Ammonium Hydroxide is probably the most debated and misunderstood ingredient in professional hair colouring. Accused of damaging hair and posing health hazards, it remains nonetheless irreplaceable in the chemistry of permanent colour. Hairswiss analyses the science, clears up the misconceptions, and provides the professional with a precise guide for safe use.
What Is Ammonium Hydroxide: Basic Chemistry
Ammonium Hydroxide (INCI: Ammonium Hydroxide), also known as ammonia solution, is an aqueous solution of ammonia (NH₃ dissolved in H₂O). In aqueous solution it partially dissociates according to the equilibrium:
NH₃ + H₂O ⇌ NH₄⁺ + OH⁻
This reaction produces hydroxide ions (OH⁻), making the solution strongly alkaline: the pH of a 10% ammonia solution is approximately 11–12. This alkalinity is the core of its role in hair colouring.
Why Ammonium Hydroxide Is Indispensable in Permanent Colour
Hair has a naturally acidic pH between 4.5 and 5.5. At this pH, the cuticle is closed and compact. To permanently colour hair, three chemical processes all require an alkaline pH:
- Cuticle opening: the elevated pH (9–11) causes the hair shaft to swell and cuticle scales to lift, creating the channels through which colour penetrates.
- Activation of hydrogen peroxide: the alkaline pH decomposes H₂O₂ into oxidising radicals, which oxidise natural melanin, lightening the base colour.
- Polymerisation of colour precursors: small precursors (p-phenylenediamine and derivatives) penetrate the cortex and oxidise into large pigment molecules, permanently trapped inside the hair shaft.
Ammonia vs Alternatives: MEA, Ammonia-Free Systems
Ammonia-free colours use alternative alkalising agents, primarily MEA (monoethanolamine) and AMP (2-amino-2-methyl-1-propanol). Ammonia’s decisive advantage is that it is highly volatile: it evaporates during application and rinsing, leaving very few residues in the hair. Non-volatile alternatives may seem gentler to the nose, but they remain in the hair fibre longer after application — a factor often overlooked in “ammonia-free” marketing claims.
Health Risks: What the Professional Needs to Know
Ammonium Hydroxide is approved for cosmetic use under Regulation CE 1223/2009 (Annex III, no. 57) with a maximum concentration of 6% calculated as NH₃. The real risks under professional use conditions concern:
- Inhalation: the occupational exposure limit (OEL) is 20 ppm (8h TWA) under Swiss regulations (SUVA). A well-ventilated salon stays well below this threshold.
- Skin contact: may cause scalp irritation in sensitive individuals. The 48h patch test before application is standard good practice.
- Eye contact: highly irritating; immediate thorough rinsing with water required.
Effects on Hair Structure
Forced cuticle opening at pH 9–11 inevitably causes structural stress on the hair fibre. After repeated colouring treatments, the following can be observed:
- Increased porosity (cuticle scales no longer close fully)
- Reduced elasticity (approx. -15–25% after 10 oxidative treatments, according to ex vivo fibre studies)
- Loss of internal lipids (18-MEA, linoleic acid) with reduced shine
- Progressive thinning of the shaft with closely spaced treatments
This is why pre- and post-colour protocols using protein treatments (hydrolysed keratin, wheat protein) and lipid treatments (argan oil, macadamia oil) are essential to preserving fibre integrity over time.
Environmental Impact
Ammonia is naturally present in the environment and is readily biodegradable: it breaks down into nitrogen and water. In wastewater treatment plants, it is effectively removed through biological nitrification. Its environmental impact at cosmetic use concentrations is considered low. The plastic packaging of colouring products represents a significantly greater ecological footprint than the ammonia molecule itself.