How Much Sunscreen Do You Really Need?

Your sunscreen might have a dark secret: Unless you’re slathering liberal amounts of the lotion on your face, arms, and neck this summer, you could be leaving your skin more exposed than you think.

Both the Centers for Disease Control and Britain’s National Institute for Health and Clinical Excellence recommend using a sunscreen with an SPF of at least 15.

But unless you’re spreading 2 milligrams of lotion onto every square centimeter of exposed skin, you’re likely getting just a fraction of the sun protection listed on the label, according to a report from the Drug and Therapeutics Bulletin, a company that conducts independent evaluations of medical treatments.