Small lump under the skin in the armpit: what to know

The armpit contains hair follicles, sweat glands, fat, muscles, and lymph nodes that drain the arm, chest, and breast area. Shaving irritation, an ingrown hair, a boil, or a blocked gland may cause a tender surface lump. A lymph node can enlarge while responding to infection or inflammation nearby. Breast cancer and lymphoma are also conditions a clinician may consider when a lump persists, is firm, or occurs with other changes. The lump itself cannot identify its cause.

Observe without squeezing, piercing, or applying irritating products. Note whether the lump is in the skin or deeper, and record tenderness, redness, warmth, drainage, growth, or a recent cut, vaccine, infection, or breast change. Arrange an appointment if it remains, recurs, enlarges, or has no clear skin explanation. The clinician may examine both armpits, the breast or chest, and nearby arm skin, then decide whether imaging or another test is useful.

Get prompt help for rapidly spreading redness, severe pain, high fever, or feeling acutely unwell. Arrange timely review for a hard or fixed lump, a lump that keeps growing, nipple or breast changes, persistent breast pain, unexplained night sweats, or unexplained weight loss. These findings need evaluation and do not prove that the lump is cancer.

Ask whether the lump appears to be in the skin or a lymph node, whether a nearby infection explains it, and whether the breast or chest needs examination. Ask which changes require faster review and whether imaging or sampling is appropriate.