Lump Under the Armpit: Should I Worry?

Written By: Dana-Farber Editorial Team
Medically Reviewed By: Adrienne Waks, MD

Key Takeaways:
• Most of the time, a lump under the armpit is the result of an enlarged lymph node. This means that body’s immune system is responding to a small issue such as an infection or irritation.
• In rare circumstances, an enlarged lymph node that has certain characteristics can be a sign of cancer.
• Regardless of the features of the lump or the symptoms accompanying it, if it does not resolve on its own, it is a good idea to have it checked out by a doctor.

Is it normal to have a lump in the armpit?

A lump in the armpit is usually not something to worry about, and the explanation for it is usually something mild and relatively harmless.

Will a lump in the armpit go away? When should I see a doctor?

In many cases, lumps under the armpit are caused by a swollen lymph node — in other words, the body’s immune system responding to a small issue such as an infection or irritation. In many cases, a lump in the armpit will go away quickly.

However, you should get an armpit lump checked by your doctor if the lump persists for more than a week. This is especially true if the lump is accompanied by other symptoms such as:

  • persistent fever
  • night sweats
  • unexplained weight loss

Other reasons to seek medical attention are if the lump is beneath rather than in the skin, continues to get larger, and there is no redness to indicate infection.

What can cause an armpit lump?

There are many potential causes of a lump in the armpit, and in most cases, the lump will go away on its own.

Potential causes include:

  • Infection: In many cases, a lymph node will swell because it’s fighting an infection somewhere in your body, which is part of the normal function of the lymph nodes. This is an indication that your lymphatic system is working properly.
  • Skin irritation: Another common explanation of an armpit lump is that something has irritated the skin. This might be a skin cyst (a fluid-filled sac beneath the skin) or a blocked hair follicle that becomes inflamed. In most cases, these will resolve on their own.
  • Allergy: An allergic reaction to deodorant, soap, or some other substance can also cause a lump in the armpits.
  • Autoimmune disorders: Autoimmune disorders such as Lupus, as well as others, can trigger the immune system and cause the lymph nodes to swell.
  • Cancer: In rare circumstances, an enlarged lymph node can be a sign of cancer. Since it is difficult to tell the difference between a cancerous node and one that is benign, it’s prudent to see your doctor if the issue persists. Lymphoma is caused by alterations in the white blood cells (infection fighting cells), which causes them to grow and multiply faster than normal. There are several different types of lymphoma, and treatment varies by type. Swollen lymph nodes in the armpit can also be caused by other forms of cancer, including breast cancer, and other types of cancer that have metastasized to the lymph nodes.

How can you tell if an armpit lump is cancerous? Are cancerous lumps painful?

A painful lump in the armpit can potentially be cancerous, but usually when a lump is painful or tender, there is another cause. Infection or inflammation tend to cause pain and tenderness, whereas cancer is less likely to be painful. A lump in the armpit tends to be more concerning if it is painless.

A normal lymph node should have the shape of a lima bean and be firm while still having some give to it. A cancerous lymph node will often (but not always) become rock-hard and change shape to resemble a marble rather than a lima bean.

If a swollen lymph node is overly firm and is not shaped like a lima bean, it could potentially be cancerous. Likewise, if the lump is obviously not in the skin, and if it persists, gets larger, and is not accompanied by signs of an infection, it may be time to seek medical attention.

Vaccines and armpit lumps

Common vaccines, such as those for the flu or COVID-19, can occasionally trigger the immune system and cause the lymph nodes in your armpit to swell. This is normal and not a cause for concern. However, if the armpit lumps persist for more than a few weeks after the shot, then you should bring them to the attention of your doctor.

What if my armpit lump turns out to be cancer?

In the rare case that an armpit lump turns out to be a cancerous tumor, there are many different types of treatment. Possibilities include:

What is the function of lymph nodes?

The lymph nodes are part of a lymphatic system that filters germs, infections, and cancer cells out of your body. The nodes are found in many parts of your body (neck, armpit, chest, abdomen, groin) and are connected by a network of tiny fluid-filled tubes similar to your blood circulatory system.

About the Medical Reviewer

Adrienne Waks, MD

Dr. Waks received her undergraduate degree from Princeton University in 2006 and her MD degree from Harvard Medical School in 2011. She completed residency training in internal medicine at Brigham and Women's Hospital, where she subsequently served an additional year as a Chief Resident in Internal Medicine. She completed fellowship training in medical oncology at Dana-Farber/Partners CancerCare, then joined the staff of the Breast Oncology Center at Dana-Farber Cancer Institute.

1 thought on “Lump Under the Armpit: Should I Worry?”

  1. You describe exactly how my breast cancer was discovered. It was a long process to finally get to the breast cancer diagnosis. I had never seen or read of anyone with a similar situation. Good information. Thank you.

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