When you are 30 years old and have gray hair on your head, the possible clinical causes are genetic factors, lack of nutrition, mental factors and other symptoms. 1. Genetic factors: this is the most common cause of the situation, when there are more people in the family in this situation, it suggests that there is a clear family genetic tendency, the probability of the family’s offspring to appear in the situation will also increase. 2. Lack of nutrition: part of the population’s own nutritional intake is insufficient, the body lacks trace elements, as well as vitamins, proteins, which are necessary elements for the production of melanin, and thus may appear gray hair. 3. Mental factors: the body is in a state of high tension for a long time, unbalanced and unhealthy sleep habits resulting in a poor mental state, the above conditions are prone to induce premature growth of gray hair. It is recommended that people with related conditions should go to the hospital for examination to make a clear diagnosis, so as to carry out targeted treatment.