The old rule about using a shot glass worth of sunscreen every time you apply still holds up, says Dr. Graf. (That's about 1.5 ounces.) But now that more of us are opting for continuous spray formulas, it can be hard to tell if we're really getting enough coverage. To make sure you're using sprays correctly, she suggests holding the can six inches from skin and spraying nonstop, so you can see the moisture covering the entire area. "Then rub it in—yes, even if the bottle says you don't have to—so you don't miss spots," Dr. Graf says. "And repeat the spray a second time."