While most experts agree that you should wear sunscreen year-round to prevent damage from the sun, harmful ultraviolet rays are strongest during the late spring and early summer.
The Times’s Well section partnered with Wirecutter, a New York Times Company that reviews and recommends products (and publishes annual ratings of sunscreens for the face and body), to answer common questions about sunscreen, including about how safe and effective it is, how to use it properly, and how to pick the right one for you.
How much SPF is enough?
Sun protection factor (or SPF) is a measure of how well a sunscreen protects against sunburn, which usually results from exposure to ultraviolet B (or UVB) rays, the type that cause most skin cancers. Most experts recommend an SPF of at least 30 for most people and most climates.
“There’s no harm in going higher, though,” especially if your skin burns easily or you 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 becomes more incremental. When properly applied, for instance, an SPF 30 sunscreen shields skin from about 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 experts we spoke with said that what’s more important is finding a broad-spectrum sunscreen — one that protects against both UVB and ultraviolet A (UVA) rays, which mostly cause skin aging and wrinkles — that you enjoy wearing and can afford to reapply and use consistently.
“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,” said Dr. Belinda Tan, a dermatopathologist in Torrance, Calif.
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,” said Dr. Jenna Lester, an associate professor of dermatology at the U.C. San Francisco School of Medicine, “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.”
Are there any alternatives to sunscreen?
Avoiding the sun (especially between 10 a.m. and 4 p.m., when its 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 Food and Drug Administration and there is no evidence that they are safe and effective.
Which type of sunscreen is better: chemical or physical?
Sunscreen can mitigate a lot of potential damage from the sun. However experts have acknowledged that some people may be concerned by past reports that active ingredients in many chemical sunscreens 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,” Dr. Lester said, “but we want to give credence to people’s concerns.”
The best sunscreen for you is the one that you will apply, and reapply, often.
Physical (or mineral) sunscreens reflect UV rays away from your skin, while chemical sunscreens 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 concerned about potential safety issues with chemical sunscreens but also want to protect your skin from harmful UV rays, “mineral is best,” Dr. Tan said.
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,” Dr. Tan said, “but we put a lot of things on our skin — lotions, cosmetics, fragrances.” It’s important to take a “step back and put the sunscreen conversation in context,” she said.
Mineral sunscreens have some cons, too. They “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. They are often harder to rub in, appear chalkier and feel more noticeable on the skin.
If you don’t like the way a particular sunscreen looks or feels, you’ll be less likely to use it consistently, Dr. Lester said. In her own practice, people with darker skin “often avoid mineral sunscreens because they tend to leave a white cast on the skin,” she said.
Testing by Wirecutter 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.
Does sunscreen harm coral reefs?
It can, Dr. Lester said.
Oxybenzone, octocrylene and octinoxate are among the primary sunscreen ingredients that can contribute to coral reef damage. The only two “reef safe” active ingredients approved by the F.D.A. are “non-nanotized” zinc oxide and titanium dioxide. (Non-nanotized means that the ingredient 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 ultraviolet protection factor (UPF) clothing (though you’ll still need to use sunscreen on exposed skin).
Do you need sunscreen if you have dark skin?
Yes. “It’s a misconception that darker-skinned people can’t get skin cancer,” Dr. Nambudiri said. Even though darker-skinned people may not burn as quickly as fairer-skinned people, they can still get sun damage that contributes to sunburns, aging, uneven skin tone and hyperpigmentation, Dr. Lester added.
Should I wear sunscreen every day?
Yes. “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 skin that isn’t exposed, it’s important to apply it to the face, ears, neck, hands, forearms and other often-exposed body parts to help prevent sun damage.
Can you be allergic to sunscreen?
Yes, said Dr. Whitney Bowe, a dermatologist in New York City. “Every summer, I have patients who come in with rashes, itchy skin or irritation, and they’re concerned they might be allergic to their sunscreen,” she said.
In these cases, allergies are possible. But these patients may also be having what dermatologists call irritant contact dermatitis, a nonallergic skin reaction to an ingredient in sunscreen that can cause mild redness, itchiness or stinging. This reaction tends to appear almost immediately after applying sunscreen and only on the skin where the sunscreen has been applied, said Dr. Hope Mitchell, a dermatologist in Ohio.
An allergy, on the other hand, “may take several days or even years of consistent use of the same product to develop,” Dr. Mitchell said, and it may spread to other body parts. Signs of an allergy may include swelling, extreme itching or a blistering rash.
Fragrances, preservatives, oils and botanical extracts are the most common sunscreen ingredients that cause either irritant contact dermatitis or an allergy, Dr. Bowe said.
Active ingredients in chemical sunscreens, such as oxybenzone, avobenzone and octocrylene, have caused skin reactions, though research suggests this is rare. And interactions between your sunscreen and “certain medications, topical creams or lotions may cause or exacerbate reactions,” Dr. Mitchell said.
Another possible reaction is photocontact dermatitis, which can occur when sunlight interacts with certain sunscreen ingredients. If you develop a rash on parts of the body that have been exposed to both sunscreen and the sun (such as your face), but not on parts that have been exposed only to sunscreen (such as under your chin), “photocontact dermatitis is possible,” Dr. Bowe said.
She suggested using fragrance- and essential oil-free formulations and sticking to mineral sunscreens, which have active ingredients that are less likely than those in chemical sunscreens to cause reactions. (Wirecutter’s guide to sunscreens includes several mineral-based and “sensitive” formulas that tend to contain fewer known irritants.)
If you think your skin is reacting to an ingredient in your sunscreen, stop using that formula, Dr. Mitchell said, but do not stop wearing sunscreen altogether. And if you’re concerned, consult a dermatologist, who can prescribe medication if needed.
If the problem persists after making these substitutions, Dr. Bowe and Dr. Mitchell both suggested patch allergy testing, which can help determine the specific ingredients that are causing the reactions.
