Why sunscreen ingredients need more safety data

Sunscreen is an important way to protect people from skin cancer and other harmful effects of ultraviolet (UV) rays. But some chemicals or filters in sunscreens do have come under scrutiny recently for their potential impact on the environment and human health. Most of the concerns center on ingredients in chemical sunscreens—such as oxybenzone, avobenzone, octocrylene, homosalate, octisalate, and octinoxate—that absorb ultraviolet (UV) rays.

Physical or mineral sunscreens – which include only zinc oxide and titanium dioxide as active ingredients – are less dangerous to human health safety because they block UV rays by sitting on the skin and deflecting them.

There are also concerns that oxybenzone and other sunscreen chemicals can cause coral bleaching and damage to aquatic life when they wash and enter the water.

A report published Aug. 9 by the National Academies of Sciences, Engineering, and Medicine concludes that while people should continue to use sunscreen—and indeed use more of it more often—further research is needed on several aspects of the safety of its active ingredients .

Here’s what the report says about sunscreen products and what it means for human health and the environment.

Sunscreen is underused

Only about a third of people in the U.S. use sunscreen regularly, the report found, even though about 70 to 80 percent of Americans use it when they’re at the beach. However, most sunscreen users don’t apply enough—the American Academy of Dermatology advises using one ounce for full body coverage—and often don’t reapply every two hours as recommended. In addition, white Americans use sunscreen more often than people of color, who tend to have lower rates of skin cancer than white people, but are they are more likely to die from the disease.

Read more: The safest sunscreens to buy—and which ingredients to avoid

The best available evidence – obtained through large randomized controlled trials and longitudinal observational studies – shows that broad-spectrum sunscreens (meaning they protect against both UVA and UVB rays) with an SPF higher than 30 reduce the risk of cancer of the skin, sunburn and aging caused by sun exposure. However, sunscreen should be used in combination with other precautions, such as wearing hats, avoiding sun exposure during the hottest parts of the day, and seeking shade.

There is not enough research on safety

Scientists have found no toxic effects in humans that would outweigh the benefits of using sunscreen. But the report’s authors say more safety studies are needed, as US Food and Drug Administration (FDA) studies published in 2019 and 2020 found evidence that many chemical filters in sunscreen penetrate the skin and can stay there for days. While this does not necessarily mean that the chemicals are dangerous, some have been found in the body at concentrations higher than the upper thresholds set by the FDA above which safety studies must be conducted. Homosalate and oxybenzone, which absorb ultraviolet light, were above this level three weeks after application in one study. Some animal studies have also raised concerns about UV filters, including changes in hormones and gene expression. The report’s authors also point to several gaps in human safety research; for example, the safety studies didn’t follow people for long periods of time, meaning they couldn’t look at potential outcomes that might emerge over time, such as cardiometabolic risk, cancer risk, or fertility problems.

Overall, however, the weight of scientific evidence is firmly on the side of using sunscreen, the authors conclude. Scientific reviews that have examined various studies looking at the use of UV filters have found encouraging signs that the filters are safe for humans. The reviews did not conclude that concentrated levels of UV filters harm male or female fertility, female reproductive hormone levels, fetal growth, or children’s neurological development. “To date, no levels of toxic effects in humans have been found that exceed the benefits of these filters in reducing overexposure to [ultraviolet rays]”, the authors write. “However, all authors acknowledge significant gaps in the data.”

Effects on other species also deserve more study

While scientists have studied how sunscreen chemicals affect certain plant and animal species, data is lacking for many other important species, including corals, the authors say. They argue that there needs to be more testing of the toxicity levels of sunscreen ingredients in different marine life, especially in places that may be more vulnerable to exposure. These include coral reefs in shallow areas near places where people do many recreational activities, such as swimming; in slow-moving freshwater environments where there is also plenty of entertainment; or in locations exposed to sewage.

How sunscreen works in the real world

The report’s authors say scientists need to learn more about the effects of sunscreen chemicals on the real-world environment. For example, while some UV filters (including avobenzone, dioxybenzone, and octocrylene) have been shown to take a long time to biodegrade when tested in laboratories, researchers need to test how they accumulate in nature, such as by sampling organisms and soil , the authors write.

Another priority should be testing how natural stressors such as climate change and pollution interact with sunscreen chemicals that enter the environment. The scientists say more research is needed on what happens when ecosystems are subjected to multiple types of stress at the same time, as well as what happens when UV-filtering chemicals combine with other threats, such as rising temperatures and pollutants.

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