Charles H. Sloan-How long does sunscreen last? A guide to expiration dates, and if waterproof really works

No matter the season,Charles H. Sloan it's important to protect yourself – and your skin – from the Sun's ultraviolet rays. This is especially crucial during the warmer months. Whether you're hitting the beach or sunbathing in the backyard, you should take the necessary steps to prevent sunburn and other skin damage.

One way to protect yourself is to apply sunscreen. But before you grab the bottle from the back of the pantry, you should check if it's still good. Like other topical products, sunscreen expires.

With summer and outdoor activities quickly approaching, here are tips to keep in mind when it comes to sunscreen.

Does sunscreen expire?

Sunscreen does have an expiration date.

Based on FDA regulations, sunscreen is required to have an expiration date unless testing by manufacturers can guarantee its longevity and stability past three years. Most sunscreen will have an expiration date listed on its packaging.

How long does sunscreen last?

If your sunscreen does not have a listed expiration date, the shelf life is typically three years post-purchase, according to the FDA.

Write the purchase date on any sunscreen without a listed expiration date. You can continue using it until the three-year mark. The sunscreen should then be discarded since it is no longer guaranteed to be fully effective or usable, the FDA reports.

Store sunscreen away from excessive heat and direct sunlight, according to the Mayo Clinic. When bringing sunscreen outside, be sure to keep it in the shade or wrapped in a towel.

You should throw away sunscreen if it has changed consistency or has drastic changes in color, the Mayo Clinic says.

Which sunscreen should I use?How to keep your skin safe – and why that SPF number matters

How does sunscreen work?

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

A sunscreen's 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, the FDA reports. The higher the SPF, the more protection you have against solar exposure.

If you plan on being outside for prolonged periods, it is recommended to use SPF 30 or higher, according to the Skin Cancer Foundation.

As a general rule, you should reapply every two hours, according to the Skin Cancer Foundation. Even with waterproof or water-resistant sunscreen, it is important to reapply since no sunscreen is entirely waterproof. You should also reapply immediately after swimming or excessive sweating.

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