Cocamidopropyl Betaine (CAPB) is a zwitterionic surfactant derived from coconut fatty acids: its molecule carries both a positively charged quaternary ammonium group and a negatively charged carboxylate group. It is found in the vast majority of shampoos, yet it is almost never the main cleansing agent. It works as a co-surfactant: it makes anionic surfactants milder, stabilises the lather, helps build viscosity and gives the fibre a light conditioning effect.
The name is misleading: CAPB is not made from natural betaine (trimethylglycine) found in sugar beet. “Betaine” here refers to a chemical family, molecules that combine a quaternary nitrogen with a carboxylate. Hairswiss explains its structure, how it behaves as pH changes, and the points to watch regarding its manufacturing impurities.
What is Cocamidopropyl Betaine?
CAPB is a mixture of closely related molecules whose fatty chain comes from coconut or palm kernel oil, mostly C12 (lauric acid). Its main component, Lauramidopropyl Betaine, has the formula C19H38N2O3 and a molar mass of about 342.5 g/mol.
It is made in two steps:
- Amidation: the fatty acids (or their methyl esters) react with dimethylaminopropylamine (DMAPA). The primary amine forms an amide bond, giving an amidoamine that keeps a free tertiary amine.
- Betainisation: the tertiary amine is quaternised with chloroacetic acid in the presence of sodium hydroxide. This creates the carboxymethyl group of the betaine and, as a by-product, sodium chloride.
The raw material is supplied as an aqueous solution of about 30% active matter. The European CosIng database lists its functions as cleansing surfactant, foam booster, hair conditioning agent, antistatic agent and viscosity controller.
How does the charge of CAPB change with pH?
The nitrogen in CAPB is bonded to four carbon atoms, so its positive charge is permanent at any pH. The carboxylate group, on the other hand, is a weak acid. A betaine can therefore exist in only two forms:
- zwitterionic (one positive and one negative charge, neutral overall) across the usual shampoo pH range;
- cationic in more acidic conditions, when the carboxylate is protonated and only the positive charge remains.
This cationic share explains why betaines condition better in low-pH formulas: the molecule is drawn to the anionic sites of keratin, especially on bleached hair rich in cysteic acid. It is also what sets betaines apart from true amphoterics of the amphoacetate type (Sodium Cocoamphoacetate), which can be anionic, zwitterionic or cationic depending on pH. Sultaines such as Cocamidopropyl Hydroxysultaine replace the carboxylate with a sulfonate that stays ionised, so they remain zwitterionic across the whole cosmetic pH range.
Why does CAPB make a shampoo milder?
How harsh an anionic surfactant is depends mainly on its free monomers, which penetrate the stratum corneum and the cuticle and bind to proteins. When CAPB is added to an anionic surfactant (sulfate, olefin sulfonate, sulfosuccinate), it enters its micelles and forms mixed micelles. Its zwitterionic head sits between the anionic heads and reduces their electrostatic repulsion: micelles form at a lower concentration and become more stable.
The result is fewer free anionic monomers in the wash liquor, and therefore a weaker interaction with keratin and scalp lipids. This is the main reason it is used in shampoos: to reduce the irritation that purely ionic surfactants would cause. The same principle underpins the mixed systems described in our articles on amino acid surfactants and isethionate and on Lauramidopropylamine Oxide, another co-surfactant with amphoteric character.
What role does it play in lather and viscosity?
CAPB makes the lather denser and more stable, especially in the presence of sebum, which tends to collapse the foam of anionics used alone. It also shapes the texture of the product. Combined with an anionic surfactant and sodium chloride, it helps spherical micelles grow into elongated, so-called “wormlike” micelles that entangle and raise viscosity. Beyond a certain amount of salt, viscosity drops again: this is the “salt curve” every formulator tunes.
This mechanism explains why so many INCI lists open with the sequence anionic surfactant, Cocamidopropyl Betaine, Sodium Chloride. In sulfate-free bases, where salt thickens less effectively, formulators add polymers. In formulas containing cationic polymers, the anionic-zwitterionic system also helps form the coacervate that deposits on the fibre during rinsing, a mechanism covered in our article on Polyquaternium.
Is Cocamidopropyl Betaine an allergen?
CAPB was named 2004 “Allergen of the Year” by the American Contact Dermatitis Society. Later work showed that sensitisation is mainly linked to two synthesis impurities: amidoamine (cocamidopropyl dimethylamine) and residual DMAPA. Some reactions described as allergic are also irritant in nature.
The Cosmetic Ingredient Review (CIR) concluded that CAPB and related amidopropyl betaines are safe in cosmetics when formulated to be non-sensitising. Its quantitative risk assessment found no sensitisation in finished products at 0.01% DMAPA in raw CAPB, whereas 0.5% amidoamine could sensitise in certain products. Leading manufacturers now specify less than 0.3% amidoamine and less than 15 ppm DMAPA. For professionals, the quality of the raw material therefore matters more than the presence of CAPB itself. If a client shows a suspected reaction, a patch test with a dermatologist will settle the question.
Which professional shampoos use CAPB as a co-surfactant?
NIKA Gentle Relief Shampoo, available on cliCHair.ch, is a good example of a dual-amphoteric system: it combines Sodium C14-16 Olefin Sulfonate with Cocamidopropyl Betaine and Sodium Cocoamphoacetate, without SLES or SLS. The two amphoterics soften the olefin sulfonate, while Polyquaternium-7 and Polyquaternium-22 improve detangling at the rinse, a consistent base for sensitive scalps. The chemistry of olefin sulfonate is covered in our article on Sodium C14-16 Olefin Sulfonate.
INEJ Smooth Shampoo by Code Zero, which Swiss professionals find on cliCHair.ch, shows the classic scheme: Ammonium Lauryl Sulfate, Cocamidopropyl Betaine and Sodium Chloride at the top of the list. The betaine tempers the sulfate and, together with the salt, builds viscosity; cationic guar and hydrolysed rice and soy proteins complete the smoothing effect.
How can you spot CAPB and related surfactants in an INCI list?
- Amidopropyl betaines: Cocamidopropyl Betaine, Lauramidopropyl Betaine.
- Alkyl betaines: Coco-Betaine, with no amidopropyl bridge and therefore no DMAPA or amidoamine impurities.
- Sultaines: Cocamidopropyl Hydroxysultaine, zwitterionic across the whole pH range.
- Amphoacetates: Sodium Cocoamphoacetate, Disodium Cocoamphodiacetate, imidazoline derivatives.
As with any surfactant, position in the list is decisive: a betaine in second or third place signals a major co-surfactant, whereas at the top of the list it points to a very mild base, often designed for reactive scalps. To place these systems within the logic of mild formulas, see also our analysis of sulfate-free formulations.
Conclusion
Cocamidopropyl Betaine owes its place in shampoos to its zwitterionic structure: a permanent positive charge and a pH-sensitive carboxylate. Inserted into the micelles of anionic surfactants, it reduces their harshness, enriches the lather and helps build viscosity. Its only known weak point lies in manufacturing impurities, now kept under control by supplier specifications. For hairdressers, reading it in an INCI list means understanding how the formula was made milder.