Encyclopedia · surfactant
Sodium cocoyl isethionate
A mild anionic cleanser, the basis of many syndet bars, with good lab evidence of being gentle on the skin barrier and growing use in sulfate-free shampoos and shampoo bars.
What it is
Sodium cocoyl isethionate (SCI) is the sodium salt of coconut fatty-acid esters of isethionic acid. It is an anionic surfactant, but a comparatively mild one. It is poorly soluble, so it often appears in bars and pastes or with solubilisers.
How it works
Ghosh and Blankschtein proposed that SCI micelles are larger than the pores of the skin's outer layer, so they cannot get in and disturb the barrier (in vitro) (Ghosh 2007). A 2025 skin-microbiome study used isethionate-taurate body washes among others (forearm and leg, not scalp) (Cheviti 2025).
What the studies show
- SCI micelles (radius about 33.5 angstroms) were too big to pass the skin's outer-layer pores (about 29 angstroms), which the authors link to its skin mildness. This was in vitro only (Ghosh 2007).
- Mild cleansers, including isethionate-taurate body washes, strengthened skin microbiome networks without changing overall composition. It was skin, not scalp (Cheviti 2025).
- A review gives an overview of raw materials and the trend toward sulfate-free shampoo systems (Cornwell 2018).
The mildness evidence is mechanistic and skin-based. We found no controlled trial of SCI shampoos on hair or scalp outcomes.
Side effects and safety
Irritation is low, and we found few allergy reports.
Bottom line
One of the best "mild but still cleansing" anionics. A good fit for dry, curly or sensitive scalps and for shampoo bars, but plain SCI cleans less aggressively than a sulfate, so very oily scalps and heavy styling products may need an occasional clarifying wash. Direct trials in shampoo format are needed. Bar shampoos made with alkaline soap are a different story (see shampoo pH).
Studies 3
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
Result: Sodium cocoyl isethionate forms micelles of about 33.5 angstroms, larger than skin aqueous pores (about 29 angstroms), which the authors proposed explains its mildness.
Read the study ↗Cheviti B et al. Mild skin cleansers strengthen microbiome networks without affecting the skin microbiome. 2025
Tested: mild cleansers including isethionate-taurate body washes
Result: Mild cleansers strengthened skin microbiome networks without changing overall composition.
Read the study ↗Cornwell PA. A review of shampoo surfactant technology: consumer benefits, raw materials and recent developments. Int J Cosmet Sci. 2018
Result: Overview of shampoo surfactant raw materials, consumer benefits and trends in sulfate-free systems.
Read the study ↗Related
- Sodium lauroyl methyl isethionateA more soluble cousin of sodium cocoyl isethionate used as a mild cleanser in modern sulfate-free shampoos, with no independent studies of its own.
- Sodium cocoyl glutamateAn amino-acid-based cleanser that was among the best-tolerated surfactants in a 105-patient patch-test study, with no scalp or hair trials yet.
- Cocamidopropyl betaineThe most common helper surfactant in shampoo, which makes sulfate cleansers gentler, thicker and foamier, and a rare cause of scalp allergy that usually comes from manufacturing impurities.
- Sodium lauryl sulfateA cheap, strong cleanser and foamer that removes oil very well but is the most irritating common shampoo surfactant, so dermatologists use it as their standard test irritant.
- Shampoo pHHair and scalp prefer mildly acidic conditions, but most shampoos are less acidic than that and the case for lower pH rests on lab mechanism rather than wear trials.