Fortune spoke with experts to understand the facts about sunscreen.

What is in sunscreen?

Depending on the product, you’ll find several active ingredients that provide broad spectrum protection against the sun’s damaging UVA and UVB rays, according to the American Academy of Dermatology. 

Basically, there are two varieties of sunscreen: physical and chemical. Physical, also known as mineral-based, contains two main active ingredients, zinc oxide and titanium dioxide, which act as a physical barrier between your skin and the sun. Sunscreens without these two active ingredients are classified as chemical, and usually contain a mix of other active ingredients.

What are the concerns about sunscreen?

Most of the concerns swirling about sunscreen involve the active ingredients in chemical sunscreens.

A 2020 randomized clinical trial of the U.S. Food and Drug Administration (FDA) found that six active ingredients (avobenzone, oxybenzone, octocrylene, homosalate, octisalate, and octinoxate) in various chemical sunscreens were systemically absorbed into the body.

“The concern isn’t about them being chemical sunscreens per se, but about the fact that they are absorbed through the skin,” FDA press officer Cherie Duvall-Jones tells Fortune. “This means we need to know what these absorbed sunscreen ingredients do when they get in the human body. For example, can they lead to cancer or cause developmental or reproductive problems if people use sunscreens every day?”

That’s a question Emily Spilman, a safety scientist with the nonprofit Environmental Working Group (EWG), would like to see better answered. Based on her research into chemical ingredients in sunscreen, she’d like to see stricter regulations from the FDA.

“Some [active ingredients] are linked to skin allergies and immunotoxicity,” Spilman tells Fortune. “Some of them are also linked to more concerning impacts like hormone disruption, endocrine disruption.”

Spilman pointed out that two ingredients in particular, octinoxate and oxybenzone, have been linked to disruption of the endocrine system, which creates and releases hormones for myriad bodily functions.

Understanding hormone disruptors and carcinogens

Experts are increasingly warning against the health effects of hormone or endocrine disruptors. According to the National Institute of Environmental Health Sciences, endocrine disruptors are “natural or man-made chemicals that may mimic or interfere with the body’s hormones” and are associated with various health problems, including some cancers.

“Four studies published in 2020 support previous findings that oxybenzone can act as an endocrine disruptor and may increase the risk of breast cancer and endometriosis,” an EWG spokesperson tells Fortune. And while it’s not definitive that hormone disruptors will directly cause cancer, he says, “some common contaminants in sunscreens are also linked to carcinogenicity.” Carcinogens are substances either known to cause cancer or that may be linked to cancer.

Some of those ingredients to look out for—in addition to octinoxate and oxybenzone—are octocrylene, which the EWG says is often contaminated with benzophenone, a known carcinogen. Aerosol sunscreens have also been found to be contaminated with benzene, another cancer-causing chemical, the EWG says.

In 2019, the FDA requested data from the manufacturers of these chemicals to determine their safety. 

“To date, none of the manufacturers of sunscreen active ingredients currently on the U.S. market have provided these data to the FDA,” Dr. Theresa Michele, Director of the FDA’s Office of Nonprescription Drugs, tells Fortune. 

“Although the FDA does not have information indicating that currently marketed sunscreen active ingredients … have established safety risks, it’s important to determine whether or not there are risks with use of these ingredients,” Michele says. “This is why the agency has asked for the missing information on safety.”

Which sunscreen is safest to use?

“Trying to avoid endocrine-disrupting chemicals can be difficult as a consumer,” Spilman says. But it’s not impossible.

The safest bet is to use broad spectrum mineral-based sunscreen, Spilman says. You’ll know it’s mineral sunscreen if the only two active ingredients are zinc oxide and titanium dioxide, she notes.

Additionally, Spilman advises using a stick mineral sunscreen or one that’s cream-based, because aerosol (spray) sunscreens can pose yet another health threat if inhaled.

“Because of the potential of exposure through inhalation, the International Agency for Research on Cancer has classified titanium dioxide as possibly causing cancer in humans,” EWG tells Fortune. “For this reason, powdered or spray formulations containing titanium dioxide are a concern.”

Spilman also recommends avoiding sunscreens that included “fragrances” on their inactive ingredients label. “That term can really hide the mixture of potentially harmful chemicals behind it,” she says. Those can often include phthalates, which are also endocrine-disrupting chemicals.

Sunscreens made for young children, she adds, are a better option that anyone can use, as they are usually formulated with higher safety standards—but those may also contain hidden phthalates, according to recent research. When choosing a children’s sunscreen, it’s better to opt for fragrance-free, and those that don’t come in plastic when possible.

In addition to following EWG’s sunscreen guidelines, you can follow the general advice of the American Academy of Dermatology by looking for products with:

• Broad-spectrum protection (protecting against both UVA and UVB rays)
• SPF 30 or higher
• Water resistance

The academy also recommends reapplying sunscreen every two hours when outside, or after swimming or sweating. And remember that you need sunscreen even on cloudy days, as up to 80% of the sun’s UV rays can penetrate the clouds.

Bottom line: You should still wear sunscreen

Despite some concerns about what’s in our sunscreen, the American Academy of Dermatology emphasizes the importance of wearing it.

“Skin cancer is the most common cancer in the U.S., and unprotected exposure to the sun’s harmful ultraviolet rays is a major risk factor for skin cancer,” the AAD stresses in its official sunscreen guidelines.

In a statement to Fortune, the AAD added: “While recent studies have shown that some chemical sunscreen ingredients can be absorbed into the body through the skin, the data does not show that there are any effects on a person’s health. Those with concerns about chemical sunscreen ingredients can opt for a physical sunscreen.”

The FDA, EWG, and AAD all encourage people to wear sunscreen outside. While there’s no clear evidence that sunscreen products cause cancer, the evidence connecting UV rays to cancer is clear.

For more on skincare:

• Children’s skin care products could contain a hidden danger, study finds
• 8 toxic ingredients lurking in your skincare and hair products. What to avoid
• Skin cancer affects about 6 million Americans each year. Here’s when—and how often—you should consider getting checked