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Smart move to slather on the SPF to safeguard skin from the sun's aging and skin-cancer producing rays. But you may notice that your skin has become angry since then. If you're experiencing burning or stinging or seeing a rash, you may be allergic to your favorite sunscreen, says Sawlani. "This is something we see occasionally in our clinic," she says. Most often, people react to chemical-based sunscreens, she notes. But this isn't license to go without SPF. (Ninety percent of melanomas, a deadly form of skin cancer, are caused by UV light.) In those situations, Sawlani suggests switching to a mineral-based sunscreen that contains UV-blockers like zinc oxide or titanium dioxide.