Puberty delay and sexual immaturity are when puberty is 2.5 standard deviations later than the average age of sexual characteristics in the normal population. Puberty is called delayed. It usually refers to a girl who has not developed breasts after the age of 13, or has not had her first menstruation at the age of 15, or has not had her first menstruation 5 years after breast development. Puberty delay can be idiopathic or caused by various pathological factors. Children who have reached this age but still have no sexual characteristics should be distinguished from delayed puberty and permanent sexual immaturity. Strictly speaking, puberty delay refers to the delayed onset of puberty, so it is mostly idiopathic; while sexual immaturity refers more to the lack of puberty, often accompanied by congenital abnormalities.