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Sunscreens Prevent the Development of Solar Keratoses

Regular use of sunscreens has increasingly been recommended to prevent the long-term effects of sun exposure -- including the development of skin cancers -- despite insufficient data on the efficacy of this practice. Researchers in Australia performed a randomized, controlled trial of the effect of daily use of a broad spectrum sunscreen on solar keratoses.

Five hundred eighty-eight subjects who each had at least one solar keratosis applied either sunscreen containing methoxycinnamate and dibenzoylmethane with an SPF of 17 (which blocks 94% of radiation in the 290 to 320 nm wavelengths and 90% of radiation in the 320 to 360 nm wavelengths) or a base cream once a day during the 7 sunniest months of the Australian spring and summer. Subjects were advised to avoid the sun and to protect themselves with hats and clothing. Three times during the 7 months subjects were examined for the development of new solar keratoses and the disappearance of previously existing ones. Four hundred thirty-one subjects completed the study.

During the study period, the mean number of solar keratoses increased by 1.0 per person in the base-cream group and decreased by 0.6 per person in the sunscreen group. Fewer new lesions appeared in the sunscreen group than in the base-cream group, with a rate ratio of 0.62. Of the lesions present at baseline, 25% disappeared in the sunscreen group, as compared with 18% in the base-cream group; after correcting for sex and skin type, the likelihood of remission was 1.53 times greater in the sunscreen group. The development of new lesions and the remission of existing ones correlated in a dose-response relationship with the amount of sunscreen used.

Comment: These results suggest that regular use of broad spectrum sunscreens is at least partially successful in preventing the development of solar keratoses, the precursor lesions of nonmelanoma skin cancer. By extrapolation, it seems reasonable to conclude that long-term, appropriate sunscreen use will prevent the development of nonmelanoma skin cancer. These investigators have previously shown that solar keratoses disappear spontaneously, especially in persons who reduce their exposure to sunlight. Combining sunscreen use with sun avoidance appears to both reduce the number of existing solar keratoses and decrease the development of new lesions. This information is of great practical significance for public health prevention and can be used by dermatologists in efforts to convince patients to limit sun exposure and increase sunscreen use.

— JS Dover

Published in Journal Watch Dermatology November 1, 1993

Citation(s):

Thompson SC et al. Reduction of solar keratoses by regular sunscreen use. N Engl J Med 1993 329 1147-1151.

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