Lump on the underside of the breast

The lower breast lies close to the ribs and the fold beneath the breast, so a change may feel superficial or deeper. Common explanations include a blocked skin gland, an irritated hair follicle, a cyst, a fibroadenoma, hormonal breast tissue, or a prominent rib or muscle edge. A breast lump is a common presentation of breast cancer, but a lump alone cannot identify its cause.

Notice whether it is soft or firm, mobile or fixed, tender or painless, and whether it changes with your menstrual cycle. Also look for skin thickening, dimpling, redness, nipple changes, or fluid.

Check the area once in good light and compare it with the other side; repeated pressing can make the tissue sore and harder to judge. Record when you noticed it, its approximate position, any pain, and whether it changes around your period. Arrange a clinical appointment for a new lump that does not settle, even if it is not painful. A clinician may examine the breast and nearby chest wall and decide whether imaging or another test is useful.

Seek prompt medical care for a lump with redness and warmth, fever, rapidly increasing swelling, marked pain, bloody nipple fluid, skin dimpling, a newly pulled-in nipple, or a lump in the armpit. Urgent help is appropriate if severe chest pain, breathlessness, faintness, or sudden illness accompanies the area.

Ask whether the lump feels like breast tissue, a skin lesion, muscle, or rib; what changes would require review; and whether an examination or imaging is appropriate for your age, symptoms, and personal history.