We've all been there: you're headed out for a day at the beach and you're staring at the many sunscreen bottles you've stashed away over the past few years. You likely can't remember where they all came from or how long they've been sitting in your hall closet, and you're asking yourself, "Is it OK to use expired sunscreen?"

The Shelf Life of Sunscreen

Sunscreen does, in fact, expire. Though you might get away with ignoring the "best before" date on some products' packaging, you shouldn't overlook the expiration date on sun protection products.

Sunscreen is made up of a mix of active and inactive ingredients. The active ingredients, such as zinc oxide and avobenzone, protect your skin from the sun's harmful rays, as noted by the U.S. Food and Drug Administration (FDA). Over time, these ingredients can start to break down. When they do, they no longer do their job.

The expiration date on sunscreen tells you when the product may no longer be effective. The FDA requires that all manufacturers perform stability testing on nonprescription drugs, including sunscreen.

Generally, the shelf life of sunscreen is approximately two years with a maxiumum shelf life of up to three years. So, if your sunscreen doesn't have an expiration date, you'll want to toss it three years after purchase.

The truth is that if you're applying as much as you actually need on a regular basis, you should work your way through your sunscreen stash pretty quickly.

Can You Use Last Summer's Sunscreen?

Or even sunscreen from two summers ago? Maybe.

If the sunscreen is past its expiration date, the American Academy of Dermatology (AAD) recommends throwing it out. There's no easy way to tell just how much the active ingredients have degraded, and the product may not effectively protect you from damaging ultraviolet rays.

It's important to note that not all sunscreen comes with an expiration date printed on the bottle. If you find a bottle at the bottom of an old beach bag and can't recall when you bought it, open a new one to be safe.

You can also check the product and look for visible signs that it may have gone bad. If the sunscreen has changed color, the consistency is off, or it has a funny smell, don't use it—even if the expiration date hasn't passed. According to the Cleveland Clinic, physical or mineral-based sunscreen will feel gritty to the touch whereas chemical-based sunscreen may become watery.

If you only have an old bottle of sunscreen and can't get more, be sure to take extra sun protection precautions. Given that using expired sunscreen may not offer the same level of protection, you may put yourself at risk for sunburn and, ultimately, skin cancer. Limit your exposure to the sun—especially during the middle of the day—wear protective clothing like long-sleeved shirts and hats, and stick to the shade.

How to Store Sunscreen Properly

Although expiration dates give you an idea of when to get rid of old sunscreen, it's not all you need to know. According to Consumer Reports, sunscreen's effectiveness also depends on how you store it.

Not only do the active ingredients naturally break down over time, but heat and humidity can speed up this process. Try to store sunscreen in a cool, dry area, not in your car or bathroom where it can overheat or be exposed to high moisture. As follows, avoid storing it in direct sunlight. If you're headed to the beach or park, the FDA suggests wrapping your bottles of sun protection in towels or keeping them in the shade. You can also toss them in a cooler if you have one.

Don't worry about cracking open a new bottle either, as opening a container of sunscreen doesn't make it expire faster. Expiration dates start from the time of production, not from the time of opening. Further, Consumer Reports tested open samples from previous years that were stored properly and didn't find any difference in performance. So go ahead and use up the half-empty bottles, as long as their dates haven't passed.

Finally, if you purchase sunscreen that doesn't have an expiration date printed on the container, the AAD suggests writing the date of purchase on the container with a permanent marker. That way, you'll know when it's time to restock your supply of sun protection.

So if you're still wondering if it's OK to use expired sunscreen, know that it's always best to play it safe and use a product still in its prime.