Does sunscreen expire? What to know to protect your skin against UV rays this summer.

As the Sun gets brighter and temperatures warm up, you may want to soak up some rays and enjoy your time outside. Whether you're hitting the beach or sitting on your lawn, it is crucial to protect yourself from the Sun's UV rays.

One key tool for preventing sunburn and other skin damage is sunscreen. Before you grab that old bottle sitting in the back of the closet and lather up, you may want to check if it's still good. But can sunscreen expire?

With the summer season and outdoor activities quickly approaching, here are important tips to keep in mind when using sunscreen.

Does sunscreen expire?

Sunscreen does have an expiration date.

Due to FDA regulations, sunscreens are required to have an expiration date unless testing by manufacturers can guarantee its longevity and stability past a certain date. Most sunscreen should have an expiration date listed on its packaging.

How long does sunscreen last?

If your sunscreen does not have an expiration date, its shelf life is about three years after purchase, according to the FDA. Sunscreen without an expiration date is considered expired three years after purchase.

For sunscreen without a listed expiration date, mark the purchase date. You can continue using it until three years after buying it. After then, the sunscreen should be discarded since it is no longer guaranteed to be fully effective or usable, according to the FDA.

For proper storage, keep sunscreen away from excessive sunscreen ever expire or direct sun, according to the Mayo Clinic. When brought outside, make sure sunscreen is kept in the shade or wrapped in a towel. If the sunscreen has changed consistency or has drastic changes in color, you should throw it away, according to the Mayo Clinic.

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How does sunscreen work?

Sunscreen's active ingredients prevent the Sun's UV rays from getting to your skin, according to the Skin Cancer Foundation. Minerals – like titanium dioxide and zinc oxide – help block the Sun's rays, while ingredients like avobenzone and octisalate absorb UV rays before they can harm the skin.

The SPF, or sun protection factor, determines how long it will take for the Sun's rays to affect your skin when applied in comparison to bare skin. For example, with SPF 50, it would take you 50 times longer to burn.

If you plan on being outside for long periods of time, it is recommended to use SPF 30 or higher, according to the Skin Cancer Foundation. For waterproof or water-resistant sunscreen, it is important to reapply since no sunscreen is completely waterproof; it eventually washes off.

In general, you should reapply every two hours, according to the Skin Cancer Foundation. You should also reapply immediately after swimming or excessive sweating.

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This article originally appeared on USA TODAY: Does sunscreen expire? Here's how long it lasts, plus UV, SPF tips.