Hair turning gray at the age of forty may be caused by physiological reasons, or may be caused by pathological reasons such as vitiligo. It can be blackened by supplementing micronutrients, ensuring regularity of life, and using topical macrolide immunosuppressants or oral glucocorticoid drugs. 1. Physiological reasons: with age, the tyrosinase activity of hair follicle melanocytes gradually decreases, and the melanocytes in the hair follicle will also decrease, causing the hair to become white, which can be relieved by supplementing trace elements and ensuring regular life. (1) Supplementation of trace elements: when the body lacks trace elements, such as copper, it may cause gray hair, so it is recommended that patients undergo a trace element examination and supplementation; for example, supplementation of multidimensional elemental tablets, Zancun tablets and so on. (2) Ensure regularity of life: when the human body does not have enough sleep and mental stress, it will cause hair to turn gray, so it is especially necessary to ensure regularity of life. 2. Pathological causes: If the hair turns white due to vitiligo, it can be treated by external macrolide immunosuppressants, such as tacrolimus ointment, oral glucocorticoids, such as prednisone. It is recommended that patients go to the hospital for examination in time, after clarifying the cause of the disease, under the guidance of professional doctors.