UV radiation vs. chemicals in sunscreen: Which is a bigger threat?

(CNN) — Even though summer is winding down in the Northern Hemisphere and school has started or is right around the corner, don’t put your sunscreen away just yet. You still need it to protect against skin cancer and premature aging.

Despite the clear benefits of sunscreen, questions about sunscreen safety — and even its necessity — have been debated for years. These doubts have been fueled in part by a growing number of social media influencers, as well as the 2021 discovery of the carcinogen benzene in a handful of since-recalled sunscreens. (The chemical, not an ingredient in sunscreen, appeared to be linked to the aerosol propellant.) Additionally, the US Food and Drug Administration moved to have manufacturers do more safety research on a dozen common sunscreen ingredients.

Sometimes it is hard to separate fact from fiction and figure out what is worth worrying about (or not).

The link between sun exposure and skin cancer is well established. Ultraviolet radiation is thought to cause up to 95% of basal and squamous cell carcinomas, and between 70-95% of melanomas in people with fair skin.

“Skin cancer is caused by exposing the cells in the skin to UV radiation, and particularly UVB radiation,” researcher Dr. Rachel Neale told CNN Medical Correspondent Meg Tirrell recently in a special episode of the podcast Chasing Life. Neale, a principal research fellow at the QMR Birkhoff, a medical research institute in Brisbane, Australia, has been studying skin cancer since 1993.

“Those most harmful rays cause skin cancer by causing mutations in the DNA in our cells,” Neale explained, noting that one mutation is not generally a big deal. “But what happens if that mutation occurs in a gene that’s really important for DNA repair, for example,” she said. “Then we get another mutation, and then we potentially get another mutation. And then eventually we tip our cells over into forming into a skin cancer.”

We’ve known since the 1990s that sunscreen helps lower the risk of developing skin cancer, especially the most deadly type, melanoma, and the less-lethal squamous cell carcinoma. (Basal cell carcinoma is by far the most common type of skin cancer; while it is rarely fatal, it can cause distress and be disfiguring.)

Chemicals in the crosshairs

But now there are questions about the safety of certain sunscreen ingredients.

There are two types of sunscreens: mineral (also called physical) and chemical. Mineral may be better than chemical (chemical hasn’t been studied enough is the problem) and both are better than skin cancer. But it’s truly a complicated answer.

“The physical blockers — so the titanium and zinc sunscreens — they sit on top of the skin basically and form a barrier,” Neale said. “Whereas the chemical sunscreens, they sort of bind to the top surface of the skin and turn the UV radiation into heat, (which) then disperse from the body’s heat.”

The FDA, which regulates sunscreen as a nonprescription drug, asked sunscreen makers in 2019 and again in 2021, to provide more safety data on 12 common ingredients so that they can have GRASE — Generally Regarded As Safe and Effective — status.

There are two reasons for the FDA’s request. First, because when the FDA began evaluating sunscreens in the 1970s, scientists didn’t fully appreciate how readily chemicals could be absorbed through the skin. Today, transdermal application is a common delivery system for certain medications, including nicotine, pain and hormone patches.

The second is the amount of sunscreen we are supposed to be applying, which increased from a few dabs here and there to a shot glass-full every two hours you are outside.

“If you use it as intended, which is what would make it effective, there’s a lot more of it that’s ending up in our bloodstream than we realized and the concern is that we don’t know enough about its safety,” researcher Laura Vandenberg told Tirrell on the podcast. Vandenberg is a professor of environmental health sciences at the University of Massachusetts Amherst, and researches endocrine disruptors.

“What the FDA has asked the manufacturers of…these products to do is to do studies where the sunscreen would be used as intended and then see how much of these chemicals end up in the bloodstream,” she said. “Because the FDA has standards for how much of these chemicals should be in our blood and currently they can’t meet that standard of both safe and effective.”

Vandenberg said she has concerns about some of these ingredients, including oxybenzone, which she researches in her lab. She said studies in cell cultures and research animals show that the chemical can mimic estrogen in the body, block the actions of androgens and alter thyroid hormone function — any of which could be problematic especially in vulnerable populations, for example a baby, a child going through puberty or someone who is pregnant and their fetus.

“Disruptions to hormones can lead to life altering changes, increased risk for disease,” she explained. “And those diseases might not show up for decades in a human.”

Vandenberg also said there’s increasing evidence from human populations.

“Some of the critiques of the FDA’s actions have come from scientists that are saying, ‘Well, we haven’t ever seen anything in human populations to suggest that these chemicals can cause harm.’ And that’s not really true,” she explained.

“When we measure how much of these chemicals are being released from the body — excreted from the body in urine — and then compare people and their risk of different conditions, there are studies that show that exposures to oxybenzone are associated with increased neurodevelopment problems in children and increased metabolic problems in children, and also increased risk of thyroid hormone issues,” she said.

But Vandenberg is careful to note that correlation is not causation. “Does that mean that we can say definitively that a chemical like oxybenzone causes those effects in people? No,” she said, “because we’re not purposefully exposing some people to oxybenzone and then comparing them to a group of people who weren’t exposed ever to oxybenzone (because) those people don’t exist.”

Vandenberg, who gives credit to the FDA for asking for more safety studies, stresses that just because certain sunscreen ingredients penetrate the skin doesn’t inherently make them unsafe.

“In this case, I think that really what they’re doing is signaling that there isn’t enough evidence to say that they’re dangerous,” she said. “But that’s not the standard that we should have for products that we’re putting all over our body, for products we’re putting on the bodies of children. We want to know that they’re safe, but we also want to know that they’re doing the job because the job of sunscreens is really critical.”

How the experts protect themselves

Vandenberg and Neale agree they both need to wear sunscreen, so what do they reach for?

“I use a chemical sunscreen every day,” Neale said. “I think it’s very tricky because the properties of the chemical sunscreens make them much more pleasant to use; the physical blockers tend to be a bit thicker, and they can form a bit of a white veil on the skin.” She also relies on covering up with clothing and avoiding the sun at its strongest.

Vandenberg has a different approach. “Based on what I know and in my own practice, I lean towards a physical sunscreen, and then use it correctly: more than you think you need, and reapplying every 90 minutes,” she said. She is quick to add that reaching for a chemical sunscreen is better than using nothing at all because “skin cancer is very real.”

Vandenberg notes that these chemicals are everywhere. “I study these chemicals. I am worried that we have allowed endocrine disruptors to be in sunscreen products, but they’re also in literally everything around us,” she said. “And removing that one product as a way to protect yourself from endocrine disruptors, and yet increasing your risk in this other area (skin cancer) is not a sound thing to do.”

“What we really need to do is demand safer products, and we can demand that from the companies that we give our dollars to,” she said. “We need to demand that of our regulatory agencies.”

For more of the conversation on sunscreens, listen to the full podcast here.

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CNN Audio’s Jennifer Lai contributed to this report.