Polyester vs Nylon

When polyester contacts your sweat, a fraction of that antimony mobilizes into the moisture against your skin; antimony trioxide is classified by IARC as a possible human carcinogen, and exposure rises in tight, warm activewear. Polyester is also the workhorse of disperse-dye allergy, the most common cause of textile contact dermatitis, with the dye migrating onto skin worst where you sweat and rub. On top of that, polyester sheds microplastics onto your skin and into household air, and consumer testing has flagged bisphenol A (an endocrine disruptor) in polyester athletic wear at many times the safe limit. The dose from any one garment is small, but you wear it constantly and sweat into it.

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.