Bacterial infections of the breast — most commonly mastitis and related breast abscesses (often Staphylococcus aureus) — can cause nipple discharge, usually purulent or bloody. Periductal mastitis/ductitis and, less commonly, fungal infections (Candida) or sexually transmitted infections (e.g., gonorrhea) may also produce discharge. Associated signs include pain, redness, swelling, fever, or foul-smelling fluid; seek medical evaluation.

Nipple sensitivity and leaking can result from hormonal changes (pregnancy, breastfeeding, menstrual cycle, perimenopause), frequent stimulation, certain medications, or elevated prolactin. Infections (mastitis) or benign duct issues may cause discharge. Less commonly, a tumor causes unilateral, bloody discharge. See a clinician if discharge is bloody or from one breast, there’s a new lump, persistent pain, fever, or continuous spontaneous leakage.

Discharge from breast cancer is often spontaneous, persistent, and from a single duct, typically unilateral. It may be bloody or blood-stained, or clear/serous, and sometimes associated with a palpable lump, nipple retraction, or skin changes. Multiple-duct, milky, or bilateral discharge is more likely benign, but any unilateral, bloody, or persistent discharge should be evaluated.

There are three main types of nipple discharge: physiological — usually bilateral, milky (galactorrhea) from pregnancy, breastfeeding or medications/endocrine causes; pathological — spontaneous, unilateral, clear or bloody/serosanguineous discharge often signaling ductal lesions (papilloma) or malignancy; and inflammatory/infective — purulent, green or foul-smelling discharge with pain, redness, duct ectasia or mastitis.

Worry and see a doctor if nipple discharge is spontaneous (not expressed), bloody or clear/watery, from a single duct or one breast, persistent, or occurring in a non‑breastfeeding person. Also seek assessment for an associated breast lump, skin or nipple changes, pain, fever, swollen lymph nodes, or discharge in a man — these signs need clinical evaluation.

See a healthcare provider for diagnosis and an antibiotic prescription (usually oral anti-staphylococcal antibiotics; topical antibiotic ointment may suit superficial infection). Supportive care: warm compresses, regular breastfeeding or milk expression to clear ducts, and analgesics (paracetamol/ibuprofen). An abscess needs specialist assessment and drainage. Seek prompt medical review for fever, worsening pain, spreading redness, or no improvement within 48–72 hours.