Synthetic "forever chemicals" can be absorbed through human skin

A new study confirms that synthetic ‘forever chemicals’ can permeate human skin and reach the body’s bloodstream.

synthetic ‘forever chemicals’ absorbed through human skin
PFAS are toxic manmade chemicals that don't degrade in the environment. Photo: Adobe

Perfluoroalkyl substances, or PFAS, are manmade chemicals which don’t break down in nature. They can enter the body through inhalation or ingestion via food or drinking water and have several adverse health effects, such as a lowered immune response to vaccination and impaired liver function.

It was thought PFAS couldn’t breach the skin barrier. However, new research has shown, for the first time, that 17 of these commonly used toxic chemicals can be readily absorbed through the human skin and make their way into the bloodstream.

Useful but toxic

PFAS are used in a wide range of industrial and consumer products – from waterproof clothing and school uniforms, to personal care products – because of their water and stain repellent properties. Although government regulation has banned some of the chemicals, others are still widely used, and their toxic effects have not yet been fully investigated.

Recent studies demonstrated a link between personal care products and PFAS concentrations in human blood and breast milk, but this new study is the most comprehensive yet to analyse the absorption of PFAS into human skin. It confirms that most of them can penetrate the skin.

“The ability of these chemicals to be absorbed through skin has previously been dismissed because the molecules are ionised,” explains Dr Oddný Ragnarsdóttir, who conducted the research for her PhD at the University of Birmingham. “The electrical charge that gives them the ability to repel water and stains was thought to also make them incapable of crossing the skin membrane. Our research shows that this theory does not always hold true and that, in fact, uptake through the skin could be a significant source of exposure to these harmful chemicals.”

“Our study provides first insight into significance of the dermal route as pathway of exposure to a wide range of forever chemicals,” says Dr Mohamed Abdallah, study co-author. “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.”

Dermal absorption

The researchers investigated 17 widely used and widely studied PFAS regulated by the EU’s Drinking Water Directive. The team used multilayered laboratory grown tissues to mimic the properties of normal human skin and applied samples of each chemical to measure what proportions were absorbed, unabsorbed, or retained within the models.

Fifteen substances showed substantial dermal absorption – at least 5% of the exposure dose. At the exposure doses examined, absorption into the bloodstream of the most regulated PFAS, perfluoro octanoic acid or PFOA, was 13.5% with a further 38% of the applied dose retained within the skin for potential longer-term uptake into the circulation.

synthetic ‘forever chemicals’ absorbed through human skin
PFAS in personal care products may be absorbed through the skin. Photo: Nataliya Melnychuk on Unsplash

The amount absorbed appeared to correlate with the length of the carbon chain within the molecule. Those with longer carbon chains had a lower level of absorption, while compounds with shorter chains introduced to replace longer carbon chain PFAS like PFOA, were more easily absorbed, for example, absorption of perfluoro pentanoic acid was four times that of PFOA at 59%.

“This study helps us to understand how important exposure to these chemicals via the skin might be and also which chemical structures might be most easily absorbed,” adds Professor Stuart Harrad, from the School of Geography, Earth and Environmental Sciences. “This is important because we see a shift in industry towards 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.”

News Reference

Ragnarsdóttir, O. Abdallah, M. and Harrad, S. (2024) Dermal bioavailability of perfluoroalkyl substances using in vitro 3D human skin equivalent models, Environment International.