In early April, the Environmental Protection Agency set its first-ever limit on these “forever chemicals” in drinking water, following mounting evidence that chemicals in contaminated water can pose a health risk to people at even the smallest detectable levels of exposure. Per- and polyfluoroalkyl substances, or PFAS, are a man-made class of thousands of carbon-fluorine bonded compounds developed to make products and coatings that repel grease, water, oil and heat. Known as “forever chemicals,” PFAS can persist in the environment for centuries.

It is known that PFAS can enter the body through contaminated food and water as well as by inhaling polluted air. But it was previously thought that PFAS were unable to breach the skin barrier. This study adds to the limited body of evidence that proves dermal exposure to PFAS can lead to skin absorption.

Waterproof cosmetics like mascara, long-wear matte lipsticks and waterproof clothing are examples of products with PFAS that could be absorbed through the skin, said Graham Peaslee, a physics professor at the University of Notre Dame who frequently tests for PFAS in everyday products. Peaslee was not involved in the study. The chemicals are found in hundreds of household, personal care and beauty products — including cosmetics, water-repellent clothing, hand sanitizers and other products that make direct contact with human skin. PFAS in general have been linked to several kinds of cancer, infertility, high cholesterol, low birth weights, and negative effects on the liver, thyroid and immune system.

The new study extends the results of a single human subject study that mixed PFOA with sunscreen and applied it to the skin, concluding that PFAS could be taken up by the skin. Using cultured human skin models — which mimic real skin — researchers examined the absorption potential of 17 commonly used synthetic “forever chemicals.” Researchers then assessed the amount that crosses the skin barrier into bloodstream, the totals only absorbed into the skin and totals that don’t get absorbed at all.

The results found shorter carbon chained compounds had higher absorption percentages into that bloodstream than longer chained compounds. Harrad, an environmental chemistry professor at the University of Birmingham, explained that it’s easier for smaller chemicals to penetrate the skin barrier, then accumulating in blood.

“It suggests that the lower molecular weight [PFAS] which had been introduced as substitutes for PFOA, for example, that they are more easily absorbed through the skin.”

Perfluoro-n-pentanoic acid (PFPeA), a five-carbon chain compound, had nearly 60 percent absorption from the skin to the blood. While perfluorobutane sulfonate (PFBS), a four-carbon chained compound, had nearly 50 percent absorption to the bloodstream.

Yet other compounds with nine carbons like perfluorononane sulfonate (PFNS) didn’t penetrate to the bloodstream at all.

But researchers predict longer chain carbons could still eventually enter the bloodstream with more time after it is absorbed through skin. In the 36 hours that the study monitored, only about 14 percent of perfluorooctanoic acid (PFOA), which has eight carbons, was absorbed into the bloodstream but over 38 percent was absorbed into the skin. Nearly 70 percent of PFNS was absorbed into the skin although none entered the blood.

“We think it’s unlikely it’s going to go back the other way: It’s not going to be coming out of your skin. It’s more likely to be transferring through,” Harrad said. The amount transferred through the skin depends on the amount of product used, the concentration of PFAS and the type of PFAS in the product.

Cosmetic products with PFAS that are directly applied to the skin may penetrate the skin faster than fabrics and clothing with PFAS because, in the latter products, the PFAS would first need to be released from the product material before it could be absorbed into the skin through sweat or oils, Harrad said.

“We are continuously surrounded by consumer products that intentionally or unintentionally have things that we probably shouldn’t be using,” Peaslee said. Absorption could be heightened in thin skin areas like the neck, groin and underarm areas, he said.

But Peaslee — who says the primary source of PFAS exposure is through drinking water — is unsure about what fraction of exposures may come through skin contact.

“We are coating ourselves in this stuff every day, so the long-term prognosis is that a lot of this stuff can go through the skin and at surprising rates,” Peaslee said.

Katie Pelch, an environmental health scientist at the Natural Resources Defense Council, an advocacy group, said the study raises concerns about routine showers and baths in contaminated water as well as swimming in water with high levels of PFAS.

The study examines the same suit of chemicals associated with immune, hormonal and developmental effects, as well as varying cancers. Pelch says the type of exposure doesn’t change the potential health risks once PFAS enter the body.

“These chemicals aren’t metabolized by your body, so they’re not changed if they come in through in our mouth, in our digestive system, or if they come into our blood,” Pelch said.

There are only eight states that have acted to restrict PFAS in personal care products. Five chemicals covered in the EPA’s new drinking water standard were examined in the study.

Harrad says the next step in research is to expose cultured human skin models to different consumer products that contain PFAS and monitor absorption. For consumers, he suggests avoiding cosmetic products that contain PFAS and seeking out PFAS free items.

He said people need to “push for awareness about what actually is being used in products and be an actively aware consumer of these things.”