Sodium Cocoyl Isethionate: The Heart of Syndet Bars

If you have ever wondered why some solid cleansing bars feel noticeably gentler on your skin than a classic bar soap, there is a good chance sodium cocoyl isethionate is doing the work. It is the surfactant behind most of the "syndet bar" category, and it is worth understanding both chemically and regulatorily if you are formulating one.

What SCI actually is

Sodium Cocoyl Isethionate, often shortened to SCI, is a mild anionic surfactant made from coconut fatty acids and sodium isethionate. Its CAS number is 61789-32-0, though as with many surfactants derived from natural fatty acid mixtures, you may encounter it listed under related registry numbers depending on the supplier's exact process and blend. Its INCI name, Sodium Cocoyl Isethionate, is what belongs on your filing and your ingredient list; the trade names suppliers use for their SCI powders or noodles never go on a Cosmetic Notification Form directly.

Chemically, SCI sits in a sweet spot. It cleanses effectively, generates a dense creamy lather, and does so with less disruption to the skin's surface lipids than harsher sulfate surfactants. That mildness is the entire reason syndet bars exist as a category: they are marketed as an alternative for people who find true soap or sodium lauryl sulfate bars drying.

Why "syndet" and not "soap"

The term syndet is short for synthetic detergent, and the distinction matters for both formulation and regulatory reasons. True soap, meaning alkali salts of fatty acids sold with only a cleansing claim, can be treated differently from a cosmetic in some markets. A syndet bar built around SCI is a different chemical class entirely: it is a surfactant-based bar, not a saponified fat, and it is formulated and filed as a cosmetic rather than under whatever narrower treatment applies to true soap. If your bar also carries a cosmetic claim like moisturizing, brightening, or anti-acne, it is a cosmetic regardless of format, and that applies to soap bars too.

Formulation notes that affect compliance

SCI does not dissolve or process the way ordinary soap does. It needs heat and specific processing (often described as the "SCI dough" method, working it like a stiff paste before pressing into bars) to form a usable bar. That is a manufacturing detail, but it has one compliance-relevant consequence: because SCI is usually blended with co-surfactants, oils, and butters to get a workable, moldable bar, your actual finished formula is rarely SCI alone.

That means your filing needs the full ingredient list, not just the headline surfactant, and you need real percentages carried through for anything supplied as a blend. If your SCI arrives pre-blended with a co-surfactant like sodium cocoamphoacetate or a superfatting oil already mixed in, you have to expand that blend into its individual INCI components and multiply each by the blend's use level in your formula to know what you are actually declaring.

Quick reference

Detail	Value
INCI name	Sodium Cocoyl Isethionate
Common CAS number	61789-32-0 (verify against your specific supplier's documentation)
Function	Mild anionic surfactant, cleansing agent
Typical use level	Often 10 to 30 percent of a syndet bar base, varies by formula
Category note	Not true soap; a syndet bar with any cosmetic claim files as a cosmetic
Notes for filing	Confirm whether your SCI arrives as a blend and expand it to real components

What to check before you file

Before you submit a Cosmetic Notification Form for an SCI-based bar, confirm three things. First, that every co-ingredient in your SCI powder or noodle supply, not just the SCI itself, is captured with its own INCI name. Second, that any fragrance in the bar is checked against the incoming allergen disclosure thresholds, since bars are typically rinse-off products with a 0.01 percent trigger rather than the lower leave-on threshold. Third, that nothing in your superfatting oils or exfoliants appears on the Cosmetic Ingredient Hotlist at a restricted level.

Syndet bars are popular precisely because they read as a hybrid: soap-like format, cosmetic-grade mildness. That hybrid identity is exactly where compliance mistakes creep in, and it is the kind of ingredient-mapping work Cosmetic Comply was built to catch, tracing your SCI supply back to its real INCI components before the filing goes out the door.