When and How Much Sunscreen Should You Reapply, According to Experts

Health Canada’s standard advice calls for a broad-spectrum sunscreen with at least SPF 30, applied 15 minutes before heading outdoors and refreshed every two hours. Dermatology leader Dr. Cheryl Rosen points out that the rule can be relaxed when people are inactive, like sitting under a tree, and that winter activities such as skiing generally only require facial application. She adds that summer pursuits involving water or heavy perspiration still merit regular reapplication.

Sunscreen entrepreneur Lisa Heggie says the one-teaspoon-per-area guideline helps but isn’t universal; body size, exposed skin and protective clothing affect the needed amount. She also warns that aerosol sprays may miss spots, especially in wind, and suggests using lotion and applying it in two light coats for uniform protection.