Acid Blue 9

Safety Information

Acid blue 9, when certified by the Food and Drug Administration (FDA), is referred to as blue 4 and can be used in coloring externally applied cosmetics. Please refer to blue 4 for more information on the certified color.

More information about the hair dyes.

In the European Union, acid blue 9 is permitted for use in non-oxidative hair dye products at a maximum concentration of 0.5% (see Annex III). Acid blue 9 is listed as CI 42090 and may be used as a coloring agent in cosmetics and personal care products (See Annex IV).

The European Commission’s Scientific Committee on Consumer Products and Non-Food Products for Consumers (SCCNFP) concluded that acid blue 9 at a maximum concentration of 0.5% in hair dye products does not pose a risk to the consumer.


Acid Blue 9

What Is It?

In cosmetics and personal care products, acid blue 9 is used in the formulation of hair coloring products.

Why Is It Used?

Acid blue 9 imparts color to hair. The exact color obtained will depend on the other ingredients that are used in the preparation and the starting color of the hair.

Scientific Facts

Acid blue 9 is a synthetic pigment sometimes referred to in general terms as a triphenylmethane color.

Hair dyeing formulations belong to three categories – temporary, semi-permanent and permanent coloring of hair. The permanent hair dyeing formulations are often referred to as oxidative hair dyes which are generally marketed as two-component products. One component contains the compounds (precursors) that become the colorants and the other component is a stabilized solution of hydrogen peroxide. The two components are mixed immediately prior to use.

The precursors and peroxide diffuse into the hair shaft, where color formation takes place after the ingredients combine to produce the coloring mixture. The precursors are oxidized by the hydrogen peroxide to form the colorant molecules.

These molecules are too large to escape from the hair structure. The hydrogen peroxide in the oxidative hair dye product also serves as bleaching agent for the natural pigment of the hair. The color that is formed depends on the precursors and direct dyes present in the dyeing solution, pH of the dyeing solution and the time of contact of the dyeing solution with the hair.