An inescapable form of human pollution is seeping into our bodies in ways we never fully realized.

University of Birmingham scientists have shown using models of human tissue that 'forever chemicals' like PFAS (per- and polyfluorinated alkyl substances) are surprisingly capable of passing through our skin.

When these stubbornly persistent materials were first created more than half a century ago, companies like DuPont – the maker of Teflon – were aware that some of these non-stick, waterproof substances were "highly toxic" when inhaled and "moderately toxic" when ingested.

As far back as 1961, secretly held company documents show that Teflon's head toxicologist knew that some types of long-lasting PFAS should not make contact with the skin.

Fast forward to 2024, and independent scientists are only now beginning to show that the skin is a significant source of exposure for some of the most widespread and well-studied PFAS chemicals out there.

Today, PFAS are found in numerous products designed especially for our dermis, including cosmetics as ubiquitous as sunscreen, moisturizers, and cleansers.

"The ability of these chemicals to be absorbed through skin has previously been dismissed because the molecules are ionized," explains environmental scientist Oddný Ragnarsdóttir.

"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."

Experiments conducted by Ragnarsdóttir and her team suggest that is not necessarily true in all cases.

Today, more than 12,000 known PFAS variants are available on the market, but at this point, scientists do not know enough about how cosmetic products relate to forever chemicals in the bloodstream, or if those pollutants have toxic effects in the body, and at what level of exposure.

To focus their efforts, the researchers analyzed 17 of the most common and widely studied chemicals of the lot. Each of the substances was applied to a 3D human skin model, designed to mimic real human skin, and the team watched to see which were absorbed.

Out of the PFAS tested, 15 seeped into the skin model within 36 hours. One particularly worrisome chemical that was tested, called PFOA (perfluoro octanoic acid), is toxic enough to have been phased out of production in the US in the early 2000s. But not before it spread far and wide in the environment. It regularly shows up in tap water still.

In 2023, PFOA was banned globally under the UN Stockholm Convention due to its carcinogenic effects when ingested or inhaled. It now seems the chemical can also be absorbed through the skin.

Of all the PFOA that was smeared onto the study's model, roughly 13.5 percent made it into the bloodstream. What's more, 38 percent was left soaked into the skin, where it could easily enter the bloodstream later.

One recent study, which involved a single male volunteer, "unambiguously demonstrated" that if PFOA is present in sunscreen (as it sometimes is), forever chemicals from that product can absorb into the skin and bloodstream.

"It is very likely that a part of the absorbed [PFOA] is distributed from blood to other fluids and tissues," suggest the authors of the recent skin model study.

"However, only very few reports dealing with PFAS levels in organs and blood are available for humans."

Today, PFOA has been replaced by forever chemicals with shorter carbon chains, but worryingly, the recent research suggests the longer the chain, the less easily it is absorbed into the skin.

One of these newer, shorter-chained chemicals, called perfluoropentanoic acid (PFPeA), was absorbed into the skin at four times the rate of PFOA.

PFPeA, which is commonly used in food packaging, has shown systemic toxicity in mouse models when applied to the skin. But testing such chemicals directly on humans is ethically fraught.

A 3D skin model provides a useful study route without having to put anyone at risk.

Earlier this year, the technique was used to show that some other chemicals that are notoriously difficult to break down and which are used in toxic flame retardants, called polybrominated diphenyl ethers (PBDEs), can leech into the skin and enter the bloodstream within a day.

Many questions remain around forever chemicals and their passage through the skin, but when even toxicologists are ditching certain cosmetic brands for fear of PFAS exposure, it's time to pay attention.

The study was published in Environment International.