Breast development usually starts bilaterally or unilaterally. Breast development may start unilaterally, and the two sides are not completely synchronized, however, there will not be a situation where one side simply develops and the other does not, but generally both sides develop, except that one side may be more obvious, and there are no other undesirable symptoms, which is usually a normal phenomenon. During puberty, you should choose the right size, comfortable and breathable underwear. If one breast remains undeveloped, or if there is a big difference in the development of both breasts, it may be due to breast hyperplasia, precocious puberty, consumption of hormone-containing foods, etc. It is recommended that the patient go to the hospital for a comprehensive examination, and then do the appropriate treatment according to the cause of the disease.