Daily use of sunscreen slows the acquisition of solar keratoses, whereas daily doses of beta carotene have no effect on development of the skin lesions, according to an article in the April issue of The Archives of Dermatology.

According to information in the article, the presence of solar keratoses is one of the strongest predictors of skin cancer. The risks for basal cell carcinoma and squamous cell carcinoma are increased 3-fold to 12-fold in the presence of solar keratoses.

Steven Darlington, B.Sc., and his Australian colleagues designed the current study to evaluate whether controlling development of the benign skin lesions might reduce the risk of skin cancer.

A total of 1,621 adults ages 25 to 74 years were randomized to daily use of sunscreen (applied to the head, neck, arms, and hands every morning) or application of sunscreen at their own discretion. The participants were also randomly assigned to take 30 mg beta carotene or placebo daily. The study was conducted between 1992 and 1996.

The researchers found that the ratio of solar keratosis counts in 1994 relative to the start of the study in 1992 was lower in people randomized to daily sunscreen than in those randomized to discretionary use. The researchers wrote that the 24 percent reduction is equivalent to the prevention of an average of 1 additional lesion per person over that time period.

No effect was found on the rate of change of solar keratosis counts in participants on beta carotene supplementation compared with those on placebo.

"Our study found that the number of prevalent solar keratoses increased over the course of the trial in all groups, consistent with the rapid accumulation of solar keratoses in adults of this age living in a subtropical environment," wrote the authors. "Despite this, requesting a random half of participants to apply sunscreen daily resulted in a decrease in their average rate of solar keratosis acquisition, especially in the first 2.5 years of the trial."

In an accompanying editorial, John L. M. Hawk, M.D., wrote: "The study indicates yet again the great potential value of cutaneous sunscreen application, when undertaken conscientiously and carefully, against the now extremely well-documented ravages of sunlight in both the short and long term."

"This splendid randomized controlled trial is the continuation of a previous one showing sunscreen efficacy against the development of squamous cell carcinoma. It provides further evidence in a very large number of adults (1,621 subjects aged 25-74 years), over a reasonably long time (2.5 years), in a very ultraviolet-intense environment (Queensland, Australia), that frequent, liberal applications of high-protection sunscreen by ordinary people under normal circumstances is 25 percent more efficient against the development of potentially premalignant actinic keratoses than ad hoc applications."