What should you know about a small round lump in the armpit?

A tender lump close to the skin can follow shaving irritation, an inflamed hair follicle, a blocked gland, or another local infection. A deeper, mobile lump may be a lymph node reacting to inflammation in the arm, chest, or breast. Breast cancer can present with an armpit lump, and lymphoma can involve lymph nodes, but finding a lump does not diagnose either condition. The side, tenderness, skin changes, and timing all help a clinician interpret it.

Check the area gently rather than repeatedly prodding it. Record when it appeared, whether it changes, and any recent skin injury, infection, vaccination, or breast change. Arrange an appointment if it remains, enlarges, feels firm or fixed, or has no obvious explanation. Examination may include the armpit, breast or chest wall, arm, and nearby skin; further testing depends on those findings.

Seek urgent care for severe pain, rapidly spreading redness, significant swelling, fever with marked illness, or difficulty breathing. Arrange timely review for a persistent or enlarging lump, a new breast or chest change, nipple discharge, unexplained weight loss, drenching night sweats, or several swollen areas.

Ask whether the lump seems skin-based or nodal, what features make follow-up necessary, and whether an ultrasound or other examination is suitable. Mention any breast, arm, chest, skin, or general symptoms, even if they seem unrelated.