Cocamidopropyl betaine (CAPB) may behave as a zwitterion, which is a "chemical compound that carries a total net charge of 0 and is thus electrically neutral, but carries formal charges on different atoms." It has different behaviours depending on the pH. In alkaline solution (over pH 8) it behaves as an anionic surfactant with good foaming and detergency properties. In acidic solution (under pH 6), it behaves as a cationic surfactant that is substantive to our hair and skin that can increase mildness.
CAPB is never used alone in a formulation; you'll always use it as a secondary surfactant. It offers great foam stabilizing and a reduction in the irritant level of the anionic surfactants. It offers a great flash foam and some humectant properties. Because it behaves as a cationic in our products - because our pH should be below 7 - we find an increase in moisturization of our hair or skin and some anti-static properties. CAPB is a great thickener for alkyl sulfates (like SLS) or alkyl ether sulfates (like SLeS and ALeS).
I generally use Amphosol CG as my cocamidopropyl betaine choice, which is about 30% active CAPB. It has a pH of 5 to 7, and at 10% it has a minimal effect on skin and eye irritation (so you need to use about 35% before you reach this amount).
I use CAPB in every single surfactant creation I make because of all the lovely qualities listed above. In shampoos, it behaves as a humectant and a light conditioner. In body washes, it behaves as a humectant and offers some moisturizing to my skin. In bubble baths, it offers good flash foam and stabilization to the bubbles. If you are planning to make any of these types of products, stock up on CAPB!
In very mild or baby type cleansers, CAPB might be used as the primary surfactant with something like decyl glucoside (non-ionic) for a very very mild cleanser without a lot of foaming, a nice feeling of moisturizing, and some conditioning. If you have ridiculously dry skin, consider making a cleansing product using CAPB and decyl glucoside!
CAPB is suitable for all skin types as it is a mild cleanser that makes the other surfactants even more mild. It offers hygroscopic features - which benefits every skin type - and moisturizing through substantivity. In short, as a secondary surfactant, it's fantastic for everyone!
Foamer bottle facial cleanser (part 2)
Shampoo bars (without CAPB, but I'd suggest using 10% in place of one or other or both of the surfactants)
Join me tomorrow for fun with non-ionic surfactants!