An illustration of a bottle of sunscreen.

You need sunscreen on a sunny spring day just as much as you do when you’re getting a little beach or pool time in the middle of July. But many people don’t think to stock up on sunscreen before the start of the summer season. Will what’s left in last year’s tube do the job?

Maybe. Sunscreen remains effective for three years, but it does expire, so check the date on the container and don’t use it if the date has past. 

However, not all containers carry a date. As long as the sunscreen has been formulated to stay stable for three years, the Food and Drug Administration doesn’t require one.

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If your sunscreen doesn’t have a date and you can’t remember when you bought it, you shouldn’t take a chance that it will still protect you. Buy a new bottle and use a permanent marker to write the date you purchased it on the container.

Even if your sunscreen “date” is current, whether it is still really effective also depends on how you’ve stored it.

“Heat and humidity can accelerate the breakdown of sunscreen,” says Susan Booth, who oversees sunscreen testing at Consumer Reports. “If the bottle is in your car or bathroom, the temperature fluctuations may have affected the product. But if it’s been kept at room temperature, you’re good to go.” Properly stored, a sunscreen that has an expiration date of six months away should work as well as one that has an expiration date of three years away. (Learn about the right way to wear sunscreen.)

This is true even if you have only half a bottle or so left over. “Opening a sunscreen, using some, and recapping it will not cause the sunscreen to go bad any faster,” Booth says. “We have retested sunscreen samples from the previous year’s testing after storing them in our lab and found no differences in performance.”

If the contents of the sunscreen have separated—“spoiled” sunscreen will be watery—or if it has changed color or has a funny smell, toss it even if it hasn’t yet expired.