Sunscreens were primarily designed to prevent sunburn.1 Epidemiologic studies have shown that people with a history of sunburn are at greater risk of developing cutaneous melanoma. Because sunscreen use delays the occurrence of sunburn, and also delays the onset of a variety of other ultraviolet-induced skin lesions,2 these product shave been advocated for the prevention of skin cancer. It is generally assumed that the greater the ability of a sunscreen to delay sunburn, denoted by its sun protection factor (SPF), the greater its protection against melanoma.
High SPF suncreen does not protect against sunburn during intentional sun exposure
The laboratory data on the properties of sunscreen have been challenged by results of epidemiologic studies. These findings showed that sunscreen use was associated with an increased, not a decreased, risk of cutaneous melanoma.3,4 Results of recent studies of sunscreens have failed to show any link between the SPF and the prevention of skin nevi.5
Epidemiologic data suggest that behavioral issues could be involved in this association between high-factor sunscreen and melanoma. In one double-blind, randomized trial, people who used higher SPF sunscreens during intentional sun exposure, such as sunbathing, were exposed to the sun for a longer period of time. 6 The ability of sunscreen to delay sunburn occurrence probably encouraged people toward longer exposure. Increasing the quantity of sunscreen applied to the skin may also have this effect on people's behavior.
Sunscreen use was associated with an increased, not a decreased, risk of cutaneous melanoma
If the use of high SPF sunscreen leads people to stay longer in the sun, and possibly increases the risk of melanoma, is it still wise to use a sunscreen ?
In situations of non intentional sun exposure, which occurs during daily life, the answer is “yes.” Skin areas usually exposed in this way are the head and neck, the hands, and the forearms. Such exposure occurs during outdoor activities such as gardening and skiing. The trunk is rarely involved.
Several randomized trials have shown that the use of high SPF sunscreen during non-intentional exposure reduces the occurrence of actinic keratosis and squamous cell carcinoma.7,8Regular sunscreen use during such exposure also reduces the risk of sunburn.9 It is therefore possible that sunscreen use during non intentional exposure may reduce the risk of melanoma, although this hypothesis remains unproven. As discussed, the use of high SPF sunscreen does not protect against sunburn during intentional sun exposure.6,10It therefore seems unlikely to offer protection against melanoma in this situation.
So how should we advise people ? In everyday outdoor life, sunscreen is a useful part of a global strategy of sun protection. This strategy includes staying clothed and covered and taking steps to reduce time spent in the sun.Sun seekers who insist on indulging in intentional sun exposure should be warned that sunscreen use could involuntarily increase their exposure, especially if they use a high SPF sunscreen product.
Figure 1.
If he's wearing high SPF sunscreen, he may be increasing his risk of melanoma
Competing interests : None declared
West J Med 2000 ; 173 : 58
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