Cocamide DEA
In plain terms
A coconut-derived foam booster made with diethanolamine. Listed by IARC as a possible carcinogen and by California Prop 65 as a known one, and it can form skin-absorbed nitrosamines. Gentler foam boosters do the same job.
What the evidence shows
Cocamide DEA is a foam booster and thickener made by reacting coconut fatty acids with diethanolamine, and it is the diethanolamine half that draws the concern. The cancer research agency classifies cocamide DEA as a possible human carcinogen, and California lists it under Proposition 65 as a chemical known to cause cancer, which is why products containing it can carry a cancer warning in that state. Those listings trace back to animal studies in which the cancer-causing activity tracked the amount of leftover free diethanolamine in the material. There is a second route to worry: free diethanolamine can react with other ingredients to form nitrosamines, a family of compounds that are carcinogenic and absorb through skin, which led the cosmetic safety panel to say these ingredients should not be used where nitrosamines can form. The honest limits matter too. The classification is possible rather than proven in people, the strongest data are from animals, and the panel considers it usable if nitrosamines are kept out. But this is a foaming agent with no unique benefit, it carries two separate cancer-linked concerns, and gentler stand-ins do the same job, so many brands have already dropped it. Avoiding it costs you nothing.
On the label
Listed as cocamide DEA or cocamide diethanolamine, mostly in shampoos, bubble baths, and shower gels for foam. Cocamide MEA and cocamide MIPA do the same job without the diethanolamine concern. In California it may carry a Prop 65 cancer warning.