Patients who were younger than 55 years were randomly assigned to a group asked to apply sun-protection factor 15+ sunscreen to their head, neck, arms, and hands each morning and after bathing, after spending more than a few hours in the sun, or after sweating heavily or to a group asked to use sunscreen at their discretion. Participants were also randomly assigned to receive daily β-carotene or placebo pills. Impressions were taken of the backs of participants’ hands at the beginning of the study and 4.5 years later. The impressions were examined for microscopic changes of skin aging by assessors who did not know to which study groups the participants had been assigned.