Side by side
| SLS (sodium lauryl sulfate) | SLES (sodium laureth sulfate) | |
|---|---|---|
| What it is | Sulfated fatty alcohol | SLS with added ethylene oxide units (ethoxylated) |
| Cleaning and foam | Very strong, dense foam | Strong, slightly softer foam |
| Skin irritation | High — used as the standard irritant in dermatology tests | Moderate — noticeably gentler |
| Eye irritation | High | Lower |
| Allergy | Very rare (irritant, not allergen) | Very rare |
| 1,4-dioxane risk | None | Possible trace contamination; regulated |
| Cancer risk | No | No (dioxane is the contaminant concern, not SLES) |
| Typical use | Toothpaste, some body wash, dish soap, industrial cleaners | Shampoo, body wash, hand soap, bubble bath |
| Cost | Lowest | Low |
| Mouth ulcers (toothpaste) | Associated in some studies | Rarely used in toothpaste |
Why SLES is gentler
Ethoxylation adds a chain of ethylene oxide units to the SLS molecule, which makes it larger and less able to penetrate and disrupt the skin barrier. In clinical irritation testing SLES consistently produces less redness, dryness, and barrier damage than SLS at the same concentration, while cleaning nearly as well. This is why the shampoo aisle moved to SLES decades ago and why 'contains SLES' is not a reason to reject a product.
The 1,4-dioxane question
Ethoxylation is done with ethylene oxide, and a side reaction produces 1,4-dioxane, which is classified as a probable human carcinogen. It's not an ingredient — it's a manufacturing by-product — so it never appears on a label. Manufacturers remove it by vacuum stripping, and the FDA has monitored levels since the 1970s; typical modern products contain a few parts per million or less. New York State set a legal limit of 1 ppm in personal-care products from 2023, which pushed the industry lower. The EU treats it as a prohibited substance in cosmetics with trace levels tolerated only where technically unavoidable.
For consumers, the practical implication is small: choose established brands, and if you want to avoid the question entirely, choose SLS (which isn't ethoxylated) or a sulfate-free cleanser. It's not a reason to prefer SLS on skin, where SLES's gentleness matters more.
Which to choose
- Normal skin and scalp, oily hair — either works; SLES is the default in most products anyway
- Dry or sensitive skin, eczema, itchy scalp — SLES over SLS, and sulfate-free (glucosides, sarcosinates, isethionates) if SLES still irritates
- Toothpaste with recurring mouth ulcers — look for SLS-free formulas
- Colour-treated or very dry hair — sulfate-free, or at least SLES
- Babies and children — SLES-based or sulfate-free 'tear-free' cleansers; SLS is too harsh
- Frequent hand-washing — SLES or glucoside-based hand soap; SLS dries hands out fastest
What both do and don't do
Neither causes cancer, hormone disruption, or hair loss. Both are biodegradable. Both can strip natural oils if used too often or left on skin. Both are 'derived from coconut', which is true and says nothing about how they behave. The meaningful difference is irritation, and the meaningful decision is whether you need a sulfate at all — for most cleaning jobs on skin you don't, but sulfate cleansers remain the cheapest, most effective way to remove heavy oil and styling product.
Is it in your product?
Paste the ingredient list or snap a photo of the label — IngredientIQ rates every ingredient in seconds.
Common questions
Is SLES safer than SLS?
Gentler, yes — measurably less irritating to skin and eyes. 'Safer' in the sense of long-term health, they're equivalent; neither is a carcinogen or hormone disruptor. SLES has the 1,4-dioxane manufacturing issue, which regulated brands control.
Does SLES cause cancer?
No. The concern is trace 1,4-dioxane contamination from manufacturing, which is regulated and stripped to very low levels by reputable producers. SLES itself has no carcinogenic activity.
Why do toothpastes use SLS instead of SLES?
SLS foams better in the mouth, has mild antibacterial action, and SLES's ethoxylation isn't wanted in a product that's partly swallowed. If SLS gives you mouth ulcers, SLS-free toothpastes are widely available.
Is 'sulfate-free' always better?
Not always. Sulfate-free cleansers are gentler but clean less aggressively, which can leave oily scalps and heavy product build-up. Some sulfate-free surfactants (cocamidopropyl betaine) are more allergenic than SLES. Choose by your skin, not by the label claim.
Related
Sources
- Cosmetic Ingredient Review, Safety Assessment of Sodium Lauryl Sulfate, Sodium Laureth Sulfate, and related ingredients
- US FDA, 1,4-Dioxane in Cosmetics: A Manufacturing Byproduct
- New York State Environmental Conservation Law §37-0117 (1,4-dioxane limits)
- Löffler & Happle, Profile of irritant patch testing with detergents: SLS, SLES and alkyl polyglucoside, Contact Dermatitis, 2003