Sodium cocoyl isethionate (SCI) is a sulfate- and ethylene oxide (EO)-free anionic surfactant that produces abundant, stable foam even in hard water. It outperforms many commonly used anionic surfactants and is known for its very low toxicity and mildness. The skin mildness of SCI has been attributed to the fact that its micelle radius is larger than the aqueous pores in the stratum corneum (the outer layer of the skin), preventing the surfactant from penetrating and irritation the skin.
The recommended pH range for SCI is relatively narrow, as the material may hydrolyze outside the safe window of 6–8, especially under highly acidic or alkaline conditions.
Due to its low solubility (~0.01% by weight in water at room temperature), SCI is primarily used in cleansing bars. The use of SCI in liquid formulations can be challenging at first. However, a little trick may save you time and frustration.
To prepare a 10% SCI solution in water, weigh 10 g of SCI powder into a beaker, add 90 g of demineralized water (scale proportionally if needed), and heat to 80 °C. Do not stir, let the powder melt into the water. The Krafft temperature (the point at which a surfactant dissolves significantly more readily in water, enabling micelle formation above its critical micelle concentration) of SCI is below 40 °C. Above this temperature, a layer of liquid SCI will form at the bottom. Once SCI has fully melted, stirring can commence. No precipitation will be observed after cooling to room temperature. However, upon standing, the solution will develop a milky, creamy texture.
SCI solubility can also be improved by blending it with cationic surfactants such as alkyl betaines in a 1:3 ratio (SCI:alkyl betaine) and mixing by hand until a homogeneous white paste is formed. This blend can then be added to water at room temperature and stirred until fully dissolved.
Sodium cocoyl isethionate naturally produces a dense, creamy foam with a luxurious feel, making it a popular choice in sulfate-free shampoos and cleansers. Its foaming behavior can be easily adjusted, as it blends well with most other surfactants. In addition, SCI is non-comedogenic, meaning it will not clog pores, and is often included in facial cleansers for acne-prone skin due to its gentle yet effective cleansing properties.
Safety tip: It is advisable to wear a face mask when handling SCI powder, as it can easily become airborne and may be inhaled.
