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FAQ: Is Sunscreen Toxic? And Other Questions, Answered

While most experts agree that you should use sunscreen year-round to prevent damage from the sun, harmful ultraviolet rays are strongest during late spring and early summer. We’ve partnered with health reporters from Wirecutter, The New York Times site that reviews and recommends products (and publishes annual ratings of sunscreens for the face and body), to answer some of the most common questions readers have about sunscreen, including how safe and effective it is, how to use it properly, and how to pick the right one for you.

No. In fact, it can mitigate a lot of potential damage from the sun, which can lead to premature skin aging and increased risk of skin cancer. However, experts have acknowledged that some people may be concerned about past evidence that has shown that some of the active ingredients in many sunscreens sold in the United States can reach the bloodstream and remain there for days.

“We don’t know what the health implications are yet, or even if there are any,” said Dr. Jenna Lester, an assistant professor of dermatology at the U.C.S.F. School of Medicine, “but we want to give credence to people’s concerns.”

Keep in mind that sunscreen is just one of many topical products whose potential health effects are not completely understood. “Of course it’s very alarming when people think there’s a chemical being absorbed by their skin and detectable in blood,” said Dr. Belinda Tan, a dermatopathologist in Torrance, Calif., “but we put a lot of things on our skin — lotions, cosmetics, fragrances — and studies aren’t done on whether or not those ingredients are detectable, so we need to step back and put the sunscreen conversation in context.”

If you’re concerned about the possibility of sunscreen chemicals seeping into the bloodstream, consider using those that contain either or both zinc oxide and titanium dioxide as their active ingredients, which have not been found to reach the blood.

Sun protection factor (SPF) is a measure of how well a sunscreen protects against sunburn, which is most often a result of exposure to ultraviolet B (UVB) rays, the type that cause most skin cancers. Most dermatologists, as well as the American Academy of Dermatology, recommend an SPF of at least 30 for most people and most climates. “There’s no harm in going higher, though,” especially for people whose skin burns easily or who have sun-exposure allergies, said Dr. Vinod Nambudiri, a dermatologist at Brigham and Women’s Hospital in Boston.

Once you go past SPF 30, the protection is more incremental than you may think when looking at the numbers on the bottle. When properly applied, for instance, an SPF 30 sunscreen shields skin from around 97 percent of the sun’s UVB rays, while an SPF 50 protects against roughly 98 percent. No sunscreen blocks 100 percent of the sun’s rays.

Most of the experts we spoke with said that more important than the actual SPF is finding a broad-spectrum sunscreen — one that protects against both UVA rays (which mostly cause skin aging and wrinkles) and UVB rays — that you enjoy wearing and can afford to consistently use and reapply. “Most people aren’t getting the SPF benefit on the sunscreen’s label because they aren’t applying a thick enough layer to their skin, and they usually aren’t reapplying often enough — usually every 80 minutes or two hours, depending upon the formula,” Dr. Tan said.

The average adult needs about one ounce of sunscreen to cover all exposed skin. “We often say a shot glass of sunscreen for the whole body,” Dr. Lester added, “but I tell my patients to fill the shot glass up to the brim and use even more if needed so you don’t miss any spots.”

Yes; in fact, it’s recommended. “Whether it’s sunny or cloudy, UV rays are present 365 days a year, and I encourage my patients to use sunscreen year-round,” Dr. Nambudiri said.

While it is not necessary to wear sunscreen on body parts that aren’t exposed to the sun (usually because they’re covered by clothing), it’s important to apply it to the face, ears, hands, forearms, neck and other often-exposed body parts to help prevent sun damage.

The best sunscreen for you is the one that you will apply (and reapply) often, but there are pros and cons to each type. Physical (or mineral) sunscreens reflect UV rays away from your skin, while chemical ones absorb UV rays so that your skin does not.

One pro of mineral sunscreens is that their active ingredients — zinc oxide and titanium dioxide — haven’t been shown to absorb into the blood. “If you’re a person who is concerned about the potential safety of applying chemical sunscreen to your skin and you also want the benefit of protecting your skin from harmful effects of UV rays, I would say mineral is best,” Dr. Tan said.

Mineral sunscreens, however, “are generally more expensive and less cosmetically elegant than chemical ones,” said Dr. Lawrence Eichenfield, chief of pediatric and adolescent dermatology at Rady Children’s Hospital-San Diego. Mineral sunscreens tend to take longer to rub in and appear chalkier than chemical ones, which tend to rub in easier, feel less noticeable on and blend in better with the skin.

“People who don’t like the way a sunscreen looks or feels are less likely to stick to consistent use,” said Dr. Lester, whose work focuses on skin color-related disparities in research and health care. In her own practice, she said, “brown-skinned individuals often avoid mineral sunscreens because they tend to leave a white cast on the skin.”

Wirecutter testing has found that chemical sunscreens with active ingredients including avobenzone, octocrylene and oxybenzone tend to feel lighter on the skin, rub in easier and appear less visible.

It can. “Certain ingredients in some sunscreens do contribute to coral reef damage,” Dr. Lester said.

Oxybenzone, octocrylene and octinoxate are among the primary sunscreen ingredients of concern. The only two “reef-safe” active ingredients approved by the Food and Drug Administration are “non-nanotized” zinc oxide or titanium dioxide. (A non-nanotized ingredient means that it is 100 nanometers in diameter or more.)

However, no sunscreen is known to be totally safe for aquatic life, so the best way to protect yourself and the environment is to cover as much of your body as possible with UPF (ultraviolet protection factor) clothing (though you’ll still need to use sunscreen on exposed skin).

Avoiding the sun (especially between 10 a.m. and 4 p.m., when the sun’s rays are strongest) is one excellent way to protect your skin from sun damage. So is wearing protective clothing, like long-sleeved shirts and wide brimmed hats. Alternatives like sunscreen pills or supplements “are being studied right now,” Dr. Nambudiri said, but none are approved by the F.D.A. and there is no evidence that they are safe and effective.

While the two terms are often meant to refer to the same thing in conversation, you shouldn’t see the word “sunblock” on labels at all. The F.D.A. banned its use on approved sunscreens in 2011, considering it to be an overstatement of effectiveness since no sunscreen can block UV rays completely. The agency similarly does not allow the terms “waterproof” and “sweatproof.”

Yes. “It’s a misconception that darker skinned people can’t get skin cancer,” said Dr. Nambudiri. Even though darker-skinned people may not burn as quickly as fairer-skinned people, it doesn’t mean their skin isn’t experiencing deleterious effects from the sun’s rays. “Sunburns, aging, uneven skin tone and hyperpigmentation are all problems that can be exacerbated by sun exposure in dark-skinned people,” Dr. Lester said.

There’s no real consensus on whether you should apply sunscreen before or after you apply makeup or skin care products like moisturizer, but if you lather up with sunscreen first, make sure that it has fully absorbed (it should feel mostly dry to the touch) before you apply anything else. It’s also important to apply sunscreen even if you’re using foundations or powders with SPF built in, since these products may not provide consistent sun protection.

Make sure to reapply sunscreen every two hours (or more frequently, especially after sweating or swimming), even if you’re wearing makeup. This may require reapplying sunscreen on top of it. There are plenty of options for on-the-go sunscreen reapplication, including sunscreen sticks or sprays (though you still need to rub these in). You could also use a makeup sponge to dab on your favorite sunscreen in an even layer over your makeup.

Caira Blackwell contributed reporting.

Interested in learning more about the best things to buy and how to use them? Visit Wirecutter, where you can read the latest reviews and find daily deals.

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