Polyester vs Cotton

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.

Most field pesticide residue degrades or washes out during processing, so it is the finishing chemistry on the finished garment you wear that matters most. Conventional cotton labeled wrinkle-free, easy care, or no-iron is frequently treated with formaldehyde-based durable-press resins, a recognized human carcinogen that off-gasses and is linked to contact dermatitis and skin irritation. Reactive and azo dyes can also leave residue that touches your skin all day. The upside: untreated cotton is genuinely breathable and lets air move against your skin, which is why it stays comfortable in heat.