Rayon vs Cotton
Rayon is the cleaner choice. It scores 22 versus Cotton's 30 on the Toxome health scale, where lower is safer for your skin.
Rayon
Because rayon is viscose, it carries the same profile. The acute danger is to workers handling carbon disulfide, which causes nerve and cardiovascular damage at occupational doses. What reaches you is residue: the chemical substances used in production can remain in the fabric and provoke allergic reactions or contact dermatitis on skin contact, and formaldehyde-based finishing agents are sometimes added for wrinkle resistance, leaving residues that irritate sensitive skin. Rayon is breathable and absorbent, so it wears cool, but unbranded or uncertified pieces are the ones most likely to carry leftover finish.
Full rayon guide →Cotton
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.
Full cotton guide →Rayon. Standard rayon manufacturing emits toxic chemicals and contributes to deforestation pressure on endangered forests.
Cotton. Conventional cotton is water- and pesticide-heavy in cultivation, while organic systems sharply cut chemical inputs.