Generally speaking, you’d hope to replace any surfactant with one that is the same format (liquid or powder) and has the same charge (anionic, non-ionic, amphoteric, or cationic). A similar pH and active surfactant matter (ASM—the concentration of the surfactant, basically) would be nice, but those differences can be accommodated in the formulation. It is also nice if the surfactant has a similar feel and produces similar lather. You can look up this information in my surfactants table and in my Encyclopedia. Your suppliers should also be providing this sort of information.
As with all substitutions, the impact of the substitution on the final product is heavily influenced by how much of the ingredient is used (if it comprises 50% of a recipe using something else will have a much bigger effect than if it comprises 0.5%!), and how similar the substituting ingredient is.
You’ll also need to consider the jobs a surfactant is doing; foaming/cleansing is often job #1, but if it is also functioning as a solubilizer (Caprylyl/Capryl Glucoside often does) you’ll need to be aware of that and replace that functionality as well with something like polysorbate 20.
Another job a surfactant can be playing in a product is to make the blend milder; this is achieved by combining surfactants with different changes. Cocamidopropyl Betaine is very commonly used for this reason; it is amphoteric, and while it isn’t a great lathering/cleansing surfactant on its own it compliments anionic and non-ionic surfactants, making them milder and supporting lather. Cocamidopropyl Betaine is usually the most readily available amphoteric surfactant, which is why I use it so often. If you need to substitute Cocamidopropyl Betaine (or another amphoteric) surfactant you will want to use a different amphoteric surfactant, and those can be hard to find. You can try coco betaine, babassuamidopropyl betaine, disodium lauroampho diacetate, and sodium cocoamphoacetate.
If you have a solid surfactant that may work, but the recipe calls for liquid, you can try making your own solution of the solid surfactant in water to give it the right format and ASM. Not all solid surfactants dissolve happily in water—I find SCS is reasonably cooperative, while I’ve watched SCI sit in a jar of water for over a year without dissolving.
If the recipe calls for a solid surfactant and produces a solid or semi-solid end product, you will need solid surfactants—liquid surfactants simply will not do. If a recipe calls for a solid surfactant and produces a liquid end product you can likely use a liquid surfactant instead; just keep in mind that liquid surfactants typically have significantly lower ASM values, so you will need to adjust the formula to keep the final ASM the same. I go over how to do this with spreadsheets here.
You will also want to take into consideration the type of lather the surfactant produces, how mild it is, and how good of a cleanser it is. I know this can be hard to do if you haven’t worked with both of the surfactants, so you’ll want to read about both and see if the recipe gives any clues as to why a certain surfactant was chosen. If the recipe makes a really big deal about not substituting a certain surfactant, take that into account.
All that said—you probably aren’t going to create an absolute catastrophe substituting surfactants, so I wouldn’t worry about it too much. Whatever you make will still lather and clean, and if you don’t like it very much you can probably use it up in no time if you start using it as a body wash.
Posted in: Substitutions