The main reasons why babies do not grow hair include the following: First, trace element deficiency, such as zinc, iron, calcium and other trace element deficiency. Second, vitamin deficiency, such as vitamin A and vitamin D deficiency, can cause poor hair growth in children. In addition, folic acid and vitamin B12 deficiency can also cause children do not grow hair. Third, the scalp has fungal infection. Fourth, some endocrine diseases can also cause poor hair growth, such as hypothyroidism, phenylketonuria, etc. Parents are advised to take their children to the hospital to do trace elements, vitamins and other related examinations, and give appropriate supplements according to the examination results. In addition, endocrine tests should also be done to rule out hypothyroidism and phenylketonuria.