Your Burning Questions on Sunscreen, Answered by Dermatologists

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Finding a sunscreen that works for your specific skin type and offers credible, trusted ingredients, is your best defense when lounging on the beach or poolside. But before you go on a shopping spree to stock up, take a moment to consider what sunscreen actually does and how it works. While you already know you should be using it daily, you’ve probably wondered how long it really lasts. Or if you can tan through sunscreen. Or if it does more harm than good on your little one. Luckily, dermatologists have broken down all of your burning questions so you can enjoy those summer days without worrying about sunburn.

How does sunscreen work?

This depends on what type of sunscreen you’re using, according to dermatologist Dr. Angela Lamb. Some sunscreen products feature active ingredients that create a firm barrier from the sun, while other ingredients absorb UV rays instead of blocking them. Mineral or physical sunscreens feature zinc oxide and titanium dioxide, which physically block the sun, while active ingredients octyl methoxycinnamate (OMC) and oxybenzone, usually found in chemical sunscreens, absorb UV rays. Both will work to protect your skin.

What is sun protection factor (SPF), and what do those numbers mean?

SPF stands for “sun protection factor” and it measures the level of protection against UVB rays, or the rays responsible for sunburn. According to dermatologist and member of the MDSolarSciences Scientific Advisory Council, Dr. Diane Berson, an SPF 15 covers 93 percent of UVB rays, SPF 30 covers 97 percent, SPF 50 covers 98 percent. Sunscreen brands use independent testing companies to test the SPF levels in their products in compliance with the FDA testing guidelines.

“Before the FDA introduced its new labeling requirements a few years ago, SPF levels caused a lot of confusion for customers,” explains Dr. Berson. “Some people thought that the SPF number corresponded to the number of minutes the sunscreen protected the skin, the percentage of rays the sunscreen filtered or other misguided logic. The SPF number theoretically correlates to how long a person can stay in the sun without burning. For example, when wearing an SPF 30, you can remain outside for 30 times longer than if you were unprotected. However, that doesn’t take into consideration your skin type, any toweling, swimming, sweating or the level of the UV index that particular day.”

Keep in mind that the SPF of a sunscreen product does not cover UVA rays, or the rays responsible for premature skin aging. To protect your skin from both UVA and UVB rays, choose a sunscreen that says “broad-spectrum” on the label. “When choosing a sunscreen, make sure that you’re choosing a product that has been tested for broad-spectrum protection (protects from both UVA and UVB). That way, you’ll be protected not only from the immediate effects of sun damage (sunburn) but also from long-term damage that shows up as wrinkles, sunspots and worse—skin cancer,” Dr. Berson says.

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Does sunscreen prevent tanning?

Fun fact if you think you must use a (super-dangerous!) tanning oil to get that sun-kissed glow: Dr. Lamb says you can get a tan from using sunscreen. The only catch is that it will be at a much slower rate than if you weren’t wearing sunscreen. How can you still get those freckles and tan lines even if you’re reapplying? Dr. Lamb explains that there is no sure-fire formula that can protect against 100 percent of UV rays.

Why did the FDA limit the SPF to just 50? What’s wrong with sunscreens higher than 50?

According to Dr. Berson, while there is a fairly big difference between an SPF 15 and 30, the difference in coverage lessens considerably between SPF 30 and SPF 50. Protection afforded by products over SPF 50 is only incremental. “Since an SPF 50 protects from 98% of UVB rays and nothing offers 100% protection, there is no statistical significance to using an SPF over 50. Products with higher SPF values may be misleading and give consumers a false sense of security,” she explains. “When customers see a product marketed as an SPF 100+, some may think that means they’re protected from 100% of the UVB rays, or that the product will work all day. There’s no such thing as a total sunblock—and all products must be reapplied in accordance with the FDA guidelines.”

How long does sunscreen last, and how often should I reapply?

Though many factors might contribute to how long sunscreen protection lasts—from the level of UV index to whether you’re sweating or swimming—as a general rule of thumb, experts recommend reapplying your sunscreen every two hours.

“With the new FDA regulations, it’s much easier for people to understand the need to reapply at least every two hours, and every 40 or 80 minutes while swimming or sweating. These directions are now easily seen on the packaging,” says Dr. Berson.

When can babies wear sunscreen?

Heading to the pool with your little guy but not sure how to protect his virgin skin? Dr. Lamb says it’s not recommended for newborns to wear sunscreen until they’re at least six months old. However, if you’re spending time strolling around under the hottest time of day, she suggests layering on hats, sunglasses and clothing. Once they’re old enough, consider sunscreens specifically designed for babies and to reapply sunscreen more often just to be safe.

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What sunscreen ingredients should you avoid?

While everyone has a varying preference on using traditional sunscreen options versus the more natural alternatives, there are certain words on the back of that label you should search for before when heading to check out. What are they? According to Dr. Lamb, “parabens” and “formaldehydes” can be problematic to sensitive skin.

Does sunscreen block vitamin D?

Sunscreen does not fully block vitamin D but it may lower absorption of vitamin D, according to dermatologist Dr. Robin Evans, MD. If you’re concerned about a deficiency, she suggests taking a blood test that will quickly tell you if your levels are low. If they are, she suggests taking a supplement, rather than exposing yourself to dangerous rays. “We know that sun exposure is linked to skin cancer; better to take vitamin D as a supplement and then limit one’s sun exposure to decrease your risk for skin cancer,” she notes.

Does sunscreen have an expiration date?

Just like most beauty products, sunscreen also has an expiration date for when they should be used or thrown out, so check the bottle to determine if and when you need to replenish. As skin care products tend to deteriorate once opened, remember to replace your used sunscreen two years after it’s been opened—even if the expiration date on its label says otherwise—to make sure you’re getting the utmost protection. “While expired sunscreen won’t damage your skin, you should use sunscreen before it expires for the best results and ultimate protection,” Dr. Lamb recommends.

Is spray sunscreen or lotion better?

Here’s the kicker: both spray and lotion work perfectly fine, but only if they’re applied appropriately. So if you’re haphazardly pulling a spray bottle out of your beach bag and lazily spritzing it across your body, you’re likely not getting the same protection that you receive when you massage your lotion vigorously until it’s completely rubbed in.

From her professional standpoint, Dr. Evans always prefers a lotion over a spray: “Creams and lotions will offer better protection than sprays. A spray, of course, is better than nothing, but these formulations offer inferior protection,” she says.

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Does do-it-yourself sunscreen work?

If you’re thinking of mixing up your own cocktail of sunscreen to try and budget for an extended beach vacation, Dr. Lamb says to think again. “I do not believe in DIY sunscreen. It is unsafe and impossible to know if you are getting the correct amount of the zinc or titanium dioxide when you make it yourself,” she explains.

However, instead of making beauty products at home, says Dr. Evans, you can protect yourself from the sun using clothing. She also adds that having a healthy amount of antioxidants in your diet will help prevent sun damage, too. Another piece of good news? If you’re not a fan of the traditional gooey cream that leaves a white cast on your skin, new sunscreen formulas—from powders to sticks to setting sprays—are not only just as effective but are also convenient enough to tote around and reapply wherever, whenever!

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