Background: While numerous papers have reported on the biological mechanisms of human hair pigmentation and greying, epidemiological descriptions of both natural hair colour and the greying process, worldwide, remain scarce.
Objectives: To assess hair colour and greying in a large world sample of human subjects, and to revisit the validity of the 50/50/50 rule of thumb, which states that 'at age 50 years, 50% of the population has at least 50% grey hair'.
Methods: The natural hair colour of 4192 healthy male and female volunteers was assessed using a sensorial expert evaluation through the comparison of each volunteer's hair with standard swatches. Hair colour was studied according to age, gender and ethnic or geographical origin.
Results: Overall we observed that between 45 and 65 years of age, 74% of people were affected by grey hair with a mean intensity of 27%. Men harboured significantly more grey hair than women. Both age at onset and rate of greying with age appeared to be clearly linked to ethnic/geographical origin. Subjects of Asian and African descent showed less grey hair than those of caucasian origin, at comparable ages, confirming previously reported data.
Conclusions: Calculating the percentage of people showing at least 50% grey hair coverage at age 50 years leads to a global range of 6-23%, according to ethnic/geographical origin and natural hair colour: well below that expressed by the '50' rule of thumb.
© 2012 The Authors. BJD © 2012 British Association of Dermatologists.