Older black man with sweaty t shirt throwing basketball in the air on an urban basketball court
Credit: Ketut Subiyanto

Human sweat has been found to leach toxic chemicals out of microplastics and are potentially making them available to be absorbed through skin, a new study has shown.

A team from the University of Birmingham looked at microplastics taken from common forms of plastic and tested them with a synthetic sweat in a lab. They analysed the bioaccessibility of brominated flame retardants (a class of chemical used to improve the performance of plastics) after the microplastics have come into contact with sweat. They found that in all examples, the toxic chemicals leached out of the plastic particles and as a result, these chemicals may be absorbed through layers of skin.

The paper, published in Environmental Science and Technology found that polyethylene microplastics were the worst for bioaccessibility of the flame retardant chemicals which have been previously found in animal studies to cause adverse health effects including neurotoxicity, reproductive toxicity and cancer.

Dr Ovokeroye Abafe, Marie-Curie Research fellow at the University of Birmingham and first author of the paper said:

“The study provides new insights into the risk that arises from our exposure to microplastics in daily life. Our skin is constantly exposed to microplastics either through our clothing, cosmetics, indoor and outdoor dust particles, or even from the air.

“We have shown the first experimental evidence that toxic additive chemicals can leach out from microplastics to our sweat and become available for absorption through the skin. This raises concern over potential adverse effects of these chemicals, including endocrine disruption, neurotoxicity, obesity, and cancer.

Our skin is constantly exposed to microplastics either through our clothing, cosmetics, indoor and outdoor dust particles, or even from the air.

Dr Ovokeroye Abafe

Some cosmetics increase the risk


Antiperspirants and foundations were also found to increase the bioaccessibility of the toxic chemicals, contrary to expectations.

In tests of four cosmetics alongside the mixture of the microplastics and synthetic sweat, sunscreen and moisturiser had no impact on the bio-accessibility of the flame-retardant chemicals leaching out, but that antiperspirants and foundations increased the fraction of one of the chemicals known as decabrominated diphenyl ether (BDE-209) by approximately 20% and 10% respectively.

They also found that the size of microplastics played critical role in the amount of the chemicals that are released from the particles into sweat. The team compared 4mm pellets and 0.45mm pellets, and found that the bioaccessibility from the smaller pellets was approximately doubled.

Dr Mohamed Abdallah, principal investigator for the project, Associate Professor of Environmental Sciences at the University of Birmingham and a co-author of the paper said:

“Because toxic flame-retardant chemicals are hydrophobic, it wasn’t clear if they would leach out of the microplastic to human sweat. However, human sweat is a complex mixture that contains oily components known as sebum, which facilitated the leaching of toxic chemicals from microplastics, rendering them available for absorption through the skin.

“With this new evidence, policy makers need to seriously consider the risks of microplastics and human contact with them on a regular basis. We will be continuing to research how these chemicals that can be leached through contact with sweat may be absorbed by human skin on a daily basis.”