A study of 17 commonly used synthetic “forever chemicals” has shown that these toxic substances can be easily absorbed through human skin.
New research results published in Environment International, proves for the first time that a wide range of PFAS (perfluoroalkyl substances) – chemicals that do not break down in nature – can penetrate the skin barrier and enter the body’s bloodstream.
PFAS are widely used in industry and in consumer products ranging from waterproof clothing and school uniforms to personal care products due to their water- and stain-repellent properties. While some substances have been banned by government regulations, others are still widely used and their toxic effects are not yet fully studied.
PFAS are already known to enter the body through other routes, such as inhalation or ingestion through food or drinking water. They are also known to cause adverse health effects, such as reduced immune response to vaccinations, impaired liver function and lower birth weight.
It was generally believed that PFAS cannot penetrate the skin barrier, although recent studies have shown a link between the use of personal care products and PFAS concentrations in human blood and breast milk. The new study is the most comprehensive assessment to date of PFAS absorption through human skin and confirms that most of them can enter the body this way.
The study’s lead author, Dr Oddný Ragnarsdóttir, carried out the research while studying for her PhD at the University of Birmingham. She explained: “The ability of these chemicals to be absorbed through the skin has previously been dismissed because the molecules are ionised. The electrical charge that gives them the ability to repel water and stains probably also made them unable to penetrate the skin membrane.”
“Our research shows that this theory is not always true and that absorption through the skin can actually be a significant source of exposure to these harmful chemicals.”
The researchers examined 17 different PFAS. The compounds selected were among the most commonly used and best studied for their toxic effects and other ways people might be exposed to them. Most importantly, they correspond to chemicals regulated under the EU Drinking Water Directive.
For their experiments, the team used 3D models of human skin – multilayered, lab-grown tissues that mimic the properties of normal human skin, allowing the study to be conducted without animal testing. They used samples of each chemical to measure what proportions were absorbed, not absorbed or retained in the models.
The team found that 15 of the 17 PFAS tested had significant absorption through the skin—at least 5% of the exposure dose. At the exposure doses studied, absorption into the bloodstream of the most highly regulated PFAS (perfluorooctanoic acid (PFOA)) was 13.5%, with an additional 38% of the applied dose remaining in the skin and potentially absorbed into the bloodstream over the longer term.
The amount absorbed seemed to correlate with the length of the carbon chain in the molecule. Substances with longer carbon chains showed lower absorption rates, while compounds with shorter chains, introduced to replace PFAS with longer carbon chains such as PFOA, were more easily absorbed. The absorption of perfluoropentanoic acid, for example, was four times higher than that of PFOA at 59%.
Study co-author Dr Mohamed Abdallah said: “Our study provides initial insights into the importance of dermal absorption as an exposure route for a wide range of persistent chemicals. Given the large number of PFAS in existence, it is important that future studies aim to assess the risk of a broad 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 understand how important contact with these chemicals through the skin might be and which chemical structures might be most easily absorbed. This is important because we are seeing a trend in industry towards chemicals with shorter chains as these are considered less toxic. However, the downside might be that we absorb more of them, so we need to know more about the risks associated with them.”