Why Is My Armpit Swollen?

Medically Reviewed By Angelica Balingit, MD
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The lymphatic system in your body filters foreign substances and stores lymphocytes, also called white blood cells. As part of your immune system, lymphocytes fight diseases. In the lymphatic system are hundreds of lymph nodes, which are small round clusters of cells. They trap germs and abnormal cells, activating immune responses that rid the body of potential infections.

As lymph nodes are in your armpit amongst other places, swelling in your armpit can indicate that your body is responding to a disease or infection. These can be many different diseases, ranging from common colds to serious illnesses such as lymphoma.

This article will explain what could cause swelling in the armpit. It will also describe other symptoms that may occur with it and when to seek medical care.

What is swelling in the armpit?

woman showing armpit
Lucas Ottone/Stocksy United

Swelling in the armpit can show that your body is responding to an infection. Lymph nodes are part of the body’s disease-fighting immune system. These nodes are small, bean-shaped clusters located all around the body, including:

  • neck
  • armpit
  • chest
  • abdomen
  • groin

Swelling in the armpit can feel like a discrete lump rather than diffuse swelling across the entire area.

The medical name for the armpit is axilla, so another name for this symptom is axillary swelling. You may or may not have other symptoms alongside a swollen armpit.

When to contact a doctor

There are various possible causes for armpit swelling. Some of these causes are more concerning than others.

Because a swollen underarm can indicate a potentially serious issue, it is important to see your doctor for a diagnosis.

You should contact your doctor if an underarm lump:

  • does not go away within a couple of weeks
  • gets bigger
  • is hard and fixed, meaning you cannot move it around within the tissue
  • is not painful

Seek medical care if an underarm lump accompanies other symptoms such as:

  • fever
  • night sweats
  • unexplained weight loss
  • redness around the lump
  • pain in other places around the body

What causes a swollen armpit?

swollen armpit
Alexandr Serebrynnikov/Shutterstock

There are several possible reasons for your armpit to swell up. One of the most common reasons is a swollen lymph node.

Swollen lymph nodes

You have several lymph nodes in each armpit. Some of them are close to the skin, while others are deeper. They act as filters for the lymph system in your upper body. When your immune system starts fighting an infection, the lymph nodes help trap viruses, bacteria, and other cells.

Usually, this means the lymph nodes on both sides of your body swell, including those under your arm and in your neck. Bilateral lymphadenopathy is the name of this condition. It is a typical response to an infectious disease or infection.

A swollen lymph node on one side is unilateral axillary lymphadenopathy.

Breast infections

Swollen lymph nodes on one side can also indicate a breast infection such as mastitis. Mastitis is an infection and inflammation of the breast, causing redness, swelling, and pain.

Local infections of the arm

Arm or underarm infections can also cause a swollen lymph node. Cat scratch disease is an example of this, in which bacteria from a scratch caused by a feline can result in swollen lymph nodes, headache, and fever.

An abscess, a collection of pus under the skin formed from an infection or trapped foreign object, can also cause swelling in the armpit.

Read more about abscesses here.

Autoimmune diseases

Autoimmune diseases may cause swelling in the armpit. Lupus, particularly systemic lupus erythematosus, is a long-term autoimmune condition that causes tiredness, rashes, and joint pain. Lupus may cause swollen lymph nodes.

Rheumatoid arthritis (RA) can also cause armpit swelling. RA is an autoimmune disorder in which your immune system mistakenly attacks the joint lining. This condition can cause pain, stiffness, and tenderness in the joints.

Studies show that RA affects the lymph nodes when the capacity to drain fluid from inflamed joints reduces, leading to inflamed lymph nodes.

Scleroderma is another autoimmune condition that causes the tightening and hardening of the skin. A symptom of scleroderma may be swelling in the armpit.

Read more about autoimmune conditions here.

Viral infections

The most common type of viral infection is the common cold. Viruses diseases are contagious and can result in several symptoms, such as:

Viral infections such as glandular fever, also known as mononucleosis, can often cause swelling in the armpit.

HIV is a more serious virus that can cause swelling in the armpits. It gradually weakens the immune system over time. One of the first signs of HIV is swollen lymph nodes.

Read more about viral infections here.


A swollen lymph node on one side can indicate advanced breast cancer. Lymph nodes under the arm are common places for breast cancer to spread.

Other types of cancer that can cause swelling in the armpit are:

  • Lymphoma: This is a group of blood cancers that start in the lymph nodes or bone marrow. A symptom is swollen lymph nodes that can appear in the armpit, groin, or neck.
  • Leukemia: This is a type of cancer of the white blood cells that help fight infection. Symptoms include swollen lymph nodes.
  • Thyroid cancer: Cancer of the thyroid can also cause swelling in the armpit, although swelling in the neck is usually noticed first.

Read all about cancer here.


Sarcoidosis is a condition in which groups of cells in your immune system form lumps, called granulomas, in various organs in the body. Depending on the organs involved, swelling in the lymph nodes, including the armpits, can occur.

Other causes for swollen armpits

  • Cysts, which can develop around hair follicles or oil-producing glands
  • Hidradenitis suppurativa, a chronic skin disease with recurrent boil-like lumps
  • Lipomas, soft, painless, benign tumors of fat cells

Seeing your doctor is the only way to know for sure what is causing an armpit lump or swelling. The sooner you seek medical care and any necessary treatment, the better the outcome is likely to be.

What other symptoms might occur with a swollen armpit?

Some armpit lumps have no other symptoms, are painless, and do not cause any discomfort. However, people often notice additional symptoms along with swelling. These symptoms can include:

These symptoms can occur on one side or both, depending on the cause. It is important to see your doctor whether or not you have these other symptoms. Your doctor should evaluate even a painless lump or swelling without other symptoms.

How is armpit swelling treated?

Treatment for armpit swelling will depend on the underlying cause. Ignoring the lump or swelling can lead to more problems and possibly more intensive treatments, so it is best to seek medical care as soon as you can.

What are the potential complications of armpit swelling?

The possible complications from armpit swelling depend on the cause of the swelling. Your doctor will want to know about all your symptoms and will perform a physical exam. You may also need imaging tests or lab tests to help your doctor diagnose the cause. Getting a timely diagnosis offers the best chance of treatment success.


Swelling in your armpit can indicate that your body is responding to a disease or infection. These can be many different diseases, ranging from common viral infections such as a cold to serious illnesses such as cancer.

It is best to seek medical advice as soon as possible to have the best chance of treatment success for armpit swelling.

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Medical Reviewer: Angelica Balingit, MD
Last Review Date: 2022 Apr 24
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