Trihydroxystearin is the triester of glycerin and hydroxystearic acid. It is used as a skin conditioning agent, a solvent, and as a viscosity increasing agent in cosmetic formulations at concentrations up to 5%. In acute oral toxicity studies in rats, no deaths were reported at a dose of 5 g/kg. Trihydroxystearin was reported to be a mild ocular irritant, but not a skin irritant in animal tests. Ames test results indicate that the ingredient is not mutagenic. Clinical testing found no skin irritation. Although the data on Trihydroxystearin are limited, the Cosmetic Ingredient Review (CIR) Expert Panel had previously conducted a safety assessment of Glyderyl Stearate and Hydroxystearic Acid. These data indicate no mutagenic, carcinogenic, or teratogenic effects in animals, and no irritation or sensitization in clinical tests. The data on these two ingredients are considered relevant to the assessment of Trihydroxystearin because of the chemical similarity of the ingredients. The data on Glyceryl Stearate and Hydroxystearic Acid are also consistent with the limited data that are available on Trihydroxystearin itself. Therefore, based on the available animal and clinical data in this report, which includes study summaries from earlier safety assessments of Hydroxystearic Acid and Glyceryl Stearate and Glyceryl Stearate/SE, the Expert Panel concludes that Trihydroxystearin is safe as used in cosmetic formulations.