Canities, physiological L67.1

Pyhsiological graying of hair, also called achromotrichia, occurs with the normal aging process. However, the age at which it occurs varies among different ethnic groups. A large population-based study found that 6% to 23% of people have 50% gray hair by age 50 (Panhard S et al 2012).

Premature graying is defined as graying of hair before age 20 in Caucasians and before age 30 in people of color. The mean age of onset of graying is 34 ± 9.6 years in Caucasians and 43.9 ± 10.3 years in people of color.

The color of human hair is due to the pigment melanin produced by melanocytes localized in the hair bulb.

The human hair follicle contains two types of melanin: eumelanin and pheomelanin. The diversity of hair color results mainly from the amount and ratio of blackish-brown eumelanin and reddish-brown pheomelanin. The phenotype of the hair is influenced by the pH and the cysteine content of the melanosomes. If the pH decreases, there is a progressive decrease in tyrosinase activity. This leads to an increase in pheomelanin and to reddish or blond hair (Ito S et al. 2001; Ancans J et al.2001).

A mutation in the melanocortin-1 receptor(MC1R) gene causes auburn or red hair color. This mutation usually occurs in people in northern Europe who have less exposure to the sun (Rees J 2000; Rees JL 2006).