Fibers can contain a wide range of hazardous substances, including dyes, plasticizers, per- and polyfluoroalkyl substances (PFAS), and metals. Microfibers also act as important vectors of chemical exposure through inhalation and dermal contact, underscoring the need for updated risk assessments.

Disperse dyes, widely used in synthetic fibers, are a primary cause of fiber-related allergies and are medically significant. Azo dyes, for instance, are synthesized using aromatic amines (AAs), some of which are carcinogenic, genotoxic, or allergenic. Certain azo dyes can also release AAs within the body. AAs were detected in 17% of 153 clothing samples in Switzerland, with concentrations reaching 622 mg/kg. In addition, dozens of non-regulated AAs with mutagenic potential have been identified in azo dyes. In another study, 120 women's underwear samples were analyzed, and 18 exceeded EU and Chinese health standard limits. As a result, the EU bans dyes that release 22 known carcinogenic AAs.

Beyond dyes, fibers may contain quinoline, bisphenols (BPAs), benzothiazoles (BTHs), and benzotriazoles (BTRs). Quinoline, used in dye production, is a possible carcinogen and skin irritant and was detected in 29 of 31 clothing samples, accounting for about half of all measured chemicals. Bisphenols are known endocrine disruptors; BPA was found in 82%, BPS in 53%, and benzophenone-3 in 70% of 79 textile samples, with infant socks showing the highest exposure levels. Benzothiazoles may cause irritation, allergies, or pose cancer risks, while benzotriazoles are associated with endocrine disruption and reproductive effects. Analyses of clothing items, including children's garments, have detected multiple types of BTHs and BTRs, with BTHs identified as the most common chemicals in textile samples. Some infant bodysuits exhibited particularly high concentrations of BTRs.

Although initiatives such as OEKO-TEX® and GOTS seek to reduce chemical risks, enforcement remains uneven. Labeling alone does not ensure safety. Even when fibers are organically grown, downstream processing steps such as bleaching, chemical finishing, or hydrogen peroxide treatment can introduce hazardous substances, leading to exposure risks comparable to those of conventionally produced fibers. For example, a baby bodysuit labeled "organic cotton" with an ecolabel was found to contain benzothiazoles.