Hair Pigment Structure and Chemical Oxidation

The principal pigments of human hair are the brown-black melanins (eume-lanins) and the less prevalent red pigments (pheomelanins). These latter pigments at one time were called trichosiderins. For this discussion, the brown-black pigments of hair will be referred to as melanins, and the yellow and red pigments will be referred to as pheomelanins. 

Given that the pigment granules of human scalp hair are located primarily in the cortical cells and the medulla, it is reasonable to assume that pigment degradation by chemical means is a diffusion-controlled process. However, evidence supporting this contention is not available at this time. 

Nicolaus s random polymer proposal is of special interest, because other polymers in nature contain regular repeating structural units (e.g., proteins, carbohydrates, and nucleic acids) and the structure he proposes deviates from these other naturally occurring polymers. 

In contrast to the random polymer proposal of Nicolaus, Mason has proposed that melanin is a homopolymer of 5,6-dihydroxyindole.This proposal is consistent with, and in a sense biased by, the regularity of other natural polymers. 

The Nicolaus group has isolated several pyrole carboxylic acids and indole derivatives from degradation studies of melanins [11, 56-58]. Among these degradation products are the following pyrole carboxylic acids  

---