Does sunscreen expire? Everything you need to know about the shelf life of your favorite SPF

Now that summer's nearing and outdoor fun is beckoning, it's time to take stock of your sunscreen. (Though, you are wearing it 365 days a year, right ?) You might have a perfectly good-looking tube that seems totally fine — but does sunscreen expire? It does, and looks can be deceiving. When it comes to sun protection, taking that gamble has real consequences.

Unlike a vitamin C serum that oxidizes quickly or a mascara that starts to smell funky, expired sunscreen may not be so obvious. It most likely won't burn your skin or turn a strange color, but instead will simply stop working. Given that SPF is your primary defense against UV-induced skin damage, premature aging and skin cancer, it is a problem worth taking seriously. "Using expired sunscreen gives a false sense of security and can result in an unwanted sunburn, sun damage or worse," New York-based esthetician and certified cosmetologist Olga Skydan previously told our Senior Beauty Editor Jennifer Romolini .

The FDA requires sunscreen manufacturers to guarantee stability and efficacy for a minimum of three years , which is why most bottles carry an expiration date. If yours doesn't have one, the three-year rule from the date of purchase applies (grab a Sharpie and write it on the packaging or box to keep track). Still, expiration dates are only part of the story. Over time, the active ingredients in sunscreen actually begin to degrade. Obviously, this isn't good news for UV protection. "Heat exposure, like keeping it in your car or beach bag, speeds this up," said Dr. Rebecca Small, a board-certified physician and founder of RSMD Medical Aesthetics. (So, you might think twice about storing that bottle of sunscreen in your car, no matter how convenient.)

Which lasts longer: mineral or chemical sunscreen?

Both break down over time — just not equally. Chemical filters like avobenzone and octinoxate are particularly unstable and degrade with UV exposure (the very thing they're supposed to protect you from). Avobenzone, one of the most widely used UVA filters in the U.S., can lose a significant chunk of its potency (50-90%) after an hour of sun exposure without stabilizers present in the formula. Mineral filters like zinc oxide and titanium dioxide hold up better and are generally considered the more stable option. That said, they're not immune to formula degradation — surrounding ingredients can oxidize, and improper storage accelerates the process regardless of filter type. So while mineral sunscreens have the edge on stability, the real villains in both cases are heat and time.

How to tell if your sunscreenhas expired

Once you've cracked open a bottle, you might find yourself wondering exactly how long you've got. Some of your sunscreens may carry a Period After Opening (PAO) symbol, which is the little open-jar icon with a number followed by an "M," like "12M" or "24M." This tells you how many months the formula stays effective after opening. Others won't have it at all, and that's not a mistake — the FDA doesn't require it on U.S.-market products. If yours doesn't have one, the general rule among experts is 12 months from the day you first open it.

Your sunscreen will sometimes tell you when it's done, regardless of any date on the label. If it has changed in texture, color or smell, replace it immediately. And honestly, if you're applying sunscreen every single day — a shot glass' worth for the body, a quarter teaspoon for the face — you shouldn't have much left to worry about anyway.

With all that in mind, here are some sunscreens to keep your skin protected and nourished.