Nylon

Nylon is a synthetic polyamide made by polymerizing petroleum-derived monomers; in Nylon 6 the building block is caprolactam, and not every unit fully links during polymerization, so residual caprolactam monomer can remain in and migrate out of the fiber. Manufacturing and finishing chemicals, not the polymer backbone, drive most of its wearer-health concerns.

Nylon is dyed almost exclusively with disperse dyes, the leading cause of textile allergic contact dermatitis; these dyes do not bond to the fiber, so their small lipophilic molecules migrate onto your skin, with Disperse Blue and Disperse Orange dyes showing positive patch tests in roughly 5 to 7 percent of chronic-eczema patients, worse where clothing rubs and you sweat. Nylon is also one of the heaviest microplastic shedders of any fabric, releasing hundreds of thousands of fibers in a single wash and shedding directly onto your skin and into the air you breathe as you move. Those microfibers can carry dyes, plasticizers, and finishing additives that leach out on contact.

Look for OEKO-TEX STANDARD 100 certification, which limits disperse-dye allergens and residual monomers, and prefer undyed or light-colored, tightly woven nylon over deeply dyed stretch pieces worn against the skin.

Nylon is fossil-derived, non-biodegradable, and a major source of microplastic fiber pollution in water and air.