“There is a theory that biotin supplements may interfere with the absorption of vitamin B5 (pantothenic acid) because they use the same pathway. Pantothenic acid is thought to be important for the normal functioning of the epidermis, or top layer of the skin, so having less of it can potentially cause acne,” Lin explains.

However, not everyone gets rashes caused by biotin. “Based on the possible mechanism of action, it can happen to anyone, but those who are more prone to acne may be more susceptible,” explains board-certified dermatologist Marisa Harszyk, MD, FAAD.

Bottom line: “Anyone with acne should be extremely careful with high-dose biotin,” Gronic notes. And if you love biotin for its beauty benefits (many do!), you might want to make sure you’re getting enough pantothenic acid in the mix. Next: How to shop smart.