Breast swelling, nipple pain and nipple color deepening are usually caused by mastitis, endocrine hormone disorders and breast hyperplasia. 1. Mastitis: Mastitis is a secondary inflammation caused by the blockage of breast ducts, and patients will experience symptoms such as breast swelling and pain, pus and breakage, and nipple color changes. 2. Endocrine hormone disorders: Endocrine hormone disorders are mainly caused by elevated estrogen, and patients will experience symptoms such as breast swelling and pain, nipple pain, and nipple color darkening. 3. Breast hyperplasia: Breast hyperplasia is mainly related to abnormal hormone levels in the body, which will lead to breast swelling, pain and nipple darkening symptoms. At the same time, breast swelling, nipple pain, nipple color deepening may also be caused by lobular hyperplasia, breast cancer, etc. It is recommended that the patient go to the hospital for examination, a clear diagnosis, and symptomatic treatment under the guidance of the doctor.