Supplements that claim to improve appearance have grown in popularity in the past decade. From 2011 to 2020, the percentage of Americans who reported taking a hair, skin and nail vitamin in the past month rose from 2.5% to 4.9%.

But experts warn about side effects and dangers. Skin, hair and nail supplements often contain much more biotin than the human body needs, for example, a research paper published in the Journal of the American Academy of Dermatology has found.