Beauty fad’s ugly downside: test interference

September 2016—It’s the kind of health promotion advice one might pick up casually over lunch with friends, in a quick Google search, or during a visit to the hairdresser. Take megadoses of an over-the-counter vitamin called biotin—a common supplement in multivitamin compounds—and watch your skin improve and your hair and nails thicken and gleam. In recent years, online social networks and health-related websites have begun to teem with ads claiming that people have seen a transformation since they jumped on the biotin bandwagon.