What should you know about a hard lump under the breast?

A lump beneath the breast fold can be a blocked skin gland, inflamed hair follicle, cyst, fatty lump, rib or muscle-related prominence, or a change in breast tissue extending toward the fold. A breast lump is a common presentation of breast cancer, but a lump under the breast is not automatically cancer. Moisture and friction in the fold can also irritate skin and cause a tender, firm area. The surface appearance and whether the lump moves with the skin help guide an examination.

Arrange an appointment if the lump is new, hard, persistent, or difficult to identify. Note whether it sits in the skin crease, breast tissue, or closer to a rib; record pain, redness, drainage, and changes over time. Keep the fold clean and dry, wear comfortable supportive clothing, and avoid squeezing it. A clinician may examine the breast, skin, ribs, and armpit, then recommend imaging if the origin is uncertain. Treatment depends on the cause, so do not apply leftover antibiotics or attempt drainage.

Seek prompt care for spreading redness, warmth, pus, fever, or rapidly increasing pain. Arrange timely review for a lump that grows, stays hard, becomes fixed, causes skin dimpling, changes the nipple, or appears with an armpit swelling. These signs need assessment even when the lump sits below the breast fold.

Ask whether the lump is in the skin, breast, muscle, or chest wall and whether imaging is needed. Ask how to care for the fold, what change would require urgent review, and when you should return if it remains.