Researchers found 18 cases where biotin helped hair and nail growth—but every single person had an underlying deficiency or condition causing the problem in the first place. For healthy people with normal biotin levels, there's basically no evidence that biotin supplements actually work. The bottom line: biotin only seems to help if something's actually wrong.

Researchers searched PubMed for all published studies and case reports about biotin and hair or nail growth. They reviewed everything they found to see what the evidence actually showed.

Funding not disclosed in abstract