The absence of armpit hair can be caused by hereditary diseases, generalized baldness, and disorders of the hypothalamic-pituitary-adrenocortical axis. Hereditary diseases or family genetic factors may lead to the absence of armpit hair, and there is also the possibility of self-loss of hair or generalized baldness and other skin diseases, which can also cause the loss of eyebrows, eyelashes, hair, and so on. If the patient not only does not grow armpit hair, but also the development of secondary sexual characteristics is delayed or does not develop, it may be due to the hypothalamus pituitary adrenocortical axis dysfunction, resulting in the secretion of androgens to reduce the level of the phenomenon of the absence of armpit hair. In this case, it is necessary to go to the hospital to have the hormone level tested and treated. Armpit hair has the function of reducing friction in the armpits and dissipating heat and air. Patients who have no armpit hair, accompanied by other hair loss or developmental delay, should go to the regular hospital for examination and treatment.