Biotin
Biotin, also known as Vitamin H, is a water-soluble B-vitamin and the main component of many enzymes in the body. Its CAS number is 58-85-5 and it is officially listed in CosIng with functions including antiseborrhoeic, hair conditioning, and skin conditioning. It is commonly used in hair and nail supplements as well as topical cosmetic formulations.
Biotin is well-established as an oral supplement for supporting stronger nails and hair. When applied topically, manufacturer claims suggest it can smooth the skin and strengthen hair, though the source notes these effects are more questionable outside of supplementation.
Topical efficacy is uncertain according to the source; benefits are more supported for oral supplementation than for cosmetic application.
