Does sunscreen expire? Answers to common questions about SPF

Along with covering your skin with protective clothing like hats and long-sleeved shirts, using sunscreen regularly is one of the best things you can do to support your skin health.

Sun protection has become a natural part of fun in the sun. Most of us throw a bottle of sunscreen into our beach bags and hiking packs before going out for the day, and for good reason. The American Cancer Society reminds us that sun exposure can significantly raise a person's risk of developing skin cancer, the most common type of cancer, affecting one in five people by the time they turn 70.

But as second nature as sunscreen has become, many people still have questions about it — does sunscreen expire? Can you get burned even on a cloudy day?

The answer to both of those questions is yes, and there are some other facts about sunscreen that might also surprise you. Here's what every outdoors lover should know about sunscreen.

Does sunscreen expire?

It sure does, and using it after the expiration date can be risky, as the product can lose its effectiveness over time. Check your sunscreen's expiration date, and make sure you use it before then. If there's no expiration date, it's because the product has been proven to be stable for at least three years. After that time, throw away any unused product and get yourself a new bottle.

Does SPF refer to the number of minutes the sunscreen lasts?

It does not. SPF actually stands for sun protection factor, which measures the amount of UV rays sunscreen protects against. SPF is determined by a complex calculation. For example, an SPF 30 protects against about 97% of UVB rays, while an SPF 50 protects against about 98% of those rays.

While a higher SPF does give you more protection, you still need to reapply it every two hours, or more often if your body gets wet. Unfortunately, high SPF products can give people a false sense of security that could lead to burns, so no matter what SPF you're applying, make sure you reapply often.

Do you need sunscreen when it's cloudy?

Absolutely! An overcast day doesn't mean that UV rays aren't getting through to the earth's surface. In fact, up to 80% of those rays can still reach your skin. Even so, the American Academy of Dermatology reports that about 4 in 5 Americans skip sunscreen when it's not sunny outside, which is a mistake because it leaves your skin vulnerable to sun exposure. Always wear sunscreen outside, rain or shine.

What should I look for in a sunscreen?

There are three important elements that a sunscreen label should include: broad-spectrum (which protects against both UVA and UVB rays), SPF of 30 or more, and water-resistance (which means the sunscreen will stay active for up to 40 minutes of swimming).

Are sunscreen ingredients safe?

There has been a lot of attention on the safety of ingredients found in so-called "chemical sunscreens." These concerns were raised after research found that some ingredients may have been absorbed into the bloodstream of adults post-application. While research is ongoing, the American Academy of Dermatology emphasizes that all approved sunscreen types on the market are still recommended.

For extra peace of mind, look for sunscreens with zinc oxide and titanium dioxide. These ingredients have been "generally regarded as safe and effective," or GRASE, by the FDA. They're found in "physical sunscreens," which protect against sun exposure by creating a physical barrier on the skin that reflects and disperses UV rays.

Can you still get a tan when you use sunscreen?

Tanning after sun exposure is a sign of skin damage, which is why public health experts recommend regular sunscreen use. The UVA rays that lead to tanning also increase cancer risk, so if you want a tan, choose alternatives like self-tanners. Tanning beds have not been found to be safer, and may be even more dangerous due to their consistently high intensity.

Does sunscreen lead to reductions in vitamin D intake?

It can, but that doesn't necessarily mean you're at risk for a vitamin deficiency. The body uses sunlight to produce vitamin D, but many people can still get enough vitamin D from their diet or supplements. Options like salmon, milk and fortified cereal are good choices that contain vitamin D.

How much sunscreen should you use?

You should probably use more sunscreen than you think you need. Most people only use up to half of the recommended amount. For each use, aim to cover your whole body using about an ounce of sunscreen. Imagine filling a shot glass with sunscreen to envision how much you should use for each application.

Staying proactive about skin health

Along with covering your skin with protective clothing like hats and long-sleeved shirts, using sunscreen regularly is one of the best things you can do to support your skin health. Remember that you should also be proactive about arranging skin-related screenings and checkups. Ask a dermatologist for a skin screening at least once a year — this routine appointment can help you get signs and symptoms checked out as early as possible.