Flame retardants apparently save lives, but in addition to foiling potential fires, many of these chemicals also may be slowly sickening the people they were meant to protect.

Research has linked flame retardants with serious health risks, including hormone disruption and cancer, although details about their effects in humans remain limited. Those described as 'forever chemicals' tend to resist degradation and accumulate in body tissues.

According to the US Centers for Disease Control and Prevention (CDC), humans are commonly exposed to flame retardants by eating contaminated food or breathing contaminated air.

With many plastic products, including foam in padding, casings for appliances, and wire insulation containing the products, microplastics from their breakdown are becoming a greater cause for concern.

A new study by researchers from Brunel University London and the University of Birmingham in the UK suggests there is also another, previously overlooked way in which people can be exposed to certain flame retardants: absorbing them through our skin.

Using a 3D-printed model of human skin, the study's authors showed how a group of flame retardants known as polybrominated diphenyl ethers (PBDEs) can be sucked up through the skin and enter the bloodstream within 24 hours.

The phenomenon occurs when skin comes into contact with PBDE-laden microplastics, they report, with sweatier skin absorbing the compounds more efficiently than dry skin.

The researchers note that this is the first study to identify skin absorption as a potentially harmful mode of exposure to PBDEs.

"We confirm for the first time that human exposure via skin contact with microplastics containing PBDEs contributes to the human body burdens of these toxic chemicals," says lead author Ovokeroye Abafe, an environmental chemist and exposure scientist at Brunel University London.

illustration of experiments that found human skin can absorb PBDEs
(Brunel University London)

PBDEs were developed in the 1970s and soon became ubiquitous, helping reduce the fire hazards posed by a wide range of consumer products.

Some of the flame retardants have been banned in recent years amid mounting evidence of risks, but others are still commonly found in consumer products.

Plastics are already an environmental scourge, largely due to their prevalence and persistence. As plastic items degrade into microplastics, tiny plastic chunks lodge in human bodies, raising concerns about possible health effects.

The public health implications of microplastics remain unclear, but with plastics often containing additives associated with cancer risk and endocrine disruption, researchers are keen to understand the true risk.

Abafe and his colleagues note that previous research has shown chemicals can leach from microplastics into human sweat, but this is the first scientific evidence that PBDEs within microplastics can cross the skin barrier and enter the bloodstream.

"These results provide important experimental evidence for regulators and policy makers to legislate for microplastics and safeguard public health against such exposure, which contributes to the human body burdens of toxic additive chemicals linked with causing cancer and disruption of the endocrine system," Abafe says.

To reveal these findings, the researchers used 3D-printed models of human skin, which are made from human keratinocytes, the primary cells in our epidermis.

The skin model absorbed up to 8 percent of the exposure dose, though less than 0.1 percent of the exposure dose made it into the bloodstream. While it's not clear what dangers this poses in a real-world scenario, it's a proof-of-concept that shows the skin isn't necessarily a total barrier to the compounds' entry.

Given the continued prevalence of PBDEs, and the existing evidence of their potential danger, this new discovery warrants urgent action to protect public health, Abafe says.

More research is still needed, he adds, to flesh out our understanding of this discovery and shed light more broadly on the many other chemicals lurking in the hidden flood of microplastics all around us.

"Unfortunately, there are myriads of toxic additive chemicals, ranging from plasticisers to stabilizers in microplastics, some of which are not regulated, that can potentially find their way into the human system," Abafe says.

The study was published in Environment International.