Written by: Denise John, PhD

Published on: May 9, 2024

We’ve come across some alarming headlines in the last year suggesting that workout clothes potentially expose us to endocrine-disrupting chemicals. Before throwing out all our workout gear, we paused—and decided to investigate. Here’s what we found after digging into the research and talking to five experts in environmental health, plastic toxicity, and bioengineering.

What are microplastics?

As the name suggests, microplastics are tiny particles of plastic, less than five millimeters long. They fall into two categories: Primary microplastics, which are microplastics directly released into the environment as small particles. And secondary microplastics, which come from larger plastics (like bags, bottles, or fishing nets) that break off into tiny pieces over time.

The world’s largest source of primary microplastics is clothing—accounting for an estimated 35 percent. (Car tires are the second largest primary microplastic source.) About 70 percent of clothes produced around the world are made from plastic (synthetic) materials: polyester, nylon, acrylic, and elastane (a polyurethane-polyurea copolymer that’s also known by its brand names, Lycra and spandex). Tiny pieces of synthetic fabric break off from clothing—due to friction caused by washing and wearing—creating microplastics.

What do microplastics have to do with endocrine-disrupting chemicals?

Because of their chemical structure, microplastics attach easily to known endocrine-disrupting chemicals—including dioxins, pesticides (like DDT), brominated flame retardants, phthalates, and bisphenol A (BPA)—in the environment. That means that the endocrine disruptors go everywhere that microplastics do: domestic water systems, rivers, lakes, oceans, and the air.

Eventually they make their way into our bodies—scientists have found evidence of microplastics and nanoplastics (smaller pieces of microplastics) in human blood, intestines, lungs, kidneys, livers, hearts, reproductive organs, and even placentas. They can disrupt critical reproductive and metabolic hormone-regulating connections, like the hypothalamic-pituitary-ovarian axis, as well as the HP-testicular, HP-thyroid, and HP-adrenal axes, for example. Some studies suggest that microplastics disturb the immune system’s normal response and damage immune cells.

Why are workout clothes of particular concern?

Some of the same harmful chemicals that attach to microplastics from the environment, like BPA, are also found in clothes that are made from synthetic materials, according to Kizzy Charles-Guzman, the chief executive officer at the Center for Environmental Health, a nonprofit organization that works to reduce people’s exposure to toxic chemicals. These synthetic materials are not unique to workout clothing, but how we wear workout garments may mean that they pose a greater health risk than other clothing does, at least hypothetically.

For example, workout clothes, like sport bras and leggings, are designed to fit tightly—directly against our skin. Research shows that microplastics can enter the body through sweat glands, hair follicles, and skin wounds; the close contact could increase the chances of harmful chemicals getting into our bodies. Plus, we probably sweat in workout gear more than we do in any other kind of clothing—preliminary data suggest that sweat may increase the chances of microplastics and toxic chemicals moving through the skin into the body.

If and how our workout clothes are leaching microplastics and endocrine disruptors directly into our bodies is theoretical, though. “Our understanding of the full impact of microplastics as carriers of endocrine disruptors—that’s still evolving,” says Jeff Karp, PhD, a Harvard Medical School professor and MIT bioengineer. We need more investigation to elucidate the exact impact on our health—and true solutions will follow. “Any time there’s a problem that gets to be well understood in society, it then creates this crucible moment to focus innovation on it,” Karp says.

Read the full article here.