Still have a bottle of sunscreen in your bathroom closet from last year? While you might assume you need toss is out and buy a new one, sunscreen actually lasts longer than you think. Check the expiration date (if there is one)—but you’ve got three years from the date of purchase to use it up.How to know if your sunscreen has expiredThis advice comes straight from the FDA, which asks sunscreen makers to put an expiration date on their product showing when it will stop providing the level of protection shown on the label. If there’s no date, that means testing showed it should be good for a full three years after purchase. (This is a longstanding rule that is not related to the current administration—it's been in place for years.) Sunscreen that is older than that may have lost its potency, but then again, maybe not. Because it’s a bit of a gamble, the FDA recommends tossing sunscreen that is past the three-year mark or past its expiration date. If there’s no expiration date, but you can remember buying it last year, or even two years ago, it’s still likely to be as good as new. If you find a bottle in your closet and you have no idea when you bought it, they recommend tossing it to be safe. How to make your sunscreen last the full three yearsExpired sunscreen may not look or feel any different from fresh, but if it does look different, that may mean it's gone bad prematurely. Sunscreen needs to stay in its original formulation to remain effective. For example, if it initially had the protective chemicals evenly suspended in the lotion but has since separated, it's not going to be as effective anymore. If you squeeze the bottle and what you get is a separated goo and liquid, it's probably not good anymore. The way you store sunscreen can affect how long it lasts. The FDA recommends, ironically, that we keep sunscreen bottles out of the sun. Extreme heat could cause the product to deteriorate early, so they suggest you leave your sunscreen in the shade or wrap it in towels when you’re at the beach. You can also put it in a cooler to be extra safe.