It is normal for girls to have hard lumps in their breasts at 0 months of age. Within 2 weeks of age, due to the influence of high maternal estrogen levels, hard lumps in the breasts usually do not require treatment and can disappear on their own after 2 weeks of age. If there is progressive breast enlargement or vulvar discharge within 2 weeks of age, it cannot be ruled out that the body is disturbed by other factors that cause high estrogen levels or congenital pituitary lesions, and in this case, a detailed examination of the pituitary gland and related hormone tests should be conducted at the hospital. Treatment is required with oral Chinese medicine or intravenous gonadotropin-releasing hormone analogs to intervene in sexual development. So once a girl finds a hard lump in her breast, she should be closely observed for enlargement, if not it can usually disappear on its own at the age of 2. If it does, go to the hospital for an examination.