Biotin

Biotin (vitamin B7) is typically used at low concentrations in topical “hair/skin/nail” products and functions as a supportive vitamin rather than an exfoliating or barrier-disrupting active. Clinical experience and patch-testing literature suggest it is generally well tolerated, with irritation or allergy being uncommon but possible in highly reactive individuals or when combined with other irritants in a formula. Given the need to account for sensitized/eczema-prone patients while recognizing its low inherent reactivity, it fits a very gentle profile. Safety Notes: In mass-market shampoos/conditioners, biotin is often included at very low “label claim” levels (commonly in the ~0.00001–0.01% range) primarily for marketing and because it is typically part of broader vitamin blends. Higher-strength OTC scalp serums, hair tonics, and leave-on treatments marketed for strengthening/thickening can reach ~0.1–0.5% biotin, with 0.5% representing the upper end seen in consumer-available products due to solubility, cost, and diminishing formulation practicality. Biotin appears in both rinse-off and leave-on products, with the highest levels more often found in leave-on scalp/hair treatments rather than rinse-off formats.