The breasts of a ten-year-old girl start to develop without other uncomfortable symptoms, mostly considered as normal phenomenon. The timing of a girl’s breast development is affected by a variety of factors such as genetics, nutrition, race, etc. Usually, a girl’s breast development occurs around the age of 9 to 11. When the girl has no special symptoms, such as dizziness, headache, height abnormalities and other phenomena, then ten-year-old breast development is considered a normal phenomenon, do not need to worry too much. However, if a ten-year-old girl’s breasts have begun to develop, but are accompanied by height abnormalities, such as rapid growth, and are accompanied by varying degrees of dizziness, headaches and other symptoms, there is a relatively small chance that this is due to pituitary gland pathology, and further examination is needed. In addition, the development and size of a girl’s breasts are mainly controlled by the hypothalamic-pituitary-ovarian functional gonadal axis, and when any of the links are abnormal, it will lead to abnormal development. When a ten-year-old girl’s breasts start to develop, parents are advised to do a good job of psychological relief and inform her of the relevant precautions. In daily life, avoid chest bumping, etc.