The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area has evaluated thioglycolic acid and its salts to derive a maximum concentration at the workplace (MAK value), considering all toxicity endpoints. Available publications are described in detail. As the critical effect of thioglycolic acid is local irritation, but there are no inhalation studies available for this substance, no MAK value can be derived and thioglycolic acid is listed in Section II b of the List of MAK and BAT Values. Thioglycolates are slightly irritating to the skin and eyes of rabbits. In the 13‐week gavage study in rats changes in biochemical parameters and hepatocellular microvacuolization are found in the females at 20 mg/kg body weight and day and above. The NOAEL is 7 mg sodium thioglycolate/kg body weight and day. An amplification of the effects with increasing exposure duration cannot be excluded. As the irritation potency is low, a MAK value of 2 mg thioglycolate/m3 for the inhalable fraction can be derived. As the critical effect is systemic, thioglycolates are assigned to Peak Limitation Category II. The default excursion factor of 2 is set as no half‐life in blood is known. In rats, the oral NOAEL for developmental toxicity is 75 mg ammonium thioglycolate/kg body weight and day and the dermal NOAEL is 100 mg sodium thioglycolate/kg body weight and day. The dermal NOAEL for developmental toxicity in rabbits is 65 mg sodium thioglycolate/kg body weight and day, the highest dose tested. Scaling of these NOAEL to a concentration in the work‐place air shows that damage to the embryo or foetus is unlikely when the MAK value or the BAT value is observed and thioglycolates are classified in Pregnancy Risk Group C. Thioglycolic acid and its salts are not genotoxic. In a carcinogenicity study with mice given sodium thioglycolate doses of up to 13.3 mg/kg body weight twice a week dermally, tumour incidences are not increased. In humans, thioglycolic acid and its salts have a low potential for contact sensitization. A local lymph node assay, however, indicates a contact sensitization potential for ammonium thioglycolate. Thioglycolic acid and its salts are therefore designated with an “Sh” notation. Skin contact may contribute significantly to systemic toxicity and thioglycolic acid and its salts are designated with an “H” notation.