Primary prevention of skin cancerBMJ 1994; 309 doi: https://doi.org/10.1136/bmj.309.6950.285 (Published 30 July 1994) Cite this as: BMJ 1994;309:285
- R Marks
Concern about the effect of stratospheric ozone depletion has drawn attention to the incidence of skin cancer, which is already high in some countries and is increasing in others. Predictions of increased rates of skin cancer associated with ozone depletion are based on the belief that these tumours are related to sunlight.
Many governments and other public health bodies are either contemplating or initiating educational programmes to prevent skin cancer. In Britain the Health of the Nation set the ambitious target “to halt the year-on-year increase in skin cancer by the year 2005.”1 Responding to this, a British working party on skin cancer prevention, comprising representatives of the health professions, health education workers, and cancer funding agencies, has issued a consensus statement on sunlight and skin cancer.2
It lays out in eight points the working party's view that skin cancer is related to overexposure to sunlight and that “in four out of five cases, skin cancer is a preventable disease.” A four point approach to minimising skin damage from the sun is advised: avoid the noonday sun, seek natural shade, wear clothing and hats, and use a broad spectrum sunscreen with a sun protection factor of 15 or above. It is fair to ask what is the basis for those views and what effect, if any, the recommendations will have on the future incidence of skin cancer.
Sunlight was initially suggested as a cause of nonmelanoma skin cancer in the nineteenth century. It was not until the 1950s that it was thought of as a possible cause of melanoma. Since then good quality epidemiological data have indicated that sunlight is important in the development of all of these tumours in those people who are constitutionally predisposed - that is, fair skinned people.3,4
The exact nature of exposure to sunlight needed to cause these tumours has not yet been clearly delineated. Some differences seem to exist between the type of exposures associated with an increased risk of melanoma and an increased risk of non-melanoma skin cancers.3,4 Epidemiological data also suggest that exposure to sunlight in childhood is important in the development of both melanoma and non- melanoma skin cancers. Migration studies show a protective effect for people who do not migrate to areas of high incidence until after childhood and adolescence.5,6
Exposures sufficient to cause sunburn have been associated with increased risks of skin cancer, although not always as high as many people expect.7 The risk of sunburn correlates with the desire for a suntan, although, as the consensus statement states, there may not always be a history of deliberate sunbathing in those people who develop skin cancer.8 High rates of non-melanoma skin cancer occur in outdoor workers whose sunlight exposure is not necessarily related to sunbathing. People engaged in watersports have a high risk of sunburn, again not necessarily related to sunbathing.8
A suntan does not seem to protect adequately against skin cancer. The rate of non-melanoma skin cancer in Australia in people who say they always tan and never burn when exposed to sunlight is around 400/100 000 people per year.9 The effect of the ability to tan on risk of melanoma seems to be slightly more complex. Whether a tan is a sign of already damaged skin is debatable.
Overall, the proportion of skin cancer attributable to sunlight is difficult to estimate. On the basis of published estimates it could be up to 80% or more of the tumours occurring in Britain.10
Although ultraviolet B (ultraviolet radiation of 290-320 nm) is believed to be the main carcinogen in sunlight, there are suggestions that the broad spectrum component ultraviolet A (320-400 nm) may also contribute to some extent. Hence the recommendation to include broad spectrum cover in sunscreens.11
Certainly people would be exposed to substantially less ultraviolet radiation if they could be induced to follow the recommendations in the consensus statement. To date, no one has been able to show that similar recommendations in population based educational programmes reduce skin cancer. One would not expect this outcome in the short term - it could be 20-30 years before a turnaround can be achieved. The target set in the Health of the Nation is probably unrealistic.
Australian data show that changing people's attitudes to suntans and sun protection is possible and can lead to less sunburn.12 Anecdotal studies have suggested a reduced frequency and severity of skin tumours when a sunlight reduction programme has been studiously followed by people with xeroderma pigmentosum. More recently, prevention of new solar keratoses and an increased a randomised controlled trial of regular sunscreen use versus placebo in humans.13
On balance, given our current knowledge and the concern about the added effects of ozone depletion, the recommendations in the consensus statement seem a reasonable position to take. They should be promoted in a way that suggests that people can still enjoy outdoor activities while reducing their sunlight exposure. The recommendations will do little harm at the least and should have the potential to reduce the incidence of what is now becoming a public health problem in many countries throughout the world.