Some studies raise concerns about sunscreen chemicals. But if you dig deeper, evidence is still lacking, experts say.


It is part of a daily routine for some, and for others, a routine source of doubt and uncertainty: to wear sunscreen or not?

Recent research has deepened the confusion. In a clinical trial published this year, researchers from the Food and Drug Administration reported that six common chemical ingredients in sunscreens permeate the skin and enter the bloodstream in amounts high enough to require extra safety testing by the FDA. Levels of the chemicals, which included oxybenzone and avobenzone, increased with each subsequent day of use.

It can feel like a lose-lose scenario: If you put sunscreen on, you risk damage from chemical ingredients. If you don’t, you risk UV damage from the sun.

Experts say there is still no evidence that chemical sunscreens cause harm, especially if used on limited areas that are most exposed to the sun. There are other ways of protecting yourself from UV rays in addition to sunscreen. And other sunscreen options exist: Studies show that mineral alternatives, including zinc dioxide and titanium dioxide, are both safe and effective.

“There’s really no reason to forgo sunscreen when we have known tested safe alternatives,” says Kanade Shinkai, a dermatologist at the University of California at San Francisco. Despite what can seem like alarming research, she adds, chemical versions are not necessarily dangerous. “The systemic absorption of chemical sunscreen does not necessarily mean that it’s unsafe or unhealthy. And avoiding the risks of UV exposure is still a very important health aim.”

Sunscreen has a decades-long history that gave it a pass onto pharmacy shelves, Shinkai says. Invented before the FDA developed standards for testing over-the-counter products for safety and effectiveness, sunscreen was grandfathered in for sale before its ingredients had been thoroughly studied.

Over time, plenty of evidence has accumulated to show that UV radiation from the sun triggers skin cancers, including melanoma, and that sunscreen helps mitigate those risks.

In one long-running study of more than 1,600 people that began in 1992, Australian researchers randomized people to either wear sunscreen or do what they normally do. After more than a decade of follow-up, results showed that, compared with the group that didn’t get instructions to slather it on, the sunscreen group developed far fewer cases of skin cancer, says Henry Lim, a dermatologist at the Henry Ford Medical Center in Detroit.

In another study published in 2012, one of the same researchers and colleagues estimated that increasing sunscreen use could lead to between 231,000 and 797,000 fewer melanomas for people with white skin in the United States by 2031.

But for decades, evidence has also been accumulating to suggest that the ingredients in sunscreen can get through our skin and into our bodies.

In a 1997 study, researchers instructed nine healthy people to apply sunscreen with a sun protection factor of at least 15 on their forearms, using the amount they would normally use. Twelve hours later, they washed the sunscreen off with soap and water. Urine samples taken before and after application showed that between 1 and 2 percent of the applied amount of oxybenzone seeped through the skin.

Then in 2008, researchers from the Centers for Disease Control and Prevention analyzed more than 2,500 urine samples collected as part of the long-running National Health and Nutrition Examination Survey. They found the sunscreen ingredient benzophenone-3 in nearly 97 percent of samples. The study couldn’t show that sunscreen was the source of the chemical in people’s bodies, Shinkai says: The same chemicals are also used on commercial products, such as outdoor lawn furniture. Still, the results were suggestive.

Testing data from the FDA finally started to come out in 2019, two decades after the agency announced its plans to systematically investigate the safety of sunscreen. The study included 24 people who applied sunscreen four times a day for four days, covering 75 percent of their bodies with each application. Participants were randomized into four groups, who received different combinations of four active ingredients (avobenzone, oxybenzone, octocrylene, and ecamsule) in creams, lotions or sprays.

Results drew plenty of attention: analyses of blood plasma showed, for the first time, concentrations of all four ingredients that exceeded levels at which FDA guidelines require more safety testing.

“It was the first study to really demonstrate that four really common ingredients that are found in the top-selling sunscreens are all absorbed into the bloodstream, and they do so at levels exceeding that safety threshold set by the FDA,” Shinkai says.

The FDA’s follow-up study in 2020 duplicated the results for three of the same ingredients and three others in 48 people. It also found levels exceeding the threshold after a single application.

Shinkai emphasized that the studies don’t show that sunscreen causes harm, and that more research is needed. “We have no idea whether there is actually any negative health impact,” she says. “We need the data.”

One reason not to freak out yet about the new findings is that the amount of sunscreen that participants were instructed to use does not mimic real-world conditions, Lim says.

Multiple studies suggest that, when left to their own whims, people use 80 percent less sunscreen than the 2 milligrams per centimeter of skin enforced in the study. Study participants also covered most of their bodies with sunscreen multiple times a day, whereas typical use is far less extensive.

“Most of us only do that for the three days a year we go to Florida,” Shinkai says.

Even if sunscreen chemicals do get into the bloodstream, it is not clear that they cause harm there, either.

Animal studies have raised concerns about endocrine disruption and reproductive issues. But animals are not people, Lim says. And despite decades of sunscreen use, there has been no population-wide signal that rates of infertility, birth defects or other health problems are higher in people who use more sunscreen or in places where people apply more of it.

So far, safety research has included only healthy adults, leaving a dearth of information about potential risks to pregnant women and children. Because children’s bodies have a relatively larger surface area compared with adults, absorption is theoretically higher, Kanade says. Lim advises his pregnant patients to use mineral sunscreens, which have been studied extensively.

To stay safe from the sun, researchers also recommend looking beyond sunscreen to other strategies. Wear hats, sunglasses and clothing. Concentrate time outdoors during the hours of the day when the sun is not as intense — early in the morning or later in the afternoon. Sit in the shade. And take a vitamin D supplement to avoid inconsistent evidence about how much of the vitamin people manage to get from sun exposure.

“What I tell all my patients is that we do know that excessive sun exposure is not good for your skin, from wrinkling to skin cancer,” Lim says.

Protecting yourself requires a multipronged approach, he adds., 17 May 2020