Sodium lauryl sulfate in skincare: SLS and SLES explained

What sodium lauryl sulfate and SLES are

Both are detergents: they lift oil and dirt, and they make foam. Sodium lauryl sulfate (SLS, sometimes written sodium lauryl sulphate) and sodium laureth sulfate (SLES) are close relatives, and both appear in shampoos, body washes and cleansers.

The difference that matters for skin is the “eth” in the second name. SLES has been chemically modified, and the modification is what makes it gentler.

Why SLS is used to irritate skin on purpose

SLS is the standard irritant in dermatology research. Studies use it in patch tests to measure how easily skin is irritated and how well the barrier works. In one dose-response study, 12 volunteers were patch tested with 0.12, 0.25, 0.50 and 1.00% SLS, and the skin reaction rose steadily with the dose.¹

The effect on the skin barrier is measurable. In a study that treated forearm skin with 5% SLS for four hours, water loss through the skin rose from about 6 to about 18 g/m²/h, and the skin became about three times more permeable to the test molecules applied the next day.² Those are test conditions, much stronger and longer than a rinse-off cleanser, so they show what SLS can do, not what your shampoo does.

What this means in real life: how long a cleanser stays on your skin and how much SLS it contains matter more than the name. A leave-on product or a strong cleanser on already dry, cracked or eczema-prone skin is a different situation from a shampoo rinsed after a minute.

How SLES differs

A head-to-head patch-test study compared SLS with SLES at concentrations from 0.125% to 2.0% and exposure times of 6 to 24 hours. It found a pronounced reaction to SLS and a far milder one to SLES. The irritation from SLES was clearly detectable only up to day 7, while SLS still showed raised water loss on day 10.³

So if a product lists SLES rather than SLS, expect it to be gentler on skin, though not free of irritation.

The 1,4-dioxane question

The worry about SLES is not irritation. It is 1,4-dioxane, a trace contaminant that can form when some ingredients are made. The FDA says it is not an intentional ingredient, and that names containing “-eth-”, such as the “laureth” in SLES, are a cue that an ingredient is of the kind that can carry it. The page does not mention SLS at all.⁴

On safety, the FDA page notes that a US toxicology programme found 1,4-dioxane “reasonably anticipated to be a human carcinogen” based on animal studies, and that the EU’s safety committee considered trace levels of 10 ppm or less safe for consumers. It adds that manufacturing changes have significantly reduced levels over time, and that the FDA has recommended vacuum stripping since the 1980s to remove it.⁴

Snifff’s summary above sets out how the EU and India differ: the EU requires manufacturers to minimise it, and India has no equivalent purity limit for SLES. In the Cosmetics Regulation, 1,4-dioxane is listed in Annex II as a prohibited substance, and Article 17 permits only a small quantity that is technically unavoidable in good manufacturing practice and does not make the product unsafe.⁵

SLS and SLES in pregnancy and breastfeeding

Read that sentence slowly. It says Snifff did not find evidence specific to pregnancy or breastfeeding. It does not say these ingredients were studied and found safe, and it does not say they were found unsafe.

Evidence on cosmetic products in pregnancy is limited overall, so ask your doctor or midwife about the specific product you use.⁶

What you will see on the label

Look for Sodium Lauryl Sulfate (or Sodium Lauryl Sulphate) and Sodium Laureth Sulfate. Snifff has an entry for each, and shows both as Low risk. For the rest of the formula, see what the score means and how to read the list.

If your skin is dry or reactive, the more useful question than “does it contain SLS?” is “how long does it stay on my skin?”. Preservatives are covered on the parabens and phenoxyethanol pages.

As Snifff shows it

Sodium lauryl sulfate

Sodium Lauryl Sulfate

Low risk

Pregnancy and nursing

We found no pregnancy- or lactation-specific evidence for this ingredient.

Sodium Laureth Sulfate

Low risk

Pregnancy and nursing

We found no pregnancy- or lactation-specific evidence for this ingredient.

Regulatory gap

The EU requires manufacturers to minimise 1,4-dioxane, a carcinogenic manufacturing by-product. India has no equivalent purity limit for SLES.

Wording as it appears in the extension, which can change between releases.