Hair dyes – ingredient lists and INCI analysis

Permanent hair dyes usually come as two parts mixed just before use: a colour cream or gel and a developer containing HYDROGEN PEROXIDE. The mixture is applied to dry hair, left for the time stated in the leaflet and rinsed out, often followed by a conditioner supplied in the box. Semi-permanent and direct dyes work without a developer, and henna-type products are mixed with water.

Oxidative dyes rely on precursors and couplers such as P-PHENYLENEDIAMINE, TOLUENE-2,5-DIAMINE SULFATE, P-AMINOPHENOL, RESORCINOL or 2-METHYLRESORCINOL, which form colour inside the hair fibre. An alkalising agent, typically AMMONIA or ETHANOLAMINE, opens the cuticle. Direct dyes include substances such as HC BLUE NO. 2 or BASIC RED 51, while plant colours list ingredients like LAWSONIA INERMIS.

In the EU, hair dye substances are regulated individually in Annex III of the Cosmetics Regulation, with maximum concentrations after mixing and mandatory warnings. Packs of oxidative dyes carry a statement that hair colorants can cause severe allergic reactions, typically instructions for an allergy alert test to be carried out before each use, and a note that the product is not intended for persons under 16.

Because several dye ingredients are known sensitisers, many readers check the INCI list for the specific precursors used. The list on the colour component and the one on the developer are often printed separately, so it is worth reading both. Some products also list ingredients that are not dyes at all, such as conditioning agents, antioxidants like SODIUM SULFITE or chelating agents.