Sunscreen with a sun protection factor (SPF) of at least 15 helps reduce the risk of malignant melanoma, a Norwegian study in the Journal of Clinical Oncology has confirmed.
It followed 144,000 women, ages 40 to 75, for a decade and found that those who regularly used sunscreen with SPF 15 or higher were one-third less likely to develop melanoma, the most dangerous type of skin cancer, than those using weaker sunscreen. The FDA allows only broad-spectrum sunscreens with SPF 15 or higher to claim they help protect against skin cancer. ("Broad-spectrum" means that a sunscreen protects against ultraviolet A rays as well as ultraviolet B.)
See also Sunscreen Myths vs Facts.