Until recently, one of the most popular cosmetic raw materials, especially among washing cosmetics, was Sodium Lauryl Sulfate (SLS) – a sodium salt of lauryl sulfate. This material, however, was characterized by a significant degree of skin irritation, a relatively low aqueous solubility and limited possibilities to thicken the cosmetic formulation. Today, SLS has been mostly replaced by its ethoxylated derivative - Sodium Laureth Sulfate (SLES).

SLES has a lower degree of skin irritation, ease of compaction and insensitivity to hard water. It also has very good properties, is inexpensive and readily available and therefore readily used by the manufacturers. On the other hand, it shows a high affinity for proteins of the stratum corneum and by eluting lipids from the surface of the epidermis it leads to disorganization of its liquid crystal structure. This results in an important increase in Trans-Epidermal Water Loss (TEWL) and damage to the barrier function of the skin. For this reason, more and more conscious consumer draws attention to the presence of SLES used in their cosmetic products.

The irritant potential of SLES was subjected to numerous tests. However, the results are often very different, and making their interpretation one should keep in mind that the name of the raw "Sodium laureth sulfate" does not describe one single compound, but a mixture of sulfate derivatives of aliphatic alcohols with different hydrocarbon chains. Molecular formula of this material is: R- (OCH2CH2) n-OSO3-Na+ wherein R is an alkyl chain with a length varying from 10 to 18 carbon atoms (mainly twelve C atoms, 12), and an average degree of ethoxylation, n, of 2-3. Depending on the producer of the raw material, the structure of the SLES can vary considerably, hence resulting in differences in the irritating potential of this surfactant.

To exclude the SLES from their formulation descriptions, cosmetics manufacturers often decide to use its close derivatives. But such a solution is not without drawbacks. Most SLES derivatives have a similar, sometimes even greater irritant potential. Some cosmetic manufacturers go as far as to label their cosmetics "SLES-free", despite the fact that the composition of the formulation still contains very similar molecule that differ slightly in length carbon chains or the accompanying cation (eg. Lithium or ammonium salts instead of sodium salts).