OEKO-TEX Standard 100 certifies that a textile product (and every component — yarn, button, zipper, lining) has been tested for substances harmful to human health. The criteria include limits on formaldehyde, heavy metals, pesticides, phthalates and azo dyes.
Standard 100 is a safety certification — not an organic, fair-trade or environmental one. For environmental processing standards, look for OEKO-TEX STeP or GOTS.
How the four product classes work. Limits get stricter the closer a textile sits to skin, and the strictest class of all is for babies. Product Class I covers items for children up to three years old — including formaldehyde at effectively non-detectable levels and tighter pH and colourfastness requirements. Class II covers articles worn next to skin such as underwear, bedding and t-shirts. Class III covers items worn away from skin like outer jackets. Class IV covers furnishing materials such as curtains and upholstery. A Class I certificate is a meaningfully higher bar than a Class IV one, so read the class printed under the label number, not just the logo.
What is actually tested. The test catalogue is revised annually and now runs to hundreds of regulated and non-regulated substances: banned azo colourants that cleave to carcinogenic arylamines, formaldehyde, extractable heavy metals (lead, cadmium, nickel, chromium VI), pentachlorophenol and other chlorinated phenols, phthalate plasticisers, organotin compounds, PFAS, flame retardants, biocides, allergenic and carcinogenic disperse dyes, plus skin-friendly pH and colourfastness to saliva, perspiration and rubbing. Every component is tested individually — a certified fabric with an uncertified zip does not qualify.
How to verify a certificate. Each certificate carries a unique number and the issuing institute, for example "20.HTR.12345 Hohenstein HTTI". Enter that number in the OEKO-TEX label check on oeko-tex.com and you get the holder, the article scope, the product class and the validity period. Certificates last twelve months and must be renewed with fresh testing, so an out-of-date number on a current product is a red flag.
What it does not tell you. Standard 100 says nothing about organic fibre content, water and energy use in dyeing, wastewater discharge, carbon footprint, animal welfare or wages. It is a finished-article chemical-safety test, so a conventionally grown, heavily irrigated cotton t-shirt dyed in a polluting mill can carry the label legitimately as long as the finished cloth passes the residue limits. That gap is exactly what the sibling standards close: OEKO-TEX STeP audits production facilities on chemical management, environmental performance and social conditions; MADE IN GREEN combines Standard 100 testing with STeP facility auditing and gives a traceable product ID; ORGANIC COTTON adds verified organic fibre with GMO testing.
How it compares to GOTS. GOTS is the broader standard — organic fibre content, restricted process chemistry, wastewater treatment and ILO labour criteria across the whole chain. OEKO-TEX Standard 100 is narrower but applies to any fibre, including synthetics that GOTS cannot cover. For bedding, baby clothes and underwear, GOTS plus OEKO-TEX is the strongest pairing; for technical or synthetic textiles, OEKO-TEX MADE IN GREEN is usually the best signal available.