07-08-2025
So Your Workout Clothes Are Made of Plastic. Now What?
It's true that some synthetic fabrics commonly used in workout clothing, such as polyester, nylon, and spandex, might expose you to a range of potentially harmful chemicals.
'These chemicals are not necessarily present in all synthetic fabrics, but they are commonly used or can be residues from manufacturing processes associated with these materials,' said José Domingo, professor emeritus of toxicology at the Universitat Rovira i Virgili School of Medicine in Spain, in a written response.
They may include skin irritants that could trigger contact dermatitis, such as azobenzene disperse dyes, which are commonly used to color synthetic fabrics, and formaldehyde releasers, which are often used in wrinkle-free textiles.
Synthetic clothing may also contain some endocrine-disrupting chemicals, which are linked to a range of health impacts that affect reproduction, physical development, neurodevelopment, metabolism, and immune system function, as well as cancer risk. These chemicals include phthalates; bisphenols such as BPA; benzothiazoles, used in chemical processing; antimony, a catalyst residue often found in polyester; and aromatic amines from dyes.
Some may also contain PFAS, a broad class of chemicals linked to cancer, pregnancy complications, and weakened immune function, though they may also appear in other types of fabrics. (And, in fact, some states have already started banning PFAS in clothing.)
The presence of all these chemicals 'depends on specific manufacturing processes, dyes, and finishing treatments used,' said Domingo.
And not all synthetic textiles are alike. There are petroleum-based fabrics, including polyester, nylon, spandex, and acrylic, which are often found in clothing items like leggings and sports bras. Plasticized bio-based fabrics, such as some bio-based nylon and polyamide, use corn or other plant materials but may be mixed with petroleum-based plastic and chemicals (similar to bio-based plastic bags), said Alden Wicker, a journalist who covers environmental health and sustainability in fashion.
Cellulosics, such as rayon (sometimes called lyocell or modal), are another category of synthetics. They may be used in exercise clothes, as well as blouses, dresses, slacks, and other garments. These are made primarily from woody plant pulp that has been chemically dissolved and processed into a textile. From an individual health perspective, cellulosics may be less concerning than petroleum-based or bio-based fabrics, Wicker said, though they do require chemical-intensive processing.
Many experts I spoke with said that natural fibers are less likely to have high concentrations of some of those potentially harmful chemicals, like azobenzene disperse dyes and antimony. But broadly, there's no guarantee that clothes made with 100% cotton or other natural fibers are automatically lower in harmful chemicals than synthetic ones, said Miriam Diamond, an environmental scientist and professor at the University of Toronto's School of the Environment. Diamond noted that even 100% cotton has been found to sometimes contain chemicals, such as bisphenol.
Complicating matters, manufacturers aren't required to disclose chemicals in clothes, and 'they may not even know themselves given the complexities of global supply chains,' said Justin Colacino, associate professor of environmental health sciences at the University of Michigan, in an email interview.
