1,4-Dioxane (PEG or Sodium Laureth Sulfate)
Commonly found in: bubble bath, shampoo, liquid soap, and hair relaxers.
Why you should avoid it: "1,4-dioxane is classified as a probable human carcinogen according to the International Agency on Research for Cancer," Harper told us. "But you won't find it on any ingredient list because this chemical is the byproduct of the process that is used to make certain types of surfactants, such as sodium laureth sulfate, and is considered an incidental ingredient not requiring ingredient disclosure."
Products without 1,4-dioxane to try instead: