Pimple-like lump under the armpit: what to know

A tender surface bump can develop when a hair follicle becomes blocked or irritated, including after shaving, sweating, or friction. A boil may become red, warm, swollen, and filled with pus. Repeated lumps in the armpit or groin can also fit a condition called hidradenitis suppurativa.

An armpit lump can also be a swollen lymph node responding to infection nearby. Breast cancer and lymphoma can involve lymph nodes, but a lump alone cannot identify either condition. Examination is needed to judge its depth, texture, movement, and surrounding skin.

Keep the area clean and dry, avoid squeezing or piercing the lump, and pause shaving or products that sting the skin. A warm, clean compress may ease tenderness. Note when it appeared, whether it grows, and whether similar lumps recur.

Arrange a routine appointment if it does not settle, returns, feels firm or fixed, or comes with breast or chest changes. A clinician may inspect the skin and lymph nodes and decide whether imaging or another test is useful.

Seek same-day medical advice for spreading redness, severe pain, fever, pus with worsening swelling, or feeling faint or unwell. Seek urgent help if swelling affects breathing or swallowing. Do not delay assessment for a hard, growing lump or an armpit lump with unexplained weight loss or night sweats.

Ask whether the lump seems to be in the skin or deeper tissue, what changes to watch for, whether your breast or nearby skin needs checking, and when you should return if it remains.