Ammonia

Also known as: Ammonium hydroxide; aqueous ammonia

INCI name: Ammonia; Ammonium Hydroxide

What it does

The traditional alkaliser in permanent colour. It raises the pH so the hair's outer layer swells and opens, letting the dye and peroxide in, and speeds up lightening of your natural pigment.

Benefits

Efficient at opening the hair and lifting colour. It is volatile, which is where the sharp smell comes from.

Concerns & Risks

An irritant rather than an allergen: it can sting and inflame the scalp, but it is not what causes the PPD-type allergic swelling. Leaving it out ('ammonia-free') only changes the alkaliser; it says nothing about PPD or other allergens in the same tube.

Comedogenic rating

0/5

Non-comedogenic (0)

Suitable for

Most people with an intact scalp, following the timing on the pack

Avoid if

Your scalp is broken, sunburnt or irritated

Typical concentration

EU maximum 6% (as NH3); above 2% the label must say 'Contains ammonia'. India and US: no specific limit verified.