Inflammation of the breast. Acute mastitis, usually caused by bacteria, begins almost exclusively in the first three weeks of nursing and can be cured with antibiotics without stopping nursing. The breasts may become swollen, red, hard, and tender; without treatment abscesses may occur. Mastitis can be localized or widespread, and the breast's lymphatic system may be involved. Girls may have brief hormone-induced breast inflammation soon after birth and during puberty. Chronic mastitis usually occurs in systemic diseases (e.g., tuberculosis, syphilis). One rare type is seen mostly in older women with a history of difficult nursing. Some mastitis cases resemble certain cancers.