In humans, all the different hair colors are due to just two types or forms of pigment (melanin) called eumelanins and pheomelanins, which look like grains of different pigment forms and sizes. The color we see and how we characterize it depends on one factor - whether these grains reflect the light or not. Eumelanins are the dark brown and black pigments while pheomelanins are the red and blonde pigments. Eumelanin and pheomelanin granule forms: 1 - eumelanin (long and dark pigment granules); 2 - pheomelanin (small and light dispersed pigment granules). The different colors of hair in different people are due to a combination of these two different basic biochemical structures. By mixing the two types together in different concentrations the many different shades of hair color are made.

 

Eumelanins are very strong, stable proteins made from tyrosine. The large eumelanin biochemical structure is formed by processing the amino acid tyrosine into dopa and dopamine and connecting several of these molecules together to form eumelanin. The key enzyme in this process is tyrosinase. The more tyrosinase activity the more eumelanin is formed. This is one method by which different people have different shades of brown to black hair color. More tyrosinase activity results in more pigment production and so a darker hair color. As we get older, tyrosinase activity increases. It is most active in middle age and thereafter tyrosinase activity decreases. There are also other biochemical mechanisms by which the shade of hair color is regulated. Several factors interact with tyrosinase to help regulate eumelanin production. In addition, another key limiting factor in hair color is the availability of the raw tyrosine ingredient. A lack of tyrosine availability means the tyrosinase enzyme make eumelanin at full capacity.

Pheomelanins are also made from the same tyrosine as eumelanins and the process is much the same with tyrosinase playing a key role. Pheomelanins are produced when an intermediate product in the eumelanin production pathway interacts with the amino acid cysteine. This results in the formation of a pheomelanin molecule which contains sulfur from the cysteine. These molecules are yellow to orange in color. So this is another way by which different shades of hair color can be produced. The more interaction there is between dopaquinone and cysteine the more yellow and orange pigments are produced.

Thus those people with darker hair have relatively more eumelanin production. People with true red hair produce more pheomelanin. The pathway to eumelanin formation is largely inhibited. Because people with red hair are less able to make the dark eumelanin pigment their skin is generally quite pale and burns easily with sun exposure. A study that analyzed the amount of eumelanin and pheomelanin in human hair suggested that black hair contains approximately 99% eumelanin and 1% pheomelanin, brown and blond hair contain 95% eumelanin and 5% pheomelanin; and red hair contains 67% eumelanin and 33% pheomelanin. Although people with dark hair may still produce the yellow - orange pheomelanin, it is largely masked by the dark eumelanin pigment and we cannot see much of it. However, the red - yellow pheomelanin is believed to cause the warm, golden, copper, burgundy or auburn tones found in some types of brown hair.

 

Chemical eumelanin and pheomelanin formula: 1 - black melanin eumelanin monomer, 2 - brown melanin eumelanino monomer, 3 - pheomelanin monomer.