Biotin is a water-soluble vitamin used as a hair-conditioning agent and a skin-conditioning agent in many cosmetic products at concentrations ranging from 0.0001% to 0.6%. Although Biotin does absorb some ultraviolet (UV) radiation, the absorption shows no peaks in the UVA or UVB region. Biotin is rapidly metabolized and excreted in urine. Little acute oral toxicity is seen in animal tests. Short-term and subchronic toxicity studies likewise found no evidence of toxicity. Although intradermal injection of a small quantity of Biotin (0.1 ml) into guinea pig skin did not produce skin irritation, Biotin (0.1% at pH 7.3) did produce slight, transient ocular irritation in rabbit eyes. Biotin was not mutagenic in bacterial tests, but positive results were found in a Tradescantia micronucleus test. There was evidence of an increase in the number of resorptions in rats receiving Biotin by subcutaneous injection, with concomitant decreases in fetal, uterine, and placental weights. Another study of mice receiving Biotin orally or by subcutaneous injection found no differences between control and treatment groups. Although there is one case study reporting an urticarial reaction in the literature, there are a very large number of individuals exposed to Biotin on a daily basis, and there is not a parallel appearance of irritation, sensitization, or other adverse reactions. Based on these available data, it was concluded that Biotin is safe as used in cosmetic formulations.