10 Skin Cancer Mistakes Even Smart Women Make

8. Expired Sunscreen

The Mistake: You're still using the sunscreen you bought a few years ago.

Thrifty? Yes. Smart? No.

If you're outside a lot and a six-ounce bottle of sunscreen lasts you longer than a month, you're not using enough. You should slather on a half-ounce with every application; one ounce if you're wearing a swimsuit (that's about the amount that would fill two-thirds of a shot glass). Using too little means you're only getting a fraction of the protection promised on the bottle, because you're not putting a thick enough layer of sunscreen on your skin, warns Janice Stumpf, a clinical associate professor at the University of Michigan Health System and College of Pharmacy.