SLS and SLES play similar roles in home cleaners and cosmetics. You can often find both of these surfactants or foaming agents in dish soap, liquid laundry detergents, toilet-bowl cleaners, shampoos, bubble bath and facial cleaners. Both can be derived from petroleum, although there are plant-based alternatives as well.
SLS is a skin, eye and respiratory tract irritant that Environment Canada has also categorized as inherently toxic to aquatic organisms, flagging it for further assessment.
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To make SLS less irritating, it is often ethoxylated (by adding ethylene oxide), resulting in the modified compound of SLES. But SLES is also a concern because it can be contaminated with 1,4-dioxane, which may cause cancer (according to the International Agency for Research on Cancer), and it stays in the environment for a long time. Contamination occurs during the process of ethoxylation.
Adria Vasil, author of Ecoholic Home, notes that even some organic dish soaps contain troubling levels of 1,4-dioxane. The good news is that many brands—from Seventh Generation to Whole Food's 365 to Ecover had only trace amounts or have reformulated their products.