It may be normal for eight and a half year old girls to start developing breasts. However, it may also be caused by premature sexual development. Precocious puberty usually refers to the development of secondary sexual characteristics in girls before the age of eight, so the development of breasts in girls aged eight and a half may be a physiological phenomenon. Under normal circumstances, girls’ breasts start to develop after the age of nine to eleven. Eight and a half years old girls appear breast development, may be because nowadays the economic level is more developed, nutrition is more sufficient, may lead to premature mammary gland development, this is a normal physiological phenomenon. If the eight and a half year old girl’s breast just appeared breast knot, there is a slight pressure pain, indicating that the child is just appearing to develop, after the age of eight years old breast development, is not the scope of the definition of precocious puberty. However, we should also pay attention to premature sexual development caused by early breast development. Usually life should pay attention to the progress, if the breast continues to increase, height acceleration, parents should take the child to the regular hospital in time to identify the cause of the disease, under the guidance of professional doctors to take targeted treatment.