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.