An investigation of dermatitis and subsequent hairloss revealed that hair colorants with monoethanolamines with peroxide induced oxidative stress and cell toxicity in human hair. This study compared ammonia based colorants to colorants with the non ammonia alternatives called monoethanolamines(MEA). The results affirmed that using the non ammonia colorants can cause hairless over time with repeated exposure and that minimal quantities of ammonia in hair colorants are not toxic.

source: Journal of Dermatology Science