SummaryApplication of sunscreen to the skin is widely used as an adjunct strategy, along with wearing protective clothing and seeking shade, to protect against skin cancer and photoaging that result from excessive sun exposure. Many epidemiological studies of case–control and cohort study design have studied the effects of sunscreen use on skin cancer, and more recently photoaging, but their findings have been mostly uninformative. This review of results of randomized controlled trials shows that the evidence, though limited, supports beneficial effects of sunscreen application on the occurrence of skin cancers and skin photoaging.