It is normal for a 10-year-old boy to grow armpit hair. A 10-year-old boy growing armpit hair is a normal physiological development phenomenon, because males generally begin to sexually mature at the age of 10~13 years, and the individual’s gonads, sex organs, and secondary sexual characteristics develop rapidly and gradually mature, so as to have the ability to procreate. In males, this is mainly manifested by the enlargement of testicles and scrotum, and the growth and development of pubic hair, penis, armpit hair, chest hair and beard. If a boy develops these signs before the age of 9, he should be alerted to the possibility of precocious puberty, and if he does not develop these signs before the age of 15, he should be alerted to the possibility of precocious puberty. Parents are advised to pay attention to their children’s development during the growth period, and if any abnormality occurs, they should bring their children to the hospital in time to find out the cause of the disease, and then actively standardize the treatment under the guidance of the doctor.