What Is Sodium Laureth Sulfate (SLES)?
In plain English: Sodium laureth sulfate (SLES) is a foaming, grease-cutting anionic surfactant found in shampoos, dish soaps and body washes. It's milder on skin than its cousin SLS, but the way it's made can leave behind a hidden contaminant: 1,4-dioxane.
Also listed as: SLES, sodium lauryl ether sulfate, PEG lauryl ether sulfate
The honest science
SLES is made by 'ethoxylating' lauryl alcohol — adding ethylene oxide to soften a harsher surfactant into a gentler one. The catch is that this same reaction can generate 1,4-dioxane, an unwanted byproduct that rides along in the finished ingredient. 12
1,4-dioxane is classified by the U.S. EPA as a likely human carcinogen, and because it's a contaminant rather than an added ingredient, it never appears on a label. 2 You can't spot it by reading the back of the bottle. EWG's analysis has flagged a meaningful share of personal-care and cleaning products as potentially containing it. 2
Here's the honest part: SLES itself is not the villain, and the contamination is preventable. Manufacturers can strip out most of the 1,4-dioxane with a step called vacuum stripping, and states like New York now cap allowable levels in cleaning and personal-care products. 1 SLES is considered acceptable for use by the FDA and EU when purified. So the real question isn't 'is SLES evil' — it's 'did this maker bother to purify it,' and most labels won't tell you.
Where you'll find it
- shampoo
- dish soap
- body wash
- bubble bath
- foaming hand soap
- laundry detergent
The safer-swap angle: The cleanest way around the 1,4-dioxane question is to skip ethoxylated surfactants entirely in favor of sugar-derived ones like decyl glucoside — no ethoxylation, no dioxane to strip out in the first place.
Frequently asked questions
Is SLES the same as SLS?
No. SLES (sodium laureth sulfate) is the ethoxylated, milder version; SLS (sodium lauryl sulfate) is harsher on skin. The ethoxylation that makes SLES gentler is also what can introduce 1,4-dioxane contamination.
Why isn't 1,4-dioxane listed on the label?
Because it's not an added ingredient — it's a trace byproduct left over from manufacturing. Labeling laws only require listed ingredients, so a contaminant like this stays invisible unless the maker tests and discloses it.
Is SLES safe?
SLES itself is regarded as acceptable by the FDA and EU, and it's milder than SLS. The concern is the 1,4-dioxane it can carry. Purified SLES has very low levels, but you usually can't tell from the label whether it was purified.
Sources
- SODIUM LAURETH SULFATE — EWG's Guide to Healthy Cleaning — Environmental Working Group
- Hidden Carcinogen Taints Tap Water, Consumer Products Nationwide — Environmental Working Group
Ingredient safety data changes as new research is published, and product formulas change over time. Always read the current label and check primary sources.
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