Sodium Laureth 8 sulfate, (SLES) is an anionic detergent used in cosmetics and, as for all SLES, rather discussed.

The number appearing after Sodium Laureth represents the molecular weight and the higher this number is, the less it penetrates the skin.

Sodium Laureth sulfate or SLES, is a chemical compound and belongs to a group of salts of sulfated ethoxylated alcohols. 

The name describes the structure of the molecule:

• Sodium indicates the presence of sodium ions in the molecule, which are responsible for the compound's solubility in water.
• Laureth is a term derived from the word "lauryl ether". "Laureth" indicates that the original lauryl alcohol molecule has been treated with ethylene oxide.
• 8 indicates the average number of ethylene oxide units in the chain. These units make the compound more water-soluble and less irritating to the skin compared to sodium lauryl sulfate.
• Sulfate. This part of the molecule is responsible for the compound's cleansing and foaming properties.

Raw Materials Used in Production.

• Fatty Alcohols are derived from vegetable or petrochemical sources and serve as precursors.
• Ethylene oxide is a chemical compound used to produce polyethers.
• Sulfuric acid is used to sulfate the ethoxylated fatty alcohols.

Step-by-step Summary of Industrial Production Process.

• Ethoxylation of Fatty Alcohols. Fatty alcohols are made to react with ethylene oxide to produce ethoxylated fatty alcohols.
• Sulfation. The ethoxylated fatty alcohols are then sulfated using sulfuric acid.
• Neutralization. The mixture is neutralized with sodium hydroxide to produce Sodium Laureth 8 Sulfate.
• Purification. The resulting product is purified to remove impurities and by-products.

Sodium Laureth 8 sulfate occurs in liquid form or clear transparent slightly yellow gel or white fine powder.

SLES (Sodium laureth sulfate) must not be confused with SLS (Sodium laureth sulfate) because, although both are similar and have sulphuric acid and lauryl alcohol as their formula, in SLES, which is less aggressive than SLS but is ethoxylated (obtained from ethylene oxide), it is not uncommon to find in SLES ethylene oxide and 1,4-dioxane residues, chemical compounds that are considered carcinogenic.

A preliminary remark must be made about synthetic surfactants, which can be divided into four groups:

• Anionic (SLS, ALS, SLES), which solubilises well with lipid monolayers but not with lipid bilayers model of liposomes or cytotoxicity tests towards cultured skin cells
• Nonionic amphoteric (CAPB), which solubilises well with both mono- and bilayers
• Biotensioactive (SAP), which penetrates monolayers at 1% dry mass without solubilisation, and probably penetrates bilayers, increasing their size (without solubilisation).

Cosmetics

INCI Functions:

Cleansing agent. Ingredient that cleanses skin without exploiting the surface-active properties that produce a lowering of the surface tension of the stratum corneum. 

Foaming.  Its function is to introduce gas bubbles into the water for a purely aesthetic factor, which does not affect the cleaning process, but only satisfies the commercial aspect of the detergent by helping to spread the detergent. This helps in the commercial success of a cleansing formulation. Since sebum has an inhibiting action on the bubble, more foam is produced in the second shampoo. In practice, it creates many small bubbles of air or other gases within a small volume of liquid, changing the surface tension of the liquid.

Surfactant - Cleansing agent. Cosmetic products used to cleanse the skin utilise the surface-active action that produces a lowering of the surface tension of the stratum corneum, facilitating the removal of dirt and impurities. 

The most relevant studies on this chemical compound have been selected with a summary of their contents:

Sodium laureth sulfate safety

Typical characteristics of the commercial product Sodium lauryl polyoxyethylene ether sulfate Sodium Laureth Sulfate (SLES) 

• Molecular Formula: C₁₄H₂₉NaO₅S
• Molecular Weight: 332.431 g/mol
• CAS: 9004-82-4  15826-16-1
• EC Number: 239-925-1  618-398-5
• UNII 410Q7WN1BX
• DSSTox Substance ID: DTXSID2029298    DTXSID70274019
• MDL number  
• PubChem Substance ID 
• InChI=1S/C14H30O5S.Na/c1-2-3-4-5-6-7-8-9-10-11-12-18-13-14-19-20(15,16)17;/h2-14H2,1H3,(H,15,16,17);/q;+1/p-1  
• InChl Key      ASEFUFIKYOCPIJ-UHFFFAOYSA-M
• SMILES    CCCCCCCCCCCCOCCOS(=O)(=O)[O-].[Na+]
• IUPAC   sodium;2-dodecoxyethyl sulfate
• ChEBI

Synonyms:

• SLES
• Sodium dodecylpoly(oxyethylene) sulfate
• Sodium Alkyl Ether Sulfate
• Sodium laureth-5 sulfate
• Sodium laureth-8 sulfate
• Sodium dodeceth-1 sulfate
• Dodecyl sodium ethoxysulfate
• Sodium lauryl oxyethyl sulfate
• Sodium lauryl polyoxyethylene ether sulfate
• Sodium 2-(lauryloxy)ethyl sulfate
• Sodium 2-(dodecyloxy)ethyl sulfate
• Ethanol, 2-(dodecyloxy)-, hydrogen sulfate, sodium salt
• 2-(Dodecyloxy)ethyl sodium sulfate
• Etoxon EPA
• Sodium lauryl ethoxysulphate
• Sodium lauryl sulfate ethoxylate
• Sodium laureth-12 sulfate
• PEG-5 Lauryl ether sulfate, sodium salt
• PEG-7 Lauryl ether sulfate, sodium salt
• PEG-8 Lauryl ether sulfate, sodium salt
• PEG-12 Lauryl ether sulfate, sodium salt
• Sodium polyethylene glycol (7) lauryl ether sulfate
• Sodium polyethylene glycol 600 lauryl ether sulfate
• Polyoxyethylene (5) lauryl ether sulfate, sodium salt
• Polyoxyethylene (7) lauryl ether sulfate, sodium salt
• Polyoxyethylene (8) lauryl ether sulfate, sodium salt
• Polyoxyethylene (12) lauryl ether sulfate, sodium salt
• Polyethylene glycol (5) lauryl ether sulfate, sodium salt
• Polyethylene glycol 400 lauryl ether sulfate, sodium salt
• Polyethylene glycol 600 lauryl ether sulfate, sodium salt
• Dodecanol, ethoxylated, monoether with sulfuric acid, sodium salt
• Sodium laureth-3 sulfate
• Sodium laurylpoly(oxyethylene) sulfate
• Sodium polyoxyethylene (8) sulfate
• alpha-Sulfo-omega-(dodecyloxy)poly(oxy-1,2-ethanediyl) sodium salt
• Poly(oxy-1,2-ethanediyl), alpha-sulfo-omega-(dodecyloxy)-, sodium salt
• Glycols, polyethylene, mono(hydrogen sulfate), dodecyl ether, sodium salt
• Sodium polyoxyethylene (5) lauryl ether sulfate
• Sodium polyoxyethylene (7) lauryl ether sulfate
• Sodium polyoxyethylene (12) lauryl ether sulfate
• Sodium polyethylene glycol (5) lauryl ether sulfate
• 2-(Dodecyloxy)ethanol hydrogen sulfate sodium salt
• Laureth-8 carboxylic acid, sodium salt
• Polyethylene glycol sulfate monododecyl ether sodium salt
• Sodium polyethylene glycol 400 sulfate
• Polyethylene glycol (7) lauryl ether sulfate, sodium salt
• Sodium (lauryloxypolyethoxy)ethyl sulfate
• Sodium poly(oxyethylene) lauryl ether sulfate
• 15826-16-1
• Standapol ES 2
• Sodium 2-(dodecyloxy)ethyl sulphate
• Sodium laureth-7 sulfate

 References______________________________________________________________________

(1) Vleugels LF, Pollet J, Tuinier R. Polycation-sodium lauryl ether sulfate-type surfactant complexes: influence of ethylene oxide length. J Phys Chem B. 2015 May 21;119(20):6338-47. doi: 10.1021/acs.jpcb.5b02043.

(2) Black RE, Hurley FJ, Havery DC. Occurrence of 1,4-dioxane in cosmetic raw materials and finished cosmetic products. J AOAC Int. 2001 May-Jun;84(3):666-70.

(3) Ethylene oxide. IARC Monogr Eval Carcinog Risks Hum. 1994;60:73-159. 

(4) 1,4-Dioxane. IARC Monogr Eval Carcinog Risks Hum. 1999;71 Pt 2(PT 2):589-602.

Wilbur S, Jones D, Risher JF, Crawford J, Tencza B, Llados F, Diamond GL, Citra M, Osier MR, Lockwood LO. Toxicological Profile for 1,4-Dioxane. Atlanta (GA): Agency for Toxic Substances and Disease Registry (US); 2012 Apr.

(5) Scaratti G, De Noni Júnior A, José HJ, de Fatima Peralta Muniz Moreira R. 1,4-Dioxane removal from water and membrane fouling elimination using CuO-coated ceramic membrane coupled with ozone. Environ Sci Pollut Res Int. 2020 Jun;27(18):22144-22154. doi: 10.1007/s11356-019-07497-6.