Sodium cocoyl isethionate (SCI) is a chemical compound, a gentle surfactant derived from the fatty acid of coconut oil and isethionic acid. It is widely used in personal care products such as shampoos, body washes, and facial cleansers, thanks to its ability to produce rich and creamy foam and its effective yet gentle cleansing properties on the skin.

The name describes the structure of the molecule:

• Sodium Indicates the presence of a sodium ion (Na+) in the compound.
• Cocoyl refers to a fatty acid radical derived from coconut oil.
• Isethionate is a sulphate group with two oxygen atoms bonded to a carbon atom, which in turn is bonded to a sodium ion. The prefix 'iso' indicates a specific configuration of the atoms in the molecule.

The synthesis process takes place in different steps:

• Extraction of fatty acids from coconut oil through a process called hydrolysis, in which the oil is broken down into its component fatty acids and glycerol.
• Production of isethionic acid. Isethionic acid is a key ingredient in production and can be produced through the reaction of sodium bisulphite and ethylene oxide.
• Reaction of fatty acids with isethionic acid. Coconut fatty acids are reacted with isethionic acid in a reaction known as esterification to form the cocoyl ester of isethionic acid.
• Neutralisation. The resulting product is neutralised with sodium hydroxide (NaOH) to form Sodium Cocoyl Isethionate.
• Drying and grinding. The final product is then dried and ground into a fine powder or according to the desired form.

It appears in the form of a white powder. 

What it is for and where

Sodium cocoyl isethionate (SCI) is a widely used surfactant ingredient in synthetic detergents or, as they are commonly called in English, syndet bars.

Cosmetics

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

Hair conditioning agent. A significant number of ingredients with specific and targeted purposes may co-exist in hair shampoo formulations: cleansers, conditioners, thickeners, matting agents, sequestering agents, fragrances, preservatives, special additives. However, the indispensable ingredients are the cleansers and conditioners as they are necessary and sufficient for hair cleansing and manageability. The others act as commercial and non-essential auxiliaries such as: appearance, fragrance, colouring, etc. Hair conditioning agents have the task of increasing shine, manageability and volume, and reducing static electricity, especially after treatments such as colouring, ironing, waving, drying and brushing. They are, in practice, dispersants that may contain cationic surfactants, thickeners, emollients, polymers. The typology of hair conditioning agents includes: intensive conditioners, instant conditioners, thickening conditioners, drying conditioners. They can perform their task generally accompanied by other different ingredients.

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. 

Safety

The question we ask ourselves when we encounter a chemical component is always the same: does it hurt our health?

Here are some scientific studies that clarify the doubts.

Sodium cocoyl isethionate (SCI) is an important surfactant ingredient in mild, syndet (synthetic detergent) cleansing bars. In vitro and in vivo studies have demonstrated that SCI is mild and less damaging to the skin barrier than soaps and surfactants such as sodium dodecyl sulfate (SDS). We have recently shown that SDS forms small micelles in aqueous solutions contacting the skin relative to the aqueous pores in the stratum corneum (SC), and as a result, the SDS micelles can contribute to SDS skin penetration and induce skin barrier perturbation. In this paper, we attempt to explain the well-documented skin mildness of SCI by examining the size of the SCI micelles relative to that of the aqueous pores in the SC. For this purpose, we have conducted in vitro mannitol skin permeability and average skin electrical resistivity measurements upon exposure of the skin to an aqueous SCI contacting solution in the context of a hindered-transport aqueous porous pathway model of the SC. These in vitro studies demonstrate that an SCI micelle of radius 33.5 +/- 1 Angstrom (as determined using dynamic light-scattering measurements) experiences significant steric hindrance and cannot penetrate into the SC through aqueous pores that have an average radius of 29 +/- 5 Angstrom. We believe that this inability of the SCI micelles to contribute to SCI skin penetration and associated skin barrier perturbation is responsible for the observed skin mildness of SCI. Through in vitro quantitative skin radioactivity assays using (14)C-radiolabeled SCI and pig full-thickness skin (p-FTS), we also show conclusively that SCI skin penetration is dose-independent, an important finding that provides additional evidence that the larger SCI micelles cannot penetrate into the SC through the smaller aqueous pores that exist in the SC, and therefore, cannot induce skin barrier perturbation (1).

Sodium cocoyl isethionate (SCI) has been a predominant ingredient in syndet bar formulation for more than thirty years. Although cost effective and well recognized for good skin compatibility, SCI is not regularly found in liquid detergent systems due to its limited solubility in water. This study focuses on the understanding of enthalpy of solubilization, equilibrium of solubilization, and the structures and properties of sodium cocoyl isethionate and various surfactants. The purpose of this exercise is to help the formulator to find appropriate surfactant systems to keep sodium cocoyl isethionate in aqueous solution. The solubility of SCI in water is unfavorable in terms of enthalpy of solvation. When setting up equilibrium of solubilization, there are three possible phases, and three methods have been developed to prevent SCI from recrystallizing in aqueous solutions. The first focuses on tying CI ions within micelles made of secondary surfactants. The second focuses on the exchange of sodium ions with ammonium ions (and/or triethanolammonium). The third centers on emulsification of SCI and the subsequent change of micelles into emulsified oil drops. A combination of two or three of these methods will enable the formulator to use SCI as the primary surfactant in liquid detersive systems (2).

In conclusion, we can say that this component is quite safe for the skin.

• Molecular Formula C₂Na₆O₄₇S₂₀ 
• Peso molecolare  218.199
• CAS  61789-32-0    58969-27-0 
• UNII  518XTE8493
• EC number        263-052-5

References________________________________________________________________________

(1) Ghosh S, Blankschtein D. Why is sodium cocoyl isethionate (SCI) mild to the skin barrier? - An in vitro investigation based on the relative sizes of the SCI micelles and the skin aqueous pores. J Cosmet Sci. 2007 May-Jun;58(3):229-44. 

(2) Sun JZ, Parr JW, Erickson MC. Solubilization of sodium cocoyl isethionate. J Cosmet Sci. 2003 Nov-Dec;54(6):559-68.