Chapter 2: Other surfactants · Part 3: Amphoteric surfactants
Alkyl betaines
- Contaminant risk
The worst fact: coco-betaine at 16% and 30% and lauryl betaine at 10% were eye irritants in tests, and in people, lauryl betaine irritated skin at 1% and 10% (but not at 0.1%).
Why brands use it: a co-surfactant.
Take care if: it could splash in your eyes.
Comes from: fatty dimethylamines from coconut reacted with chloroacetic acid. One manufacturer's coco-betaine raw material is about 31% betaine, 7% salt and 62% water.
Myth check: "Coco-betaine is the same as cocamidopropyl betaine": no. It's made without DMAPA, the step that leaves CAPB's allergy-causing impurities.
Contaminants: monochloroacetic acid (Australia: "Toxic if swallowed...") and dichloroacetic acid, up to 100 ppm each in one manufacturer's coco-betaine. They're unlikely in a well-made product, but it's a factor you can't see on the label.
Fair to say: a US cosmetic review (2018) found them safe "when formulated to be nonirritating", with allergy only in case reports. The US EPA's Safer Choice list rates both a green circle.
Correct as of November 2026. What the badges mean
Sources
- Safe Work Australia. Hazardous Chemical Information System (HCIS): classifications for alcohol ethoxylates, C10-12 alcohol EO/PO, cocamidopropyl betaine, nonylphenol, DODMAC, and for ethylene oxide, propylene oxide, dimethyl sulfate, methyl chloride, benzyl chloride, epichlorohydrin, DMAPA, monochloroacetic acid and 1,4-dioxane.
- Cosmetic Ingredient Review: alkyl glucosides (2013); poloxamers (2008); cocamidopropyl betaine and amidopropyl betaines (2012); alkyl betaines (2018); alkyl sultaines (2024); lauriminodipropionates (2013); coconut oil and related ingredients (2011); fatty acids and fatty acid salts (2019).
The full source list is at the end of Chapter 2.