In a randomized, controlled trial of the effect on solar keratoses of daily use of a broad-spectrum sunscreen cream with a sun-protection factor of 17 in 588 people 40 years of age or older in Australia during one summer, the subjects applied either a sunscreen cream or the base cream minus the active ingredients of the sunscreen to the head, neck, forearms and hands . The mean number of solar keratoses increased by 1.0 per subject in the base-cream group and decreased by 0.6 in the sunscreen group (difference, 1.53; 95% confidence interval, 0.81 to 2.25). The sunscreen group had fewer new lesions (rate ratio, 0.62; 95% confidence interval, 0.54 to 0.71) and more remissions (odds ratio, 1.53; 95% confidence interval, 1.29 to 1.80) than the base-cream group. There was a dose-response relationship.