Final answer:
A patch test is required before the use of oxidative tints in hair coloring because these products contain allergens, and a patch test ensures that the client will not have an adverse reaction.
Step-by-step explanation:
Because most oxidative tints contain known allergens, prior to use they require a patch test to ensure the client does not have an adverse reaction. Permanent hair coloring involves a chemical reaction that occurs with three main components: (1) an aromatic amine such as 1,4-diaminobenzene or 2,5-diaminotoluene, (2) a coupling agent, and (3) an oxidant like hydrogen peroxide. The process usually happens in a basic (alkaline) environment.
The mechanism consists of:
- Oxidation of the amine to its quinone form,
- Reaction with the coupler, and
- Further oxidation to create the final dye pigment.
It's important to note that certain unapproved colorants such as those derived from natural sources like vegetables, animals, and minerals may not require certification but may be costlier and add unintended flavors when used in food. In contrast, synthetic dyes approved for use in foods and cosmetics are identified by FD&C numbers in the United States or E numbers in the European Union.
Due to the presence of chemicals like hydrogen peroxide which is an irritant, it's necessary to conduct a patch test to prevent complications like irritation to eyes and skin.