 And both cause cancer. But the perfect sunscreen doesn't count if you use it wrong. Don't need sunscreen on a cloudy day? Wrong. 80% of UV rays still get through the haze. Only use sunscreen at the beach? Nope. Anytime you're outside, UV rays attack the skin, so you need protection. And you have to reapply sunscreen every two hours. Remember, SPF plus broad spectrum equal healthy fun in the sun.