Small lump under the breast: what to know

The crease beneath the breast contains skin, sweat glands, fatty tissue and the chest wall; breast tissue may extend close to this area. A blocked skin gland, boil, irritated hair follicle, cyst, lipoma, muscle edge or breast lump can feel like a small swelling. Breast cancer commonly presents as a new breast lump, but the position beneath the breast does not establish a cancer diagnosis.

Heat, friction, moisture and tight clothing can irritate the fold. A tender red lump may reflect inflammation, while a deeper firm or persistent lump needs assessment even when the skin looks normal.

Arrange a clinician review for a new lump that persists, enlarges or is difficult to locate. Note whether it is on the skin or deeper, and whether it changes with your cycle, movement or pressure. Keep the fold clean and dry, choose breathable clothing and avoid squeezing, lancing or applying harsh products. Mention breastfeeding, recent shaving, skin problems, injury and any nipple or breast changes.

Seek prompt care for increasing redness, warmth, swelling, pus, fever or worsening pain, as these can signal an infection. A hard or fixed lump, rapid growth, skin dimpling, nipple inversion, bloody discharge or an underarm lump also deserves prompt assessment. Seek urgent help if you feel faint, severely unwell or the redness is spreading.

Ask whether the lump is in the skin, breast tissue or chest wall, whether it needs ultrasound or another test, and how to care for the fold while waiting. Clarify which changes should prompt an earlier review.