If you have an armpit lump and you want to narrow down the possible causes you can think of the following:

1. Is the lump painful?

Painful lumps are usually caused by infections. Lumps from cysts, benign tumors and cancers are usually painless.

2. Is the overlying skin changed?

Red skin overlying a lump suggests a bacterial infection. Red skin without lumps can also appear in fungal infections (ringworm), allergic reactions (dermatitis) and psoriasis.

3. Did a lump appear suddenly or slowly?

A lump that appears overnight is probably caused by an infection. Slowly growing lumps suggests a chronic infection, cyst, benign tumor or cancer.

4. Do you have any other symptoms?

  • Sudden fever suggests an infection.
  • Slowly developing low-grade fever and unintentional weight loss suggest a lymphoma.
  • Skin rash all over the body occurs in infectious mononucleosis.

Causes of Armpit Lumps

Causes of underarm lumps include:

1. Cysts and benign tumors:

  • sebaceous cyst
  • lipoma

2. Infections:

  • local armpit infections, such as boils and hidradenitis suppurativa
  • arm infections, such as cellulitis and lymphagitis
  • systemic infections, such as infectious mononucleosis, HIV/AIDS, bubonic plague and rat bite fever

3. Cancers:

  • breast cancer
  • lymphoma
  • leukemia

Cysts and Benign Tumors

Sebaceous Cyst

Sebaceous cyst is a clogged sebaceous gland filled with a greasy material. It appears as a soft painless lump with normal overlying skin. It has a small opening, through which you can squeeze the greasy material out, but the cyst usually recurs.


Lipoma is a benign tumor composed of fat tissue. It appears as a painless soft lump, which can be as small as a marble or as big as a golf ball. The overlying skin is normal and there is no opening in it.

Lipoma grows slowly and does not spread to other tissues. If necessary, it can be surgically removed.



A boil or furuncle is a bacterial infection of several adjacent hair follicles. It appears as a tender red bump with a white or black head or crust on top. It may ooze yellow fluid or white pus.

Do not squeeze the pus out of a boil, because you may spread the infection to the nearby skin.

Boils can heal on their own in few weeks. An ointment that contains the antibiotic mupirocin can speed up the healing. Large boils can be treated with oral antibiotics.

Boil or furuncleCredit: https://en.wikipedia.org/wiki/Abscess

Hidradenitis Suppurativa

Hidradenitis suppurativa is a chronic bacterial infection of the underskin tissues in the armpit. Overweight individuals are at increased risk.

Symptoms include one or more red lumps or ulcers that can ooze fluid and eventually scar over.

Treatment can include topical or oral antibiotics, draining or surgical removal of the affected armpit tissue.

Hidradenitis suppurativaCredit: http://www.omicsonline.org/ireland/hidradenitis-suppurativa-peer-reviewed-pdf-ppt-articles/

Arm Infections

An arm infection, such as cellulitis and lymphangitis, can spread into the armpit lymph nodes that can become swollen, red and painful.

Cellulitis is a bacterial infection of the underskin tissues that appears as a thick red patch in an arm.

Lymphangitis is an inflammation of the lymphatic vessels. It can be caused by a snake bite or skin cut. A typical symptom is a tender red stripe that travels from the cut along the arm toward the armpit.

LymphangitisCredit: http://www.wikihow.com/Check-a-Wound-for-Infection

Infectious Mononucleosis

Infectious mononucleosis is a viral infection that occurs mainly in children and young adults.

Painful and enlarged lymph nodes can appear in the armpits, under the chin, in the neck and groin, usually on both sides.

Other symptoms, which can last for more than a month, include fever, sweating, fatigue, red skin rash and sore throat. Lumps in the armpits may persist for several months.

Other systemic infections with enlarged underarm lymph nodes:

  • chronic malaria
  • toxoplasmosis
  • plague
  • HIV/AIDS (see the picture below)
Enlarged axillary lymph nodesCredit: http://aids.about.com

Breast Cancer

Breast cancer usually appears as a firm nodule in a breast. The cancer can spread into the lymph nodes above and below the clavicle and in the armpit on the affected side. Enlarged nodes are usually not visible but can be detected with the fingers by deep palpation. They may cause discomfort but are typically not painful or tender to touch.

Breast cancerCredit: http://fair.org/extra/overlooking-evidence/attachment/breast-cancer-flickr-tipstimes/


Lymphoma is a type of cancer in which white blood cells overgrow in the lymph nodes. It can cause soft, painless lumps in the armpits, neck and groin on both sides (see the picture below).

A typical symptom is an armpit pain triggered by drinking even a small amount of alcohol.

Other symptoms can include low-grade fever, night sweats and loss of appetite.

Leukemia and other blood malignancies can also present with enlarged lymph nodes.

Enlarged lymph nodesCredit: http://www.wikihow.com/Check-Lymph-Nodes

Other Causes of Lymph Node Enlargement

In rheumatoid arthritis and systemic lupus erythematosus, lymph nodes in the armpits, neck and groin on both sides can become enlarged but usually remain painless.

Other symptoms of rheumatoid arthritis include pain and swelling in the fingers, wrists, shoulders, knees or hips.

All images in this article are under Creative Commons licence.