• According to the research done by Wella Professionals, ammonia is one of the best technologies in permanent hair colours for long lasting colour performance and protection needed to maintain hair’s natural sheen and shape. It provides excellent grey coverage and pure colour results without compromising hair vitality. Being a small molecule, ammonia finishes its task and evaporates immediately. That explains the strong smell. • Since MEA must be used in a higher concentration in permanent hair colour, it also needs higher peroxide levels and a longer saturation time. This means the use of more oxidants, which are responsible for irritation and harm to the hair. The main advantage of MEA over ammonia is reduction of chemical smell; however that doesn’t mean superior hair protection compared to ammonia. • The combination of a higher concentration of MEA (v/s a semi-permanent hair colour) and the fact that it is a heavier molecule, which is harder to wash out, means that it stays on the -hair and can cause more damage.