Many skin-care products and other cosmetics claiming to be natural, organic, green or some combination thereof have come and gone on store shelves and websites without leaving much of a mark. But it wasn’t until products started calling themselves “clean” that a critical mass of customers started poring over ingredient lists with the diligence of parents checking their children’s hair for lice. The result has been a revolution that is reshaping the beauty industry.

But why has the clean label — for which there is no regulatory definition — so captured the public’s devotion? Why are dermatologists so disdainful of the concept? And what does it mean?