Encyclopedia · chemical treatment
Ammonia and monoethanolamine (MEA)
The alkaline agents that swell the cuticle so dye and bleach can enter; "ammonia-free" MEA dyes are not gentler.
What it is
Ammonia (as ammonium hydroxide) is volatile and smelly and escapes after application. MEA is a non-volatile amine used in "ammonia-free" dyes. Both are cosmetic alkalizers.
How it works
A high pH swells the fibre, opens the cuticle and boosts peroxide activity. MEA stays on the hair and reacts with hair protein because it is more reactive than ammonia. Bailey 2014
What the studies show
- A Procter & Gamble study used infrared analysis, electron microscopy and protein-loss tests on swatches. Every method showed more damage from MEA formulas, up to 85% more than ammonia in the most extreme case. The authors suggest reducing ammonia's volatility rather than switching to high MEA. Bailey 2014
- This is the only comparative study we found, and it comes from an industry group.
How it's used in studies
Alkalizer levels in commercial colour are set by the maker. The study tested the upper range of MEA used on heads.
Side effects and safety
Ammonia fumes irritate the eyes and airways. The authors report that MEA is more irritating at high levels. Scalp stinging is common with both.
Bottom line
"Ammonia-free" mostly means less smell, not less damage. Choose by comfort and by the lift you need. See bleach and colour damage.
Studies 1
Bailey AD et al. Comparison of damage to human hair fibers caused by MEA- and ammonia-based hair colorants. J Cosmet Sci. 2014
Tested: monoethanolamine versus ammonia colourants
Result: Colourants with monoethanolamine caused up to 85% more damage than ammonia-based ones.
Read the study ↗Related
- Hydrogen peroxideThe oxidiser in every bleach and permanent dye; it lifts colour by destroying melanin but also oxidises the hair's own proteins, so damage rises with strength and repeat use.
- p-Phenylenediamine (PPD)The main dark permanent dye ingredient and one of the commonest hair-dye allergens; it colours well but can cause severe contact dermatitis in sensitised people.