Sodium Laureth Sulfate

Sodium laureth sulfate is a cleansing surfactant. It is not listed among prohibited or restricted substances in the annexes to Regulation (EC) No 1223/2009. It helps detach sebum and dirt from skin or hair and suspend them in water until rinsing. The European CosIng database lists four functions, including cleansing and foaming.

Two points deserve a closer look: the few letters separating two nearly identical names, and 1,4-dioxane.

How a surfactant works

A surfactant molecule has two parts that behave differently: one is attracted to water, the other to oils. In rinse water, it surrounds sebum and dirt particles and keeps them suspended until the water carries them away. This is the mechanism behind cleansing.

CosIng assigns this molecule four functions: cleansing, cleansing surfactant, foaming and emulsifying. Cleansing and foaming are separate entries because they are different properties of the same molecule.

Laureth and lauryl are different entries

The easiest misunderstanding lies at the end of a word. Sodium laureth sulfate and sodium lauryl sulfate have separate CosIng entries and descriptions. The first is the sodium salt of ethoxylated and sulfated lauryl alcohol; the second is the sodium salt of lauryl sulfate. Their CAS numbers and function lists differ, because CosIng also assigns sodium lauryl sulfate a denaturing function.

The three letters ‘eth’ indicate ethoxylation: ethylene oxide groups have been inserted between the fatty chain and the sulfate group. The result is a larger molecule.

This distinction matters when reading research. Sodium lauryl sulfate is used as a reference irritant in dermatological patch testing and has been part of the German DKG research group’s baseline series for twenty years. Irritation data from that research concern sodium lauryl sulfate; those findings cannot simply be applied to sodium laureth sulfate.

Another useful label distinction: CosIng lists six CAS numbers under sodium laureth sulfate. The name covers a family of molecules differing in their degree of ethoxylation, while the label shows only the common name. The ingredient list therefore says little about that degree.

Our sodium lauryl sulfate guide explains what CosIng says about the other molecule and why irritation tests use it as a reference.

1,4-dioxane and the rule on traces

Ethoxylation can leave a by-product, 1,4-dioxane. Opinion SCCS/1570/15 explains that it forms during the processing of certain ethoxylated ingredients. It is not used as a cosmetic ingredient.

It therefore does not appear on the ingredient label. Article 19 of the Regulation defines an ingredient as a substance intentionally used during manufacture and excludes impurities in raw materials from that list.

1,4-dioxane is listed in Annex II to Regulation (EC) No 1223/2009 among substances prohibited in cosmetics. Processing residues, however, have a specific rule. Article 17 allows the unintended presence of a small quantity of a prohibited substance arising from impurities, manufacture, storage or migration from packaging, where it is technically unavoidable despite good manufacturing practice and provided that its presence complies with Article 3.

The committee also assessed a specific trace level. In opinion SCCS/1570/15, adopted on 15 December 2015, the Scientific Committee on Consumer Safety concluded that a trace level of 1,4-dioxane of 10 ppm or less in the finished product is safe for consumers.

The route to that conclusion is informative. The international ICCR working group had proposed two stages: first 25 ppm, then 10 ppm. The European committee disagreed and called for the 10 ppm level to be applied directly, with a short transition. The opinion’s minority-opinions section is empty.

Where to find it on the label

It appears as Sodium Laureth Sulfate in cleansing products. Ingredient order matters: above 1%, ingredients follow descending order, while those below that threshold may appear in any order. A surfactant near the top of the list can therefore provide some information about its relative amount.

The usual distinction applies: an ingredient guide describes a molecule. How an individual’s skin responds is another question.

The 1% rule is explained in full in our guide to reading an INCI list. If you have a list in front of you, the INCI analyser explains it ingredient by ingredient.

Sources: CosIng, European Commission, Sodium Laureth Sulfate and Sodium Lauryl Sulfate entries. Opinion SCCS/1570/15 of 15 December 2015. Regulation (EC) No 1223/2009, Articles 17 and 19 and Annex II.