Common causes of hair loss in four-year-old children include the following: 1, trace element deficiency: such as zinc, iron, calcium and other trace element deficiencies. 2, vitamin deficiency: such as vitamin A, vitamin D deficiency, as well as folic acid and vitamin B12 deficiency, can cause megaloblastic anemia, which can also lead to hair loss and poor hair growth. 3, psycho-psychological factors: if the child is mentally stressed, stress Excessive stress can also cause hair loss. 4, endocrine diseases: such as hypothyroidism, phenylketonuria, etc. 5, other causes: papillary skin fungal infection, lack of sleep, etc. It is important to find the cause of hair loss according to the different clinical manifestations of the child, and then to treat the cause.