Sodium laureth sulfate is on the Red List from Campaign for Safe Cosmetics, a project of Breast Cancer Prevention Partners (previously the Breast Cancer Fund). From manufacture, SLES may be contaminated with the toxic substances ethylene oxide and 1,4- dioxane.
To make sodium lauryl sulfate (SLS) less irritating, ethylene oxide is added (ethoxylation), writes the David Suzuki Foundation. Sodium lauryl sulfate (SLS) then becomes sodium laureth sulfate (SLES). But another issue occurs instead because during the ethoxylation, contamination from 1,4-dioxane could occur. Even organic dish soaps have been found to have contamination from 1,4.dioxane.
It is likely that this substance is derived from palm oil.
Even though it is not listed on the ingredient labels, products with sodium laureth sulfate may also contain impurities from: