| Summary: | Sodium thioglycolate is used in the cosmetic industry as an antioxidant, depilating agent, hair waving/straightening agent, and reducing agent. Its primary cosmetic use is in depilatories. Sodium thioglycolate is also used as an analytical reagent and in bacteriology for the preparation of thioglycolate media. Sodium thioglycolate was nominated by the National Cancer Institute for toxicology studies due to its high production volume and widespread occupational and consumer exposure to thioglycolic acid and its salts and esters, including significant female exposure in personal care products. Male and female F344/N rats and B6C3F1/N mice were administered sodium thioglycolate (approximately 99% pure) in a vehicle of 95% ethanol:deionized water (1:1) by application to shaved dorsal skin for 16 (rats) or 17 (mice) days or for 3 months. Genetic toxicology studies were conducted in Salmonella typhimurium and mouse peripheral blood erythrocytes. In the 3-month study in mice, groups of 10 males and 10 females were dermally administered 0, 22.5, 45, 90, 180, or 360 mg/kg sodium thioglycolate in 95% ethanol:deionized water (1:1) 5 days per week for 3 months. Nonneoplastic lesions were limited to the site of application and included minimal to mild epidermal hyperplasia, hyperkeratosis, sebaceous gland hypertrophy, and inflammation. Sodium thioglycolate was not mutagenic in S. typhimurium strains TA98, TA100, TA1535, or TA1537 when tested with or without liver S9 activation enzymes. Dermal exposure to sodium thioglycolate for 3 months resulted in a small but significant increase in micronucleated normochromatic erythrocytes in peripheral blood of female mice; results in male mice were negative. In summary, sodium thioglycolate caused minimal to mild nonneoplastic lesions at the site of application in rats and mice after 3 months of exposure through the skin
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