An armpit lump refers to enlargement of one or more lymph nodes under the arm.

Lumps in the armpit have various causes. Cysts and infections on the surface of the skin of the armpit may be caused by shaving or use of antiperspirants (as opposed to deodorants). This occurs most frequently in adolescents just beginning to shave. Abscesses under the skin may also produce large, painful lumps in the armpit.

Lumps may occur when lymph nodes are swollen due to bacterial or viral infections, vaccinations, and cancer.

Lymph nodes are filters that can catch infectious organisms or cancerous tumor cells. When they do, lymph nodes increase in size and are easily felt. A breast self-examination should always include the armpit because breast cancer can enlarge the armpit lymph nodes even when the breast itself seems perfectly normal.

• Bacterial infection
  • Arm or breast infection
  • Cat scratch disease
  • Ascending lymphangitis
  • Lymphadenitis
• Cancer
  • Hodgkin's lymphoma
  • Leukemia
  • Non-Hodgkin's lymphoma
• Fungal
  • Sporotrichosis
• Other
  • Benign (harmless) cyst
  • Lipomas (harmless fatty growths)
  • Normal breast tissue (breast tissue extends into the armpit area)
• Vaccinations
  • Allergic reaction possibly caused by sulfa drugs, iodine, or penicillin
  • Measles, mumps, rubella vaccine (rare)
  • Smallpox vaccination
  • Typhoid vaccine
• Viral infection
  • AIDS
  • Chickenpox
  • Infectious mononucleosis
  • Shingles (herpes zoster)

Home care depends on the reason for the lump. Check with your health care provider to determine the cause.

Call if you have any unexplained armpit lumps. Do not try to diagnose lumps without professional help.

Your doctor will perform a physical examination and ask questions about your medical history and symptom, such as:

• When did you first notice the lump?
• Is it getting better, worse, or staying the same?
• Are you breast-feeding?
• Have you noticed any factors that make it worse?
• What other symptoms are also present?
• Is the lump painful?

The physical examination may include palpation -- gently pressing the nodes with the fingertips.

Testing depends on what is found during the physical examination. Tests that may be done include:

• Blood tests, such as a complete blood count (CBC)
• Kidney function tests
• Liver function tests
• Liver-spleen scan
• Lymph node biopsy
• Mammogram
• Platelet count
• X-ray of the chest

OUTLOOK

A lump in the armpit caused by a generalized viral infection will eventually disappear without treatment. A lump in the armpit caused by an allergic reaction will go away after the "trigger" is removed. No treatment is necessary for a lump in the armpit caused by normal breast tissue. Usually, no treatment is necessary for a cyst.

A lump in the armpit caused by a lipoma is harmless, unless it grows so large that it causes discomfort.

The outlook for cancerous lumps depends on the specific type of cancer. See the following for more information:

• Breast cancer
• Hodgkin's lymphoma
• Non-Hodgkin's lymphome
• Leukemia

Oguz A, Karadeniz C, Temel EA Citak EC, Okur FV. Evaluation of peripheral lymphadenopathy in children. Pediatr Hematol Oncol. 2006;23(7):549-561.

Zakaria S, Johnson R, Pockaj BA, Degnim AC. Breast cancer presenting as unilateral arm edema. J Gen Intern Med. 2007; 22(5):675-676.

Henry PH, Longo DL. Enlargement of lymph nodes and spleen. In: Kasper DL, Braunwald E, Anthony S. Fauci AS, eds. Harrison’s Internal Medicine. 16th ed. New York, NY: McGraw-Hill; 2005.