Sodium Cocoyl Isethionate (SCI) is an anionic surfactant obtained by esterifying coconut fatty acids with sodium isethionate (sodium 2-hydroxyethanesulfonate). Its sulfonate head group, linked to the fatty chain through an ester bond, gives it cleansing power close to that of sulfates with markedly lower aggressiveness towards keratin and the skin barrier. Together with amino acid surfactants such as Sodium Lauroyl Sarcosinate and Sodium Cocoyl Glutamate, it forms the family of mild cleansers that now underpins professional sulfate-free shampoos.

These molecules are not simply “green” substitutes for Sodium Lauryl Sulfate (SLS). Their mildness has a chemical explanation: the size of the head group, the type of bond between fatty chain and ionic group, and their behaviour in the presence of calcium and magnesium. Hairswiss explains what sets them apart and how to read them in an INCI list.

What is Sodium Cocoyl Isethionate?

SCI is a mixture of isethionate esters whose fatty chain comes from coconut oil, mainly C12 (lauric acid) with C8 to C18 fractions. Its main component, Sodium Lauroyl Isethionate, has the formula C14H27NaO5S and a molar mass of about 330 g/mol. Industrially it is made by direct esterification of the fatty acids with sodium isethionate at high temperature, yielding a white solid supplied as powder, flakes or needles.

Its structure combines two elements:

• a sulfonate group (–SO3⁻), strongly ionised across the whole cosmetic pH range, which solubilises soil;
• an ester bond between the fatty chain and the head group, which lengthens and hydrates the hydrophilic part and reduces penetration of the surfactant into protein layers.

The ester bond sets a formulation limit: it hydrolyses in strongly acidic or alkaline conditions. SCI is therefore formulated close to neutral, typically between pH 5 and 8, which suits shampoos for coloured and sensitised hair.

What are amino acid surfactants?

Amino acid surfactants are N-acyl amino acids: a fatty chain is attached through an amide bond to the nitrogen of an amino acid, whose carboxylate group becomes the anionic head. The two most used in hairdressing are:

• Sodium Lauroyl Sarcosinate, derived from sarcosine (N-methylglycine), with the formula C15H28NNaO3 and a molar mass of about 293 g/mol;
• Sodium Cocoyl Glutamate, derived from L-glutamic acid, which carries two carboxylic groups and a bulkier head group.

The amide bond is far more resistant to hydrolysis than the ester bond of SCI. The carboxylate head, however, is weakly acidic: at low pH part of the molecules become protonated, less soluble and less foaming. These surfactants perform best between pH 5.5 and 7 and are rarely used alone as the primary surfactant.

Why are these surfactants milder than sulfates?

The irritation a surfactant causes depends largely on how strongly it binds to proteins and denatures them. SLS, with the formula C12H25NaO4S (about 288 g/mol) and a critical micelle concentration close to 8 mmol/L at 25 °C, has a small, highly charged sulfate head: its free monomers readily penetrate the stratum corneum and the cuticle, where they bind to keratin and extract lipids.

The zein test, based on a water-insoluble corn protein, measures this aggressiveness: the more zein a surfactant dissolves, the more it denatures proteins. SCI, sarcosinates and glutamates dissolve markedly less zein than SLS. Their bulkier head group forms more stable micelles, lowering the concentration of free monomers able to attack the fibre.

On hair, this means:

• gentler extraction of surface lipids, including the 18-MEA layer that keeps the cuticle hydrophobic;
• less cuticle swelling during washing;
• reduced pigment loss on coloured hair, linked to less lifting of the scales.

How do they behave in hard water?

Switzerland has many areas with hard water, rich in calcium and magnesium. Traditional soaps (fatty acid carboxylates) precipitate there as insoluble lime soaps that dull the hair. Thanks to its sulfonate head, SCI tolerates divalent ions well and is an effective lime soap dispersant: it limits deposits even in calcareous water.

Sarcosinates and glutamates, despite their carboxylate head, remain far more tolerant than soaps because the amide bond and the amino acid chain change the geometry of the head group. This is one reason they are often combined with SCI and amphoteric surfactants (betaines, sultaines) in professional formulas.

What are the trade-offs for professionals?

Mild cleansers do not replace sulfates without compromise. As our analysis of sulfate-free formulations explains, three limits need to be considered:

• Viscosity: SCI and sarcosinates do not thicken with salt like SLES; formulators rely on polymers or fatty esters, so the texture is sometimes thinner or pearlescent.
• Foam: creamier and finer, but less voluminous on the first wash of hair heavily loaded with styling products.
• Cleansing power: sufficient for daily washing, more limited against heavy silicones and film-forming resins; an occasional clarifying shampoo remains useful.

In practice, most professional shampoos combine several surfactants: a primary surfactant (sulfosuccinate, olefin sulfonate or SCI), an amino acid co-surfactant and an amphoteric. This synergy lowers the overall irritation of the blend, because the mild surfactants insert into the micelles of the primary surfactant and reduce the amount of free monomers. Sodium C14-16 Olefin Sulfonate is often the base of these mixed systems.

Which professional shampoos use these surfactants?

Nika Frozen Blonde Shampoo, available on cliCHair.ch, is a good example of a multi-cleanser mild system: it combines Sodium Cocoyl Isethionate, Sodium Lauroyl Sarcosinate and Coco-Glucoside with Disodium Laureth Sulfosuccinate, with no sulfate in the INCI list. On bleached hair, this base limits lipid extraction and gives the Acid Violet 43 pigment time to settle on the fibre and neutralise yellow tones.

Liss Komplex Hydra Shampoo by Edelstein, which Swiss professionals find on cliCHair.ch, uses Sodium Lauroyl Sarcosinate and Coco-Glucoside together with Sodium C14-16 Olefin Sulfonate, complemented by hydrolysed keratin and silk: an example of a mixed system in which mild surfactants temper the primary surfactant.

How can you recognise these surfactants in an INCI list?

• Isethionates: Sodium Cocoyl Isethionate, Sodium Lauroyl Methyl Isethionate. Free Sodium Isethionate at the end of the list is normal: it is a synthesis residue.
• Sarcosinates: Sodium Lauroyl Sarcosinate, Sodium Cocoyl Sarcosinate.
• Glutamates and other amino acids: Sodium Cocoyl Glutamate, Disodium Cocoyl Glutamate, Sodium Cocoyl Glycinate, Sodium Methyl Cocoyl Taurate.

Position in the list remains decisive: a glutamate listed after the fragrance, behind a Sodium Laureth Sulfate at the top, does not make a shampoo a mild cleanser. The primary surfactant sets the profile of the formula.

Conclusion

Sodium Cocoyl Isethionate and amino acid surfactants owe their mildness to their molecular architecture: a bulky head group, an ester or amide bond between fatty chain and ionic group, and a low tendency to denature keratin. For hairdressers they are the logical base for washing coloured, bleached or sensitised hair, provided they are read in the context of the whole formula and a clarifying shampoo is planned when deposits build up.