Why does only one breast hurt?

Bottom linePain in just one breast usually comes from the chest wall (rib cartilage or muscle), a cyst, mastitis, injury, or bra fit rather than the breast tissue itself, and hormonal soreness is often worse on one side; get it checked if it stays fixed in one spot beyond a cycle or two or comes with a lump, redness, skin changes, or fever.

One-sided breast pain usually has a local, benign cause - and it is one of the most searched breast symptoms, so you are in good company wondering about it.

Common causes of pain in one breast

• Chest wall pain - the most frequent culprit. Costochondritis (inflamed rib cartilage), a pulled pectoral muscle, or poor posture cause sharp, well-localized pain that feels like it is in the breast but actually sits beneath it. It typically worsens when you press on the spot, move, or breathe deeply.
• A breast cyst - a fluid-filled sac that can appear in one breast, ache or feel tender, and often swells before your period
• Mastitis or an abscess - a painful, hot, red area, often with fever; most common while breastfeeding but possible anytime. Needs prompt treatment.
• Injury or strain - workouts, carrying, a knock you barely registered
• Bra fit - an underwire pressing on one side
• Referred pain - pain under the left breast in particular can come from the stomach (reflux, gastritis) or, rarely, the heart; under the right, from the gallbladder

Cyclical pain can be lopsided too

Hormonal tenderness is usually in both breasts, but it is often worse on one side, so a monthly pattern still points to hormones even if one breast complains louder.

When to get it checked

See a doctor if the pain is fixed in one spot and persists past a cycle or two, or comes with a new lump, skin dimpling, redness, nipple discharge, or fever. Seek urgent care for left-sided chest pain with exertion, breathlessness, or arm or jaw pain - that pattern needs a heart check first, not a breast check.

One-sided pain alone is rarely cancer - early breast cancer is usually painless - but persistent localized symptoms always earn a clinical exam. A self-check can tell you whether there is a lump to report; it cannot rule anything out.

Related: why do my breasts hurt · what does a breast lump feel like