Sodium Cocoyl Isethionate

Overview

Sodium Cocoyl Isethionate — often called “baby foam” in the formulating world — is one of the gentlest surfactants available. It is derived from coconut fatty acids and isethionic acid, producing a fine powder or compressed noodles that foam beautifully without stripping the skin or scalp. This is the surfactant you reach for when you want cleansing without compromise.

It earned the “baby foam” nickname because it is mild enough for infant skin. Unlike traditional soap (which is alkaline and can disrupt the acid mantle), SCI works at skin-friendly pH levels and leaves behind a soft, conditioned feel. It is the backbone of most modern syndet (synthetic detergent) bars and solid shampoo bars.

SCI comes in two common forms: a fine powder (easier to blend but dusty — wear a mask) and pressed noodles (less dusty, slightly harder to incorporate). Both perform identically once dissolved. The powder form melts faster, which makes it popular for melt-and-pour syndet bar methods.

What it does in a formula

SCI is a primary surfactant — it provides the cleansing power and the foam. Its lather is dense, creamy, and stable rather than thin and bubbly. In solid bars, it binds the mass together while delivering a luxurious wash-off experience that rivals high-end commercial bars.

In liquid formulations at lower percentages (3-15%), it acts as a secondary or co-surfactant that boosts foam density and mildness. Paired with other surfactants like cocamidopropyl betaine or decyl glucoside, it rounds out the lather profile and reduces overall irritation potential.

How to use

• Syndet bars: Use 30-70% SCI. Melt or press with a binding agent (such as cocoa butter, cetyl alcohol, or SLSA for extra bubble). Work at around 60-70°C. Press into molds while warm.
• Shampoo bars: 40-60% is the sweet spot. Combine with a conditioning agent (BTMS-50, cetrimonium chloride) and a butter for bar hardness.
• Liquid cleansers: Dissolve 3-15% in heated water (60-70°C), stirring until fully incorporated. It can take patience — SCI does not dissolve instantly.
• Always wear a dust mask when handling the powder form. The fine particles irritate airways.
• pH-adjust your final product to 5-6.5 for optimal skin compatibility.

Best for / Worst for

Best for: syndet shampoo bars, facial cleansing bars, bubble bars, baby wash, sensitive-skin body wash, sulfate-free cleansers, solid bubble bath.

Worst for: clear liquid formulations (it creates opacity), formulas where you need instant cold-water solubility, anhydrous products with no water phase.

Common pitfalls

Not dissolving fully — SCI needs heat (60-70°C) and time to dissolve in water. If you dump it into lukewarm water, you get gritty lumps that never integrate.

Skipping the dust mask — The powder form is extremely fine and irritates the lungs. Always wear respiratory protection when weighing and mixing.

Using it alone in liquid formulas — At low percentages in liquid, SCI produces thin lather by itself. Pair it with a co-surfactant (cocamidopropyl betaine, decyl glucoside) for a full foam profile.

Overloading in bars without enough binder — Above 60% SCI, bars can crumble if you do not include enough fatty binder (cocoa butter, cetyl alcohol, or stearic acid) to hold them together.

Ignoring pH — SCI functions best at pH 5-7. Going too acidic breaks down the foam; going too alkaline defeats the purpose of using a mild surfactant.

Substitutes

• Sodium Cocoyl Glutamate — amino acid-based surfactant, equally mild, better for liquid formulas but poor for bars.
• Sodium Lauryl Sulfoacetate (SLSA) — similar bar-forming ability and fluffier lather, slightly less mild but still gentle.
• Decyl Glucoside — non-ionic, very mild, liquid only. Cannot form bars.
• Cocamidopropyl Betaine — amphoteric co-surfactant, good foam booster but not a standalone primary in bars.