The growth of armpit hair in boys is only a manifestation of secondary sexual characteristics, it does not mean that puberty will end, the growth of armpit hair is mainly due to the role of androgens. Pubertal development in boys starts around the age of 9, due to the hypothalamus promoting the pituitary gland to secrete gonadotropins, including luteinizing hormone and follicle stimulating hormone, which promotes the production of androgenic testosterone by the interstitial cells of the testes, and the development and growth of androgen-sensitive tissues. The marker of puberty initiation in boys is testicular enlargement, with testes at 4 ml as a marker of puberty initiation. The average age of the onset of puberty in boys is around 9 years old, and after the onset of puberty, testicular enlargement and height growth are accelerated, and pubic hair and axillary hair generally begin to grow in the second year of puberty initiation. The sign of the end of puberty in boys is not the growth of pubic and axillary hair, but the growth of pubic and axillary hair only represents the action of androgens, which is not parallel to the end of puberty, and the sign of the end of puberty in boys is the first appearance of seminal emission.