Gray hair can be caused by physiological factors, heredity, diseases or mental factors, etc. Some of them can be blackened, while some of them are difficult to recover. Physiological factors, such as gray or white hair in old age, as well as genetic factors, such as progeria, albinism, Werner syndrome, etc. caused by gray hair can not be black again, and can be dyed and other methods to change the color of hair. Disease factors, such as vitiligo, pernicious anemia, hyperthyroidism, etc., can lead to gray hair, the patient can be actively treated by the primary disease, after controlling the primary disease, gray hair can gradually return to normal and become black. In addition, gray hair caused by emotional tension, severe mood swings, fear and other mental factors, can be adjusted through the mind, and then gradually recover. It is recommended to consult a dermatologist in a hospital to clarify the cause of gray hair and follow the doctor’s instructions.