5 Things We Now Know About the Safety and Effectiveness of Sunscreen

There’s no debate about it: Exposure to sunlight has been directly linked to skin cancer.

According to the Skin Cancer Foundation, one in five Americans will develop skin cancer over the course of their lifetime. And studies have shown that 90% of non-melanoma skin cancers (like squamous-cell and basal-cell carcinoma) and 86% of melanoma cases (the deadliest form of the disease) are derived from exposure to UV radiation from the sun.

Yes, those are pretty high numbers. But you can take some comfort in knowing that you can reduce your risk of developing skin cancer by wearing sunscreen.“There’s a cumulative body of evidence collected over the past decade that shows the positive effects of wearing sunscreen,” says Elizabeth Tanzi, M.D., Clinical Associate Professor of Dermatology at George Washington University. “It works by either deflecting UV rays completely, or by absorbing them, so they can’t get into your DNA and cause cancer and accelerated skin aging.”

Case in point: One large-scale study published in the Journal of Clinical Oncology tracked over 1,600 individuals over 15 years. Half of the participants were asked to put on sunscreen daily; the other half were told to follow their usual sunscreen habits, which ranged from habitual wear to none at all.

At the end of the study, researchers found that twice as many people in the group that wasn’t as vigilant about sunscreen usage developed melanomas, compared to those who applied sunscreen every day.

In order for sunscreen to really do its job, you need to use it properly. This means applying it at least 15 minutes before heading outdoors so it can fully set on the skin’s surface and provide maximum resistance against the elements, including water.

There’s also a formula to how much you should apply. The rule of thumb is to use 1 ounce, which is about the size of a golf ball, for your whole body. Bottom line: Aim to cover all exposed skin with an even layer of sunscreen.

Water-resistant sunscreen is typically good for 40 or 80 minutes (check the label on your bottle to be sure), but to play it safe, reapply your sunscreen after swimming, advises Joshua D. Williams, Principal Scientist, Johnson & Johnson Consumer, Inc.

“There’s no such thing as a completely towel-proof sunscreen, so as you dry off, you’re most likely removing what’s on your skin,” he explains.

If you’re not planning to hit the water, reapply your sunscreen at least every two hours, but keep in mind that this doesn’t mean you can sit in direct sunlight for several hours straight without harming your skin.“You still have to use smart sun behavior,” Williams says. “So be mindful of your exposure time, seek shade and wear hats and protective clothing.”

In fact, a recent Johnson & Johnson study published in JAMA Dermatology found that while SPF 100 is more effective for sun protection than simply sitting under a beach umbrella, neither on their own can completely prevent sunburns outside of stringently controlled laboratory conditions. So you should consider wearing sunscreen even in the shade.

There are two types of sunscreen: mineral and chemical. The latter contains such ingredients as avobenzone and oxybenzone, which work by absorbing damage-causing UV rays. Mineral sunscreens, which are composed of zinc oxide and titanium dioxide, sit atop the skin’s surface and work by absorbing, deflecting and scattering the dangerous rays.

Both formulations are considered safe and effective, Dr. Tanzi says.

Much of the confusion about chemical sunscreens comes from the fact that some studies have suggested that ingredients like oxybenzone could disrupt hormone levels, while others have concluded that they have no such effect on the endocrine system.

“We’ve been using some of these ingredients for 30 years with a proven safety record—and there’s much more evidence of benefit than harm,” Williams says."If these ingredients are getting into our systems through sunscreen, the amount is so small, it’s negligible,” Dr. Tanzi adds.

In fact, in a review published in the journal Photodermatology, Photoimmunology & Photomedicine, researchers carefully examined all of the existing studies surrounding sunscreen ingredients—including oxybenzone and retinyl palmate—and concluded that studies done on humans did not show toxicity from any of them.

The American Academy of Pediatrics recommends that children over the age of 6 months avoid the sun during peak hours (typically between 10 AM and 4 PM), and wear sun-protective clothing and sunscreen with an SPF 15 or greater on exposed skin. Infants under 6 months should avoid the sun altogether.

Yet scroll through mommy groups on social media and you’ll probably find posts questioning the safety of sunscreen use on young children.

The truth? Studies have shown it’s crucial for kids to wear sunscreen. In fact, the Centers for Disease Control and Prevention (CDC) recommend it.

“Research continues to emerge that sunburns, particularly bad ones, in youth lead to poor skin health outcomes—like skin cancer and premature skin aging—later in life,” Williams notes. “Using sunscreen is certainly safer for your skin than getting a sunburn.”

Many dermatologists do suggest that children wear mineral sunscreens over chemical versions, but not because the chemicals are dangerous.

“Kids tend to have more sensitive skin than adults, so for that reason, I recommend physical [a.k.a. mineral] sunscreens with zinc and titanium dioxide, which tend to cause less irritation,” Dr. Tanzi explains.

The SPF on a sunscreen label refers to its “sun protection factor.” And the higher the number, the better the protection level.

So how high should you go?

In a recent study published in JAMA Dermatology, 97% of dermatologists surveyed said they recommended SPF 50, and over 80% believe higher SPFs offer a considerable additional margin of safety.

“It’s about how much light gets through the product that causes skin damage over time,” Williams explains, referring to the fact that SPF 50 lets through 2% of light, while SPF 100 lets through just 1%. “By using the higher level, you cut the amount of light in half and double the efficacy,” he adds.

Another factor to consider: Experts say it’s unlikely you’re getting the exact SPF level that’s printed on the bottle—but not for the reason you may think.When people are having fun outdoors, they don’t necessarily use sunscreen as it’s indicated. “People don’t reapply enough, they apply it unevenly or they don’t realize they’re inadvertently removing it,” Williams explains. “All of these aspects lead to getting less protection than demonstrated in the lab.”

So starting with a higher number gives you a better chance of getting an effective level of SPF, avoiding bad tan lines—and helping keep cancer at bay.