PFAS can penetrate the skin and reach the bloodstream, according to the paper Dermal bioavailability of perfluoroalkyl substances using in vitro 3D human skin equivalent models, published in June 2024 on the academic journal Environment International and written at the University of Birmingham by Oddný Ragnarsdóttir, Mohamed Abou-Elwafa Abdallah, Stuart Harrad.
Researchers have examined the skin absorption of 17 perfluoroalkyl substances (so-called PFAS), using in vitro 3D artificial models of human skin. They discovered that PFAS with the shortest chains are absorbed more easily than the ones with longer chains, which instead tend to accumulate in skin tissues.
The skin, a barrier: but to which extent?
PFAS, known also as “forever chemicals” because of their strong persistence, are chemical substances created by humans to make products and coatings that repel grease, water or heat. They are a class of organic chemical compounds characterized by the presence of carbon-fluorine bonds and are very harmful to both the environment and human health. They can be found in air, water, food, and they are related to an increased incidence of disease. The study of the University of Birmingham shows that the skin can also be a vehicle with which PFAS penetrate the human body, for example through cosmetics, such as sunscreens, hand disinfectants or waterproof mascara, which contain them.
“We know you can be exposed to PFAS in a variety of ways,” explains to Renewable Matter Professor Stuart Harrad, one of the authors of the study. “PFAS have been used in fabrics, for clothing for example, which do come into contact with the skin. The question is how much of that is present, and how much it is absorbed by the skin. Just because PFAS are present in a product that comes into contact with the skin, it doesn't mean that they actually penetrate through it, because fortunately, the skin is an excellent protective layer. We tried to understand whether the fact that PFAS might be present in cosmetics translates into a measurable dose that gets through the skin”
The research is still limited on these topics. However, there is a previous study involving a human volunteer to test the absorption of a certain type of PFAS (3C4-perfluorooctanic acid) specifically inserted into a sunscreen to monitor its absorption by the skin. “They found that a large proportion of the substance did end up in the person’s blood and the concentration peaked about three weeks after”, Harrad adds. “Rather than using human volunteers or animals, which obviously raises ethical questions, we've used this cultured human skin, models of human skin capable of replicating most of the functions of human skin.”
It is the first official study of this kind, conducted on artificial 3D skin. On that skin, researchers have put a predetermined quantity of 17 different PFAS, dissolved in methanol, for around 24-36 hours. They later measured the level of absorption for each substance, how much was left on the surface and how much inside of the skin tissues. Also, the rapidity and permeability with which every substance penetrated the skin was also measured. Within the 17 PFAS tested, the team discovered that at least 15 substances showed a substantial dermal absorption: at least 5% of the exposure dose. So, the final discovery is that yes, PFAS can be absorbed and reach the blood vessels, but with variables related to the length of the chemical chains that make up their structure. Compounds that have shorter carbon chains can easily penetrate the skin barrier and accumulate in the blood, the study explains. Compounds with longer chains struggle to penetrate, though it may not be impossible.
“One thing that we haven’t tested yet and we would like to, is to take some PFAS-containing fabrics, apply them to a skin model and see how much of that goes through”, adds Harrad. This is because PFAS are contained in many fabrics, such as the water repellent ones used in waterproof clothing.
Consequences for consumers
“I think our study is a big step forward because it tells us how much of these things are likely to be absorbed”, explains Harrad. “But what we don't know is really how much of these things are actually present in the products with which we come into contact. So that's probably one of the next steps that would be very useful to take, in terms of research: extend the range of PFAS to be tested for absorption.” On the other hand, it is not known exactly how large the class of PFAS is: the search for new substances belonging to this group is still ongoing. According to data provided by the EPA (U.S. Environmental Protection Agency) in 2022, more than 15,000. The European Chemicals Agency (ECHA) is currently discussing the regulation of chemicals in Europe.
“I think my advice for the people would always be to be an active consumer and if there is something that concerns you, to look into it and to take it into consideration, for example by buying PFAS-free products”. Adds Harrad. “I think it is necessary to review how things are labelled, to make it easier for people to understand. And this is not something that a consumer can do directly, you have regulators doing that. Consumers can make a fuss and try to get their governments to intervene.”
This article is also available in Italian / Questo articolo è disponibile anche in italiano
Cover image: Nataliya Melnychuk, Unsplash