To make cocamidopropyl betaine one reacts coconut oil with 3-dimethylaminoproplylamine (DMAPA) producing cocamidopropyl dimethylamine, which is then allowed to react with sodium monochloroacetate to get CAPB (cocamidopropyl betaine). CAPB can still contain varyng amounts of the initial reactants and intermediate chemicals, including amidoamine a known allergen. Natural? You decide.
CAPB is an obvious contributor to contact dermatitis and thus in addition to the fact that it is not natural, should be avoided if one is looking for natural products, in my opinion.
Foti C, Bonamonte D, Mascolo G, Corcelli A, Lobasso S, Rigano L, Angelini G. The role of 3-dimethylaminopropylamine and amidoamine in contact allergy to cocamidopropylbetaine. Contact Dermatitis. 2003 Apr;48(4):194-8. PMID 12786723
Fowler JF Jr, Zug KM, Taylor JS, Storrs FJ, Sherertz EA, Sasseville DA, Rietschel RL, Pratt MD, Mathias CG, Marks JG, Maibach HI, Fransway AF, Deleo VA, Belsito DV. Allergy to cocamidopropyl betaine and amidoamine in North America. Dermatitis. 2004 Mar;15(1):5-6. PMID 15573641