As research uncovers the abundance of microplastics—in everything from Antarctic snow to our produce—we’re also learning more about how these tiny pieces of plastic harm our health. These microscopic particles can get into our bodies via water and air, and they’re not only a health risk on their own. They also carry toxic chemicals, which can then get into our bloodstream through our skin.

Plastic is full of chemicals. In some cases, they’re used to make plastics flame retardant—couches, carpets, building materials, electronics, and so on. These chemicals have been linked to cancer, developmental problems, and other health effects in humans. Some of them have since been banned, like brominated flame retardant, which has been banned in the U.S. since 2004—but they’re still prevalent in pollution and in older products that shed or leach out microplastics.

Researchers at the University of Birmingham previously found that microplastics leach such chemicals into human sweat. We’re exposed to microplastics in a variety of ways; plastic fabrics and textiles, whether on clothes or furniture, shed microplastics when worn or touched. Microplastics are in indoor dust. Cosmetic products can contain microplastics, which come in direct contact with our skin. Even plastic baby bottles shed microplastics when warmed up.

Now a study published in the journal Environment International found that those chemicals can cross the skin barrier into our bodies. How much of these chemicals your skin absorbs can depend on how sweaty you are (more “hydrated” skin absorbs more chemicals), but the researchers found that skin can take as much as 8% of the exposed chemical.

“Microplastics are everywhere in the environment, and yet we still know relatively little about the health problems that they can cause. Our research shows that they play a role as ‘carriers’ of harmful chemicals, which can get into our bloodstream through the skin,” says lead author Ovokeroye Abafe in a statement. “These chemicals are persistent, so with continuous or regular exposure to them, there will be a gradual accumulation to the point where they start to cause harm.”

The research team conducted their study by using 3D human skin models, rather than animals or human test subjects. Over a 24-hour period, they exposed the models to two common microplastics containing polybrominated diphenyl ethers, a class of brominated flame retardants. Researchers created their own microplastics by grinding down polyethylene and polypropylene and then applied these onto the surface of the skin models. The researchers say it’s the first experimental evidence that chemicals that are additives in microplastics can get into our bloodstream through our sweat and skin. They plan on conducting more research to understand other ways microplastics could bring toxic chemicals into our bodies, and how we might mitigate that exposure risk.

Flame retardants are just one type of toxic additive. Plastics can also be full of PFAS, or forever chemicals; phthalates, which make plastic more durable; BPA, which hardens plastic; and more. All of these have been linked to adverse health effects, like increased blood pressure, cardiovascular diseases, endocrine disruption, and more. As pieces of those plastics break off into microplastics, those microplastics also carry the toxic chemicals.

The researchers’ results, they wrote, “provide important experimental evidence for regulators and policymakers to legislate for microplastics and safeguard public health against such exposure.”