What causes an underarm lump?

The most common cause of an underarm lump is a localized infection in the breast, arm, or the armpit itself, such as folliculitis due to an infected hair follicle. Immune system disorders and some types of cancer, such as breast cancer, can also lead to an underarm lump due to swollen lymph nodes.

Infectious causes of an underarm lump

An underarm lump caused by a bacterial infection can be associated with serious and potentially life-threatening complications if the infection is not treated promptly with antibiotics. Potential infectious causes of an underarm lump include:

  • Abscess (infected pocket of tissue)

  • Bacterial infection, such as a streptococcal or staphylococcal infection

  • Cat scratch fever (bacterial infection from being scratched or bitten by a cat that carries the bacteria)

  • Chickenpox (varicella-zoster virus infection)

  • Folliculitis (infected or inflamed hair follicle)

  • Fungal infection


  • Lymphadenitis (bacterial infection of the lymph nodes)

  • Mastitis (breast tissue infection)

  • Mononucleosis (viral infection)

  • Shingles (varicella-zoster virus infection)

  • Vaccination for various viral diseases, including measles, mumps and rubella

Autoimmune diseases that can cause an underarm lump

An underarm lump can also be caused by diseases in which the immune system attacks healthy tissues in the body (autoimmune diseases) such as:

  • Juvenile rheumatoid arthritis

  • Rheumatoid arthritis (chronic autoimmune disease characterized by joint inflammation)

  • Systemic lupus erythematosus (disorder in which the body attacks its own healthy cells and tissues)

Other noninfectious causes of an underarm lump

An underarm lump can also be caused by noninfectious disorders such as:

  • Allergic reaction

  • Breast tissue that extends into the armpit (this is a relatively common and normal condition)

  • Chronic fatigue syndrome

  • Lipoma (benign, noncancerous growth of fat cells under the skin)

  • Lymphatic obstruction

  • Sebaceous cyst (blocked oil gland)

  • Trauma or bruising of the underarm or shoulder

Cancers that can cause an underarm lump

The most notable life-threatening diseases that can cause an underarm lump, and swollen lymph nodes in general, are different types of cancers including:

  • Hodgkin’s lymphoma (Hodgkin’s disease)

  • Leukemia

  • Metastasized cancer that has traveled to the lymph nodes

  • Non-Hodgkin’s lymphoma

Questions for diagnosing the cause of an underarm lump

To diagnose the underlying cause of a lump under your arm, your doctor or licensed health care practitioner will most likely ask you several questions related to your symptoms. Questions for diagnosing the cause of an underarm lump include:

  • Are you breast-feeding?

  • Are you experiencing any other symptoms, such as a sore throat or fever?

  • Have you noticed any changes in your breast, such as a lump?

  • How long have you had the lump?

  • Is the lump red or painful?

What are the potential complications of an underarm lump?

Viral infections that cause an underarm lump can often be treated with self-care measures at home, and the swelling will go away as your body fights off the infection. Self-care measures include rest and drinking plenty of fluids.

For persistent swelling, redness and pain of an underarm lump, it is important to seek medical care because these are symptoms of a possible bacterial infection. Bacterial infections will need to be treated with antibiotics and the treatment plan designed by your doctor. Left untreated, a localized bacterial infection can spread to the blood and vital organs and become life threatening.

In addition, untreated or poorly controlled lymphoma, leukemia, and other cancers can spread (metastasize) and become fatal. With time, an underarm lump and its underlying cause can lead to serious complications including:

  • Bone infection

  • Meningitis

  • Organ failure

  • Spread of cancer

  • Spread of infection to the blood (septicemia or bacteremia) and septic shock

  • Toxic shock syndrome (caused by the toxin produced by Staphylococcus bacteria)

What is an underarm lump?

An underarm lump generally refers to swelling or enlargement of one of the axillary lymph nodes located under the arm (armpit). Lymph nodes are very small clusters of immune cells that are an important part of the body’s lymphatic system, which is a part of the immune system. Your body relies on the lymphatic system to fight off germs, infections, and abnormal substances, such as cancer cells.<... Read more about underarm lumpintroduction


What other symptoms might occur with an underarm lump?

An underarm lump often occurs with other symptoms that vary in severity depending on the underlying disease, disorder or condition. For example, an underarm lump due to an infectious disease may be sore and painful to touch and occur with a fever and body aches.

Symptoms that may occur along with... Read more about underarm lumpsymptoms

Medical Reviewer: Cynthia Haines, MD Last Annual Review Date: Aug 11, 2013 Copyright: © Copyright 2014 Health Grades, Inc. All rights reserved. May not be reproduced or reprinted without permission from Health Grades, Inc. Use of this information is governed by the HealthGrades User Agreement.

This Article is Filed Under: Allergies and the Immune System