Gray hair to black hair at 18 years old needs to be treated according to the cause of the symptom. If it is caused by genetic factors, it is recommended to supplement the body’s lack of nutrients under the guidance of the doctor for treatment, if the formation of melanin particles is blocked, it is recommended to take drugs to supplement melanin. 1. Genetic factors: If one of the parents is born with white hair, the child may also develop white hair due to genetic reasons. It is recommended to take medicines such as folic acid tablets and vitamin B6 tablets for treatment under the guidance of doctors. The medicine can replenish the nutrients needed by the body and improve the symptoms. 2. Obstruction of melanin granule formation: Normally, hair papilla contains abundant blood vessels, which provide sufficient nutrients to the hair papilla and the hair bulb, enabling the smooth synthesis of melanin granules. When the formation of melanin granules in the hair papilla is blocked, gray hair will appear, resulting in the reduction and disappearance of melanin granules in the medulla and cortex of the hair. It is recommended to take medication to supplement melanin, such as hair pills and shouwu tablets, under the guidance of a doctor for treatment, and the medication, to a certain extent, can make the hair black. If the phenomenon of white hair at the age of 18, you should go to the hospital in time for targeted examination and treatment to avoid delaying the treatment of the disease.