I’m often asked about combining fats and surfactants. These questions usually come as variations on these two themes:.
Can I add a foaming surfactant to a fat-based cleanser (like a cleansing oil or cleansing balm) to add lather?
Fat-based cleansers like cleansing oils and cleansing balms are mostly comprised of oil soluble ingredients like carrier oils, fatty thickeners, and esters. They typically use fat-soluble surfactants for rinse-off; these ingredients allow the fatty ingredients in the formulation to mix with water so they rinse off the skin easily. Common choices include solubilizers like Polysorbate 80 and PEG-40 Hydrogenated Castor Oil, and emulsifiers like Emulsifying Wax NF and Olivem 1000. These surfactants don’t create fluffy bubbles, but instead make a low, creamy sort of lather when the cleansing balm or oil is mixed with water—this is why these products are sometimes marketed as “oil-to-milk” cleansers.
You can add foaming surfactants to formulations like this, but:
If you use a water soluble foaming surfactant like Sodium Lauryl Sulfoacetate (SLSa), Cocamidopropyl Betaine, Sodium Cocoyl Isethionate (SCI), or Coco Glucoside in a high-fat product like a cleansing balm, it usually won’t add much (if any) noticeable lather. This is because, for these sorts of foaming surfactants, fat inhibits lather. I have included a low percentage of solid foaming surfactants like Sodium Cocoyl Isethionate (SCI) in anhydrous cleansing balms in the past; in a formulation like this they boost rinse off, but don’t add noticeable lather.
Something else to consider is that because these foaming surfactants are water-soluble, you may encounter solubility/stability challenges. A solid surfactant like Sodium Cocoyl Isethionate (SCI) or Sodium Lauryl Sulfoacetate (SLSa) will settle out of a cleansing oil and will need to be suspended in a balm formulation. A liquid surfactant like Cocamidopropyl Betaine or Coco Glucoside will contain quite a lot of water (often upwards of 50%). Not only will that water likely separate from the oil in your formulation, but it also means your formulation is no longer anhydrous so you will need to incorporate a preservative into your product.
If you want luscious lather in high-fat formulations, you’ll need use a special type of surfactant that does lather in formulations with lots of fat. These are MIPA and TIPA laureth sulfates; they’re not natural, but they are super duper cool! The easiest one to purchase is LUMOROL K 5229 (INCI: Laureth-4 & MIPA-Laureth Sulfate & Propylene Glycol). You don’t need much to get good lather (I’ve found 20–30% is enough), and even less for a creamy rinse-off. I do find LUMOROL K 5229 is a really effective cleanser, so even at 4% it’s a bit too strong for my tastes for a facial cleanser.
Can I add fat to a hydrous foaming liquid cleanser to make it gentler/richer?
This sort of cleanser is powered water soluble surfactants like Sodium Lauryl Sulfoacetate (SLSa), Cocamidopropyl Betaine, Sodium Cocoyl Isethionate (SCI), or Coco Glucoside. These surfactants are diluted with water and can be thickened (with gums, salt, Crothix™ Liquid) or left thin and put in a foamer bottle.
If a surfactant-based liquid cleanser like a shampoo or body wash isn’t designed from the ground up to contain and support a meaningful oil content, adding oil to it won’t work. The oil will separate out as there won’t be an adequate emulsifier present. Compare this body wash formulation without oil to this body wash formulation 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.
Of course you can incorporate an emulsifier so the oil will mix in, but once you start adding an emulsifier and oils to what began as a non-emulsified formulation, you’re changing it pretty dramatically. I wouldn’t say you’re making the same formulation anymore and are firmly in re-development territory. Emulsions containing foaming surfactants are also a challenge to keep stable, so be prepared to do lots of testing and experimenting to ensure it doesn’t split over time.
Happy formulating!
Posted in: Troubleshooting & Adjusting
