Researchers found 18 cases where biotin helped with hair and nail growth—but only in people who had an underlying deficiency or condition. For healthy people with normal biotin levels, there's basically no solid evidence that biotin supplements actually work. The bottom line: biotin might help if something's actually wrong, but it's probably not worth taking if your hair and nails are already fine.

Researchers searched medical databases for all published studies and case reports about biotin and hair/nail growth, then reviewed what they found to see if the evidence actually supported the hype.

Funding not disclosed in abstract