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.
Related
How to spot SLS, SLES & 1,4-dioxane on a label
SLS, SLES & 1,4-dioxane rarely appears under that exact name on packaging. Manufacturers use trade names, umbrella terms such as "fragrance" or "performance finish", or simply omit process chemicals that are not classed as intentional ingredients. That is why reading a claim ("free from", "non-toxic", "natural") tells you far less than reading the composition and the certifications behind it.
The practical approach is to work backwards from certifications that test finished products rather than from ingredient lists alone. A scheme with residue limits and third-party lab testing catches substances that a marketing claim will never mention, including contamination introduced during dyeing, coating or packaging.
Exposure also depends on use. The same substance matters much more in something worn against skin all day, heated, chewed, or used on broken skin than in a rigid object handled briefly. Judge risk by contact, duration and temperature, not by the scariness of the name.
Claim vs. verification
| What you see | What it proves | What to do |
|---|---|---|
| “Free from” on the front of pack | Nothing verifiable on its own — unregulated wording | Look for a named standard or test method |
| Full ingredient or fibre list | Intentional inputs only, not process residues | Cross-check against a residue-tested certification |
| Third-party certification | Audited limits, usually with lab testing | Confirm scope, product line and expiry date |
| Published test report | Strongest evidence available | Check the lab, the date and the method used |
Safer-swap checklist
- Prefer residue-tested schemesOEKO-TEX, GOTS and equivalents set limits and test finished goods.
- Cut the coatingsStain-, water- and wrinkle-resistant finishes are the most common carriers of unwanted chemistry.
- Mind the heatHeat and abrasion increase migration; choose plainer materials for anything hot or worn.
- Ask for the certificateA brand that holds one will send the number; a brand that does not will change the subject.