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[Image above] PFAS chemicals, which are used as ingredients in some cosmetic products, are now confirmed to enter the human body through skin—demonstrating the risk of exposure to these harmful chemicals. Credit: Ron Lach, Pexels


The U.S. Environmental Protection Agency’s ability to regulate pollution has experienced some significant curtailments in the past two years because of several U.S. Supreme Court rulings. Despite these setbacks, the federal agency did successfully issue the first legally enforceable national drinking water standards for five common types of per- and polyfluoroalkyl substances (PFAS) in April 2024.

Credit: PBS NewsHour, YouTube

PFAS are a large group of synthetic chemicals containing linked chains of carbon and fluorine. The strength of the carbon–fluorine bond makes it extremely unlikely that these chemicals will degrade naturally in the environment, hence their nickname “forever chemicals.”

Since the first PFAS were invented in the late 1930s, researchers have identified a growing number of negative environmental and health effects of these chemicals, including reduced immune system functioning and increased risk for some cancers. Yet regulations to restrict the use of PFAS or mandate its cleanup are slow to materialize.

The new drinking water standards are limited, but they are expected to protect some 100 million people from exposure and prevent tens of thousands of serious illnesses. The number of people who benefit from this regulation may be even larger, however, based on new findings by researchers at the University of Birmingham. For the first time, they proved indisputably that a wide range of PFAS can permeate the skin barrier and reach the body’s bloodstream.

As explained in the university press release, PFAS are believed to enter the body mainly through ingestion via food or drinking water or by being breathed in. Entry through the skin was considered impossible because PFAS molecules are ionized (electrically charged), which supposedly would prevent the molecules from crossing the skin membrane. However, recent studies, such as here and here, showed links between the use of personal care products and PFAS concentrations in human blood and breast milk.

The new study out of Birmingham aimed to confirm this link as causation rather than just correlation. To do so, they conducted in vitro tests on human skin equivalent models, which are multilayered laboratory grown tissues that mimic the properties of normal human skin.

Of the 17 different PFAS tested, 15 substances showed substantial dermal absorption (at least 5% of the exposure dose). The amount of PFAS absorbed appeared to correlate with the length of the carbon chain within the molecule. Longer carbon chains equated to lower levels of absorption, while compounds with shorter chains were more easily absorbed.

In the press release, first author and Ph.D. student Oddný Ragnarsdóttir explains their findings dispel the belief that ionization prevents permeation and that, in fact, “uptake through the skin could be a significant source of exposure to these harmful chemicals.”

In addition, the finding that shorter carbon chains are more easily absorbed is worrisome considering the recent trend in manufacturing, according to senior author and professor of environmental chemistry Stuart Harrad.

“…we see a shift in industry toward chemicals with shorter chain lengths because these are believed to be less toxic—however, the trade-off might be that we absorb more of them, so we need to know more about the risks involved,” he says in the press release.

Ultimately, given the large number of existing PFAS, “it is important that future studies aim to assess the risk of broad ranges of these toxic chemicals, rather than focusing on one chemical at a time,” says Mohamed Abdallah, coauthor and associate professor of persistent organic pollutants and emerging contaminants, in the press release.

The open-access paper, published in Environment International, is “Dermal bioavailability of perfluoroalkyl substances using in vitro 3D human skin equivalent models” (DOI: 10.1016/j.envint.2024.108772).

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