Can I add a surfactant to this mostly fat-based formulation (or vice versa)?

I’m often asked about combining fats and surfactants. These questions usually come as variations on these two themes, which I’ll discuss briefly here.

A maker wants to add a foaming surfactant to a fat-based cleanser (like a cleansing oil or cleansing balm) to add lather.

This can be done, but it usually won’t add much (if any) noticeable lather. This is because fat inhibits lather, and a fat-based cleanser contains a lot of fat—those sorts of formulations are almost entirely fat! Something else to consider is that many foaming surfactants are water-soluble, so you may encounter solubility/stability challenges.

A maker wants to add fat to a foaming, water-soluble surfactant-based cleanser to make it gentler/richer.

If the surfactant-based cleanser isn’t designed from the ground up to contain and support a meaningful oil content, this won’t work—the oil will separate out as there won’t be an adequate emulsifier present. Compare this formulation without oil to this one with oil to see how different they are. The fact that oil inhibits lather also comes into play here; the oil in the formulation will reduce the lather the cleanser produces.

Posted in: Troubleshooting & Adjusting

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