1,4-dioxane

Carcinogenic. Readily penetrates the skin. Products most likely to be contaminated with 1,4-dioxane are those with PEG, polyethylene, polyethylene glycol, polyoxyethylene, "eth" (e.g., sodium laureth sulfate), or oxynol in the ingredients. Polysorbate 60 and polysorbate 80 may also be contaminated.