SLS, SLES & 1,4-dioxane
Powerful foaming surfactants — the real concern is the 1,4-dioxane contamination that ethoxylation creates.
Also listed as: sodium lauryl sulfate, sodium laureth sulfate, ethoxylated surfactants
What it is
SLS and SLES are anionic surfactants responsible for the lather in shampoo, toothpaste and washing-up liquid. SLES is made by ethoxylating SLS to reduce irritation, and that reaction can leave 1,4-dioxane behind as a by-product.
Why it's worth avoiding
SLS itself is a straightforward skin and eye irritant at higher concentrations. 1,4-dioxane is the more serious issue: it is a probable human carcinogen and is not required to appear on the ingredient list because it is a contaminant, not an ingredient.
What the evidence says
IARC classifies 1,4-dioxane as Group 2B (possibly carcinogenic to humans). New York State set a 1 ppm limit in personal-care products from 2023 after testing found higher levels in common shampoos and detergents.
How it's regulated
New York's limits (2 ppm household cleaning, 1 ppm personal care, tightening over time) are the strictest US rules. The EU requires manufacturers to keep 1,4-dioxane technically unavoidable and as low as possible.
Label clues
- Ingredients containing 'laureth', 'PEG-', '-eth-' or ending in '-oxynol'
- Very high foam claims in budget shampoos and detergents
- No statement about vacuum stripping or dioxane testing
Safer swaps
- Coco-glucoside, decyl glucoside, sodium coco-sulfate formulas
- Soap-based or syndet bars with short ingredient lists
- Brands publishing 1,4-dioxane test results or NY compliance
- Fluoride toothpastes without SLS if you get mouth ulcers
Where it shows up
Frequently asked
Is sulfate-free shampoo better?+
For coloured, curly or very dry hair, usually yes — milder glucoside surfactants strip less. For oily scalps, a sulfate wash used occasionally is perfectly reasonable.
Is SLS a carcinogen?+
No. SLS is an irritant, not a carcinogen. The carcinogenicity question relates to 1,4-dioxane, a contaminant of ethoxylated ingredients such as SLES.