Hair Colouring by Using Catechins from Green Tea and Chemical Oxidants

The hair dyeing using green tea extracts containing high amount of catechins in combination with chemical oxidants such as O2, H2O2 and NaIO4 was attempted in order to establish a novel hair dyeing technique without using aromatic amines contained in commercial oxidation dye products. The new hair dyeing technique consists of a twostep colouration system. The first step is treatment of hair with tea extract solution and the second one is oxidation treatment. Three kinds of oxidation methods such as (1) treating hair with basic dyeing solution (pH = 11.5) supplied with large amount of O2 gas (O2 method), (2) treating hair with H2O2 solution (pH = 9.5) (H2O2 method), (3) treating hair with NaIO4 solution (pH = 7) (NaIO4 method) were attempted as the second oxidation treatment. The results show that once dyed hair is discoloured by H2O2 in the oxidation process and white hair is hardly coloured by the method. In contrast, white hair is dyed brown by the O2 or NaIO4 method, and the dyeability increases with increasing temperature of the first tea extract treatment. This may be due to the increase in the amount of dye precursors adsorbed onto hair by heating. Colour fastness of the hair samples dyed by the O2 and NaIO4 method to washing is almost same level as that by the commercial oxidation dyes. The NaIO4 method is more useful than the O2 method because the supply of O2 gas is unnecessary for the NaIO4 one and it uses the neutral solution.