Developer

In oxidative colour, hydrogen peroxide helps oxidize dye ingredients so colour molecules form in the hair. With lightener, it supports the chemical reactions that reduce natural or artificial pigment. The outcome depends on the whole formula; developer alone does not identify how much lift or deposit a service will produce.

Developer is usually labelled by percentage or volume. Those measures describe peroxide strength, but they are not a universal recipe. Different colour and lightener systems specify their own compatible developer, ratio, timing, and permitted uses.

A colourist considers the client's starting level, target shade, grey coverage needs, previous colour, hair porosity, and whether the formula will touch the scalp. They then follow the manufacturer's system directions. Strand testing may be useful when the colour history or hair condition makes the result uncertain.

Using more peroxide than a formula calls for does not simply make colour work faster. It can change lift, deposit, comfort, and hair condition, and it may produce a result that the colour line was not designed to deliver.

Tell the colourist about previous permanent colour, lightener, henna, smoothing treatments, and any past reaction to hair dye. Ask what the planned service can realistically achieve in one visit and whether a strand or allergy test is required under the product directions.

Developer and oxidative dye can irritate some people. Follow salon and manufacturer testing instructions, and do not use a scalp colour service on broken or irritated skin. This glossary explanation is not a mixing guide for at-home chemical processing.