In the world of beauty supplements, biotin is treated as the magic fix—like the beauty equivalent of restarting your phone. Hair feeling thin? Take biotin! Brittle nails? Try biotin! Skin looking blah? B-I-O-T-I-N. You hear about it so often that you probably don’t even think to question it.

But if you’ve long been taking biotin for hair benefits and have noticed absolutely zero difference in how long or thick it is, you might be wondering if it’s just a capsule full of lies. So, [Cosmopolitan] turned to board-certified dermatologist Dhaval G. Bhanusali, MD, and trichologist Bridgette Hill with Paul Labrecque Salon and Skincare Spa for the facts.