A coupler is generally an aromatic compound, either a benzene derivitive or a napthol. Couplers modify the color generated when used together with the primary intermediates and the oxidation ingredient (peroxide). Couplers are commonly classified into three
groups: Yellow-green, Red, or Blue.
Couplers "couple"("bond) with the products primary intermediates, which form the shade a
color product will produce, AND the couplers help bond these primary intermediates to the action
of the oxidative ingredient... peroxide. So, three things help a hair color product 'stick together" and create a new shade in the hair.
Primary Intermediates
Coupler
Oxidative ingredient
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