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.