are classified as borderline substances if the preparations are marked 'ACBS' and are regarded as drugs when prescribed for skin protection (BMA/RPSGB, 2000). Many sunscreens are broad spectrum and screen out both UVA and UVB rays, for example Coppertone, Delph, E45 Sun, RoC Total Sunblock, Spectraban and Uvistat.

Sunblock is classified as a sunscreen that protects 100% against UVA. Very few products are 100% protective and all contain a physical barrier (titanium dioxide). In the UK, sunscreens are available for two main purposes. First, as a product that is specifically designed to act as a sunscreen or block. These products are intended for use on holiday, on the beach or during hot sunny weather. The other use of sunscreens is as a secondary component within cosmetics, moisturisers and lipsticks. The sun protection factor (SPF) is important here because the SPF is usually lower if the sunscreen is an addition to a cosmetic product rather than a product in its own right.

Most sunscreens have a SPF between SPF2 and SPF100. The SPF is calculated by each manufacturer for its own particular product and many different standards are used in the determination of SPFs, so it is important to remember that sunscreens from different manufacturers that state the same SPF are likely to offer varying protection.

All SPFs are based on how long it takes for unprotected skin to burn (the average length of time is 10 minutes). The higher the SPF, the greater the protection provided by the sunscreen in length of time. For example, if you use a sunscreen with SPF15, the protection offered would last approximately two-and-a-half hours (10 minutes x 15 = 150 minutes). However, the SPF is an estimate only, therefore care and attention should be given to skin type, the intensity of the rays or sunshine, time of day, season and latitude from the equator.

Nursing assessment
Nurses in primary care will be involved in future skin-cancer prevention programmes. Providing the health education necessary to enhance patient concordance requires accurate assessment of clinical history and patient/client needs (Box 2). Nursing intervention will include providing information on sunscreens that needs to be tailored to the individual.

Conclusion
UV damage and skin cancer is a risk for all fair skinned people. Whether at home, school, college, at leisure or on holiday. Burning should always be avoided. It is the repeated, high intensity UVB exposure that causes burning that is linked with malignant melanoma. Low-intensity chronic exposure to UVA is linked to premature ageing and non-melanoma skin cancers. Some dermatologists claim that any solar-induced tan is a sign of skin damage.

Sunscreens are an important adjunct to the other recommended strategies for protection against the sun, such as clothing, shade, hats and sunglasses. Clear evidence supports the value of sunscreen use in the prevention of UV-induced skin damage and skin cancers. In light of this, the recommendations on sunscreen use are as follows:

- Use sunscreens whenever exposed to strong sunlight, both in the UK (during all outdoor pursuits) and abroad

- Always reapply sunscreens after watersports, games and exercise. Hypoallergenic, water-resistant formulations are available

- Apply a high-SPF sunscreen to children each morning before school during hot spells. Babies under 12 months of age should be kept out of strong sunshine altogether

- Sunscreens should be used according to skin type. The fairer the skin, the greater the SPF needed for protection

- Sunscreens are best viewed as part of a total sun protection plan.

Useful contacts
Wessex Cancer Trust Skin Cancer Information Network: Bellis House, 11 Westwood Road, Southampton S017 1DL. Tel: 02380-672200 Website: www.wessexcancer.org

- Wessex Cancer Trust MACRC'S Line (Melanoma and Related Cancers of the Skin Telephone Information and Support). Tel: 01722-415071

Autier, P., Dore, J.F., Cattaruzza, M.S. et al. For the European Organisation for Research and Treatment of Cancer Melanoma Co-operative Group. (1998)Sunscreen use, wearing clothes, and number of nevi in 6-7-year-old European children. Journal of the National Cancer Institute 90: 1873-1880.

British Medical Association/Royal Pharmaceutical Society of Great Britain. (September 2000)Sunscreen preparations. British National Formulary. London: BMA/RPSGB.

Cancer Research Campaign. (2002)Facts about Malignant Melanoma. Available at: www.crc.org.uk

Gallagher, R.P., Elwood, J.M., Threlfall, W.J. et al. (1987)Socioeconomic status, sunlight exposure and risk of malignant melanoma: the Western Canada melanoma study. Journal of the National Cancer Institute 79: 647-652.

Gallagher, R.P., Ma, B., McLean, D.I. et al. (1990)Trends in basal cell carcinoma, squamous cell carcinoma and melanoma of the skin from 1973 through 1987. Journal of the American Academy of Dermatology 23: 413-421.

Garland, C.F., Garland, F.C., Gorham, E.D. (1993)Rising trends in melanoma: an hypothesis concerning sunscreen effectiveness. Annals of Epidemiology 3: 103-110.

Green, A. (1984)Sun exposure and risk of melanoma. Australian Journal of Dermatology 25: 99-102.

Health Education Authority. (1994)Sun Know How Campaign. London: HEA.

Imperial Cancer Research Fund. (2001)Sun Sense or Sun Abuse? Survey on attitudes to suntans. London: IRCF.

Kligman, L.H., Akin, F.J., Kligman, A.M. (1980)Sunscreens prevent ultraviolet carcinogenesis. Journal of the American Academy of Dermatology 3: 30-35.

Knowland, J., McKenzie, E.A., McHugh, P.J. et al. (1993)Sunlight-induced mutagenicity of a common sunscreen ingredient. Federal European Biochemical Society 324: 309-313.

Lee, J.A.H. (1992)Etiology, risk factors, epidemiology and public health issues in melanoma and other cutaneous neoplasms. Current Opinions in Oncology 4: 347-350.

Naylor, M.F., Farmer, K.C. (1997)The case for sunscreens. Archives of Dermatology 133: 1146-1154.

National Radiological Protection Board. (1995)Health Effects From Ultraviolet Radiation: Report of an advisory group on non-ionising radiation. Oxon: NRPB.

Office of National Cancer Statistics. (2000)Cancer survival in England and Wales, 1991. Health Statistics Quarterly 6: 71-80.

Osterlind, A. (1991)Etiology and epidemiology of melanoma and skin neoplasms. Current Opinions in Oncology 4: 77-82.

Setlow, R.B., Grist, E., Thompson, K. et al. (1993)Wavelengths effective in induction of malignant melanoma. Proceedings of the National Academy of Science, USA 90: 6666-6670.

Rigel, D.S., Naylor, M., Robinson, J. (2000)What is the evidence for a sunscreen and melanoma controversy? Archives of Dermatology 136: 1447-1449.

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