Growing a gray hair may be related to age, stress and other physiological factors, but also may be caused by vitiligo and other diseases. 1. Physiological factors: ageing may cause the body to show signs of aging, and its hair will gradually become white, some people may appear to grow a white hair. In daily life, long-term mental stress, may also trigger the appearance of white hair. 2. Vitiligo: Vitiligo patients are mainly manifested as white spots on the skin, if the head and face with white spots, may lead to the local appearance of white hair. The cause of the disease is mostly related to genetic, autoimmune system diseases and other factors, mental, skin injury and other factors may also trigger the disease. The cause of a white hair is not unique, after excluding physiological factors, it is recommended to go to a regular hospital for examination to clarify the cause of the disease.