Sodium laureth sulfate

What it is

Sodium laureth sulfate (SLES) is lauryl alcohol that has been ethoxylated (typically 1-3 ethylene-oxide units, written SLE1S, SLE2S, SLE3S) and then sulfated. It belongs to the salts of sulfated ethoxylated alcohols reviewed by the Cosmetic Ingredient Review (CIR) (Robinson 2010). Sulfate surfactants such as SLS and SLES are the most common primary surfactants in shampoo and remain unmatched for performance at low cost (Thompson 2023).

How it works

• It cleans by the same anionic mechanisms as SLS (see how shampoo works).
• Why it is milder than SLS: added ethoxylate groups increase skin mildness, though they also make the formula harder to thicken because worm-like micelles form less readily (Thompson 2023).
• In most shampoos it is paired with an amphoteric co-surfactant such as cocamidopropyl betaine, which further lowers irritation (Thompson 2023; Morris 2021).
• Procter & Gamble has used SLE1S as the anionic partner in a fatty-alcohol gel-network shampoo that delivered cetyl and stearyl alcohol into hair in vitro (Marsh 2017).

What the studies show

• A CIR amended safety assessment found SLES and ammonium laureth sulfate caused no adverse responses in toxicology testing other than irritation. They are dermal and eye irritants but not sensitizers, and are safe when formulated to be non-irritating (Robinson 2010).
• Cell assays and 24-hour human patch tests of SLES and alternative blends ranked mildness in opposite orders for some blends (Chen 2026).
• In vitro, 15 anionic systems on human skin showed penetration tracked the micelle threshold and zeta potential, not micelle size (Morris 2019).
• US FDA data on 1,4-dioxane surveys show average levels in cosmetics fell from 50 ppm in 1981 to 19 ppm in 1997. In 2008 about 80% of products had none detected (limit 1 ppm) and the maximum was 11.6 ppm (FDA).

How it's used in studies

SLES is the primary surfactant in shampoos at up to about 10%, combined with 1-5% of an amphoteric co-surfactant (Thompson 2023).

Side effects and safety

• Irritation is possible and depends on concentration. It is generally lower than SLS and reduced further in blends. It is not a sensitizer (Robinson 2010).
• 1,4-dioxane is a by-product of ethoxylation, not an ingredient. The US FDA notes the National Toxicology Program considers it reasonably anticipated to be a human carcinogen, that the EU's scientific committee considers trace levels of 10 ppm or less safe, and that levels have fallen sharply since the 1980s because of vacuum stripping. FDA has set no federal limit. New York State caps personal care products, including shampoo, at 1 ppm from the end of 2023. Ingredients with "-eth-", "PEG" or "polyoxyethylene" in the name can carry it (FDA).
• It is a permitted cosmetic ingredient without a specific concentration cap in the US, EU and UK.

Bottom line

SLES is a reasonable default cleanser for most scalps, especially oily or product-heavy ones, and it is the base of most budget shampoos. It is gentler than SLS, and much of the "sulfates are harsh" reputation comes from SLS-heavy formulas or from people with sensitive skin. People with eczema-prone or very sensitive scalps, dry curly or coily hair, or freshly coloured hair may prefer milder primaries such as isethionates or amino-acid surfactants. The 1,4-dioxane concern is real but small at current levels. We are fairly sure of the irritation and safety profile, but no trial has tested hair outcomes: none shows SLES shampoos cause more breakage, colour loss or hair loss than sulfate-free shampoos.