A mother in her 30s used to breastfeed her toddler for almost 10 months 5 years ago. In the last 3 months, the whole left breast continued to become large and uncomfortable with mild pain, anemia, low back pain and bilateral calf edema combined and severe. She had no family history of breast cancer, no estrogen use, no breast trauma, and no systemic disease. Finally, she was diagnosed with idiopathic granulomatous mastitis by tissue section. After minimally invasive drainage surgery combined with anti-inflammatory medication, the patient responded well, the breast lumps completely subsided, and the clinical discomforts, such as anemia, improved and she recovered her health. Mastitis is common in lactating women, but it can also occur in non-lactating women. It is characterized by red, swollen, hot and painful lumps in the breasts, which may be accompanied by fever and generalized weakness. Inadequate breastfeeding or improper handling of blocked mammary glands can lead to tissue damage and bacterial infection. Dietary factors or prolonged intervals between feedings can cause thick and stagnant milk, which can also lead to mastitis. Simple obstruction of the mammary glands will improve with continued breastfeeding and physical therapy such as hot and cold compresses and massages. However, if the disease progresses to septic mastitis, it must be treated with antibiotics according to the clinician’s instructions, and repeated abscess drainage or incision and drainage surgery will be performed if necessary to cure the disease. This woman has a self-limiting inflammatory disease (i.e., the disease stops after a certain point and gradually recovers). The clinical picture is that of a breast abscess that looks like a malignant tumor and develops into an inflammatory breast lump within a few weeks to a few months, which can only be correctly diagnosed on the basis of a tissue biopsy. Pharmacologic corticosteroid anti-inflammatory therapy is the mainstay of disease management, and surgical excision is used only for drainage of the abscess and removal of the remaining lesion to provide definitive treatment and reduce the risk of recurrence. This case reminds the public that when faced with mastitis that does not improve, it is important to consult a specialist and, if necessary, perform an invasive mammogram in order to diagnose the cause of the disease and effectively cure it.