Sodium Laureth Sulfate
SLES · Sodium Lauryl Ether Sulfate
What it is
An anionic ethoxylated surfactant derived by ethoxylation of lauryl alcohol then sulfation. The ethoxylation process creates a 1,4-dioxane contamination risk as a manufacturing byproduct.
In this product: Primary cleansing and foaming surfactant.
Dose & route, what actually matters
Dermal and inhalation (steam during washing). 1,4-dioxane can penetrate human skin from certain preparations; it evaporates readily from rinse-off products, reducing but not eliminating exposure.
EUROPEAN UNION
SLES itself is not restricted in EU Cosmetics Regulation Annex II or III. 1,4-dioxane (the contaminant) is listed in Annex II (entry 403) of the EU Regulation as a prohibited cosmetic ingredient; technically unavoidable trace impurities are governed by Article 17. SCCS guidance: ≤10 ppm 1,4-dioxane in finished cosmetics considered safe. Germany opened a REACH call for evidence in 2023 proposing a 1 ppm limit.
UNITED STATES
Permitted. FDA identifies 1,4-dioxane as a contaminant of concern but has not set a binding product concentration limit for cosmetics. New York State set a 10 ppm limit for cosmetics effective December 31, 2022. No federal product limit as of 2026.
The evidence
IARC classified 1,4-dioxane as Group 2B ('possibly carcinogenic to humans') based on sufficient evidence in animals. EPA classifies it as 'likely to be carcinogenic to humans.'
regulatory · 1987 · source
California Prop 65 fact sheet advises consumers to check labels for ingredients whose names end with '-eth-' (e.g., Sodium Laureth Sulfate) as markers of potential 1,4-dioxane contamination.
regulatory · 2022 · source
California Prop 65: 1,4-dioxane is listed on California Prop 65 as a carcinogen. Products containing SLES and other '-eth-' ingredients may contain it as a byproduct that never appears on the label.
How to avoid it
Look for shampoos that avoid all '-eth-' and '-PEG-' ingredients, or brands that publish third-party 1,4-dioxane test results. 'Sulfate free' products based on sodium cocoyl isethionate or sodium lauroyl sarcosinate skip this pathway entirely.
Where it hides
Editorial analysis of publicly available regulatory and peer-reviewed sources. Not medical advice. We name our evidence and link it, including when an ingredient is fine.