Cocamidopropyl betaine

Cocamidopropyl betaine (CAPB) is a zwitterionic surfactant with a quaternary ammonium cation in its molecule. It is a viscous pale yellow transparent liquid and is used as a surfactant in bath products like shampoos and hand soaps, and in cosmetics as an emulsifying agent and thickener, and to reduce irritation purely ionic surfactants would cause. It also serves as an antistatic agent in hair conditioners.

Cocamidopropyl betaine is a derivate of cocamide and betaine. See cocamide for the discussion of the length of carbon chain in the molecule.

Cocamidopropyl betaine is a medium strength surfactant which most often does not irritate skin or mucous membranes. That said, some studies indicate it is an allergen. It also has antiseptic properties, making it suitable for personal sanitary products. It is compatible with other cationic, anionic, and nonionic surfactants.

Cocamidopropyl betaine to a significant degree has replaced cocamide DEA.

CAPB Specification
CAPB is obtained as an aqueous solution in concentrations of about 30%.
 * Active ingredient		29.5 – 32.5 %
 * Water				62 – 66 %
 * NaCl			       4.6 – 5.6 %

Typical impurities of leading manufacturers today:
 * Sodium monochloroacetate	< 5 ppm
 * Amidoamine (AA)		       < 0.3 %
 * DMAPA 			       < 15 ppm
 * Glycerol			< 3%

However, there are qualities in the market with up to 3% AA.

The impurities AA and DMAPA are most critical, as they have been shown to be responsible for skin sensitation reactions. These by-products can be avoided by a moderate excess chloroacetate and the exact adjustment of pH value during betainization reaction accompanied by regular analytical control.

Safety concerns relating to CAPB
CAPB has been claimed to cause allergic reactions in some users,  but a controlled pilot study has found that these cases may represent irritant reactions rather than true allergic reactions. Furthermore, results of human studies have shown that CAPB has a low sensitizing potential if impurities with amidoamine (AA) and dimethylaminopropylamine (DMAPA) are low and tightly controlled. Other studies have concluded that most apparent allergic reactions to CAPB are more likely due to amidoamine.