research Comparison of damage to human hair fibers caused by monoethanolamine- and ammonia-based hair colorants. 4 citations , May 2014 in “PubMed” Monoethanolamine-based hair colorants can cause more damage to hair than ammonia-based ones.
research Understanding the Effect on Hair Fibers of Coloring and Bleaching Formulations Using High Pressure Differential Scanning Calorimetry (HPDSC) January 2007 Hair coloring and bleaching can permanently break down hair protein and temporarily change its properties.