Why You Really Shouldn’t Make Your Own Sunscreen

This summer, some influencers have jumped on the bandwagon of posting TikToks of themselves making sunscreen at home after a popular influencer did so. Experts are now warning people not to make DIY sunscreen as it can be dangerous.

Influencer Nara Smith, 22, who is known for sharing videos of herself making everything from cereal to cough drops from scratch, posted a TikTok in June of her husband, Lucky Blue Smith, mixing together coconut, beeswax, shea butter, cocoa butter, jojoba oil, and zinc oxide powder to create sunscreen (the latter is a main ingredient in many mineral-based sunscreens). Since then, her video has received about 2 million likes. And others—like TikToker Avery Cyrus, 24, who has 9.3 million followers—have also shared videos of themselves making their own sunscreen.

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But some dermatologists have expressed concern over DIY sunscreen, making their own social media posts and cautioning people not to do so.

“The dangers related to homemade sunscreen is, bottom line, it’s not going to protect your skin how it should,” says Dr. Aamna Adel, a dermatologist based in London. “Just because it contains zinc oxide … does not mean that it’s going to be protecting you against UV rays.” People who make their own sunscreen will “be increasing their risk of sunburn [and] developing skin cancer.” (Adel has done some paid campaigns for brands that have sunscreen products in the past.)

A representative for Smith declined TIME’s request for comment, and a representative for Cyrus did not respond.

The U.S. Food and Drug Administration (FDA) regulates sunscreens as nonprescription drugs. Products on the market “have to undergo extensive testing,” says Dr. Brooke Jeffy, a dermatologist based in Scottsdale, Ariz. Dermatologists say there are a few reasons why making sunscreen yourself can be dangerous. First, the process of making sunscreen is quite complicated—the formulas are precise and can be difficult to replicate at home. And second, there’s no way to know how much protection a homemade sunscreen will offer you. Because of that, your sunscreen may have inconsistent or ineffective coverage, which could increase your risk of skin cancer and lead to premature signs of aging, like wrinkles and sun spots.

“Let’s say you use 15% zinc, but you’re adding other things into it. So do you really have that same percentage in your final product? How do you really know that you have what you think you have?” says Dr. Doris Day, a dermatologist based in New York City.

“It’s not that easy to make a mineral-based sunscreen and have it spread easily and smoothly,” Day says.

Some dermatologists say that even if Smith’s video wasn’t meant to be taken seriously, they worried that people may try the recipe themselves

Concerns about the potential health risks associated with the ingredients in chemical sunscreens have bubbled up over the past few years. The DIY videos area reaction to that, says Jeffy: “I think it’s sort of based on a couple of misconceptions that are out there that sunscreens are harmful, and that you are safer to be making products yourself.” But the FDA, the U.S. Centers for Disease Control and Prevention, and medical associations all recommend using sunscreen because it can help prevent skin cancer. Jeffy suggests that anyone worried about chemical-based products use mineral sunscreens instead.

Kate Ring, a 43-year-old TikTok influencer who lives in Kent, U.K., has also posted videos of her homemade sunscreen recipe, which she’s been using for yearsbecause she was concerned about the ingredients in sunscreens on the market. She says she’s not phased by warnings from doctors and public-health officials, arguing that the process to make sunscreen is “not complex at all.”

“I am by no means an expert,” Ring says. “Obviously, I didn’t go put it on and then go and bake out in the sun for eight hours. I tested it over weeks actually, and over time periods to make sure that I was getting it right.”

But Jeffy questions how effective at-home “testing” like that actually is. And experts say that not visibly burning is not an indication of being adequately protected from the sun.

Day says that if someone doesn’t want to listen to dermatologists, that’s their decision—but that, “unfortunately,” some people may listen to those influencers over experts.

“My interest is protecting people from misinformation and products that can be damaging to their skin,” Day says. “All I can do is give information and hope that it makes sense.”