What should you know about a pea-sized lump under the arm?

The underarm contains hair follicles, sweat glands, skin, and lymph nodes, so a lump can come from more than one structure. Shaving, friction, blocked follicles, or infection may cause tenderness, redness, warmth, or drainage. A deeper lump may feel different from a surface skin lesion. A skin lump is not the same as a diagnosis, and the presence of an underarm lump does not identify its cause. A clinician may examine both underarms and nearby skin, ask about recent infections or vaccinations, and decide whether observation, treatment, or further testing is needed.

Check the area gently rather than repeatedly prodding it. Record when you first noticed it, whether it is changing, whether it moves, and whether there is pain, redness, warmth, discharge, or a skin break. Avoid squeezing, shaving directly over an irritated spot, or applying harsh deodorants until the cause is clearer. Arrange a medical appointment if the lump persists, returns, enlarges, or feels fixed. Treatment, including a [Steroid Injection Into The Skin](/treatments/injectables/intralesional-steroid-injection/), should follow an examination rather than be used to diagnose the lump.

Seek prompt care if the lump becomes rapidly larger, very painful, hot, or surrounded by spreading redness, or if pus, fever, or red streaks appear. A lump that remains, becomes hard or fixed, bleeds, crusts, or breaks the skin needs assessment. Seek urgent help for severe illness, breathing difficulty, or swelling that interferes with swallowing.

Ask whether the lump seems to arise from the skin or deeper tissue, whether the opposite underarm should be checked, and whether it needs monitoring or testing. Ask what symptoms would change the urgency. [Skin Lumps](/symptoms/skin-lumps/) explains the broader symptom, while [Boils](/conditions/boils/) and [Basal Cell Carcinoma](/conditions/basal-cell-carcinoma/) describe conditions a clinician may consider when the examination fits.