Blog

A study of 17 commonly used synthetic “eternal chemicals” showed that these toxic substances can be easily absorbed through human skin.

New research published in Environment International demonstrates for the first time that a wide range of PFAS (perfluoroalkyl substances) – chemicals that do not degrade in nature – can penetrate the skin barrier and reach the body’s bloodstream.

PFAS are widely used in industries and consumer products from school uniforms to personal care products due to their water-repellent and anti-stain properties. While some substances are banned by government regulations, others are still widely used and their toxic effects have not yet been fully studied.

PFASs are already known to enter the body through other routes, such as inhalation or ingestion through food or drinking water, and are known to cause adverse health effects such as reduced immune response to vaccination, impaired liver function, and reduced birth weight.

PFASs are generally thought to be unable to breach the skin barrier, although recent studies have shown links between the use of personal care products and concentrations of PFASs in human blood and breast milk. The new study is the most comprehensive assessment to date of PFAS absorption into human skin and confirms that most of them can enter the body through this route.

The study’s lead author, Dr. Oddný Ragnarsdóttir, conducted the study while studying for her Ph.D. at the University of Birmingham. She explained: “The ability of these chemicals to be absorbed through the skin has previously been dismissed as the molecules are ionised. It is believed that the electrical charge that gives them the ability to repel water and stains also makes them unable to pass through the skin membrane.

“Our study shows that this theory is not always true, and that in fact absorption through the skin can be a significant source of exposure to these harmful chemicals.”

The researchers examined 17 different PFASs. The compounds selected were among the most widely used and most widely studied for their toxic effects and other ways in which humans may be exposed to them. Most importantly, they comply with chemicals regulated by the EU Drinking Water Directive.

In their experiments, the team used 3D equivalent models of human skin – multi-layered lab-grown tissues that mimic the properties of normal human skin, meaning the research could be conducted without the use of animals. They applied samples of each chemical to measure what proportions were absorbed, not absorbed or retained in the models.

Of the 17 PFASs tested, the team found that 15 substances showed significant dermal absorption—at least 5% of the exposure dose. At the exposure doses studied, absorption into the bloodstream of the most regulated PFAS (perfluorooctanoic acid; PFOA) was 13.5% with an additional 38% of the applied dose retained in the skin for potential longer-term uptake into the circulation.

The amount absorbed appears to correlate with the length of the carbon chain in the molecule. Substances with longer carbon chains show lower absorption rates, while compounds with shorter chains that have been introduced to replace longer carbon chain PFASs such as PFOA are more easily absorbed. The absorption of perfluoropentanoic acid, for example, is four times higher than PFOA at 59%.

Study co-author Dr Mohamed Abdallah said: “Our study provides the first insight into the importance of the dermal route as a route of exposure to a wide range of perennial chemicals. Given the large number of PFASs in existence, it is important that future studies seek to assess the risk of a wide range of these toxic chemicals rather than focusing on one chemical at a time.”

Study co-author Professor Stuart Harrad, from the University of Birmingham’s School of Geography, Earth and Environmental Sciences, added: “This study helps us to understand how important exposure to these chemicals through the skin may be and also which chemical structures may be most easily absorbed.

“This is important because we’re seeing a shift in the industry to chemicals with shorter chain lengths because they’re thought to be less toxic – but the trade-off could be that we’re absorbing more of them, so we need to know more about the risks involved.”