Lump in Armpit: Common Causes & What to Do

Medical review: Dr. Clarisse Bezerra
Family Doctor
June 2022
  1. Folliculitis
  2. Boil
  3. 3. Hidradenitis suppurativa
  4. Sebaceous cyst
  5. Swollen lymph node

In most cases, a lump in the armpit is not concerning and is easy to treat, therefore you should not be worried if one appears. Some common causes include a boil, inflammation of a hair follicle or a swollen lymph node. 

Nonetheless, in some cases, it may be a sign of a skin issue, like acne inversa. In rare cases ,it may be a sign of an immune disease, infection or even cancer. Cancer is only suspected if lumps grow over time or if they are accompanied by symptoms like fever, weight loss or night sweats. 

To determine the cause of a lump in the armpit, you should see your family doctor or dermatologist to evaluate the area and order testing as needed to identify a cause. 

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1. Folliculitis

Folliculitis is an inflammation of the hair follicle which can be caused by a local bacterial, fungal or viral infection. It can also occur if the hair becomes ingrown. Folliculitis can cause many small pimples which can be painful, red or even yellow due to the presence o pus. This rash can also be itchy. 

What to do: After a medical evaluation, the doctor may prescribe anti-inflammatory medication to reduce discomfort and antibiotics to fight the infection. This medication may be topical or oral. The doctor may also recommend you to prevent any irritation or scraping of the infected skin until the inflammation improves. 

To prevent folliculitis, you should keep the skin clean, dry and hydrated. Learn more about the treatment of folliculitis

2. Boil

A boil, or furuncle, is also caused by a follicular infection. However it is much deeper and also causes swelling in the skin surrounding it. The itching is more intense, more red, and produces much more pus. 

What to do: You should seek medical attention for assessment of the area and to indicate whether the boil should be drained. The doctor may order oral or topical antibiotics and advise you to apply warm compresses to speed up healing. While treating a boil, you should prevent new infections by using an antiseptic soap. Wash the area daily with this soap and be sure to wash any clothes that came in contact with the boil in hot water. 

3. Hidradenitis suppurativa

Hidradenitis suppurativa in the armpit is an inflammation of the sweat glands that is caused by blockage of the glands. It leads to the formation of painful lumps that can scar the skin. 

What to do: This condition,nwhich is also referred to as acne inversa, should be assessed by a doctor or dermatologist, who will prescribe treatments to reduce irritation in the affected area. Medications may include antibiotics or steroid infections. In severe cases, surgery may be necessary to remove the affected skin, which is then replaced with a graft. 

Keep the area with hidradenitis suppurativa clean and avoid using tight clothes. Warm compresses on the area can also help treatment. 

4. Sebaceous cyst

A sebaceous cyst is a type of lump that appears under the skin that contains accumulated sebum. It can appear anywhere on the body and is generally not painful, unless it becomes inflamed or infected (in which case, it can become painful, hot and red). 

What to do: Treatment is indicated by a doctor or dermatologist, who may recommended warm compresses or use of anti-inflammatories. In some cases, a small procedure may be necessary to remove it.

5. Swollen lymph node

A swollen lymph node can occur due to inflammation or infection that occurs in the arm, chest or breat. The lymph node is a component of the immune system, and it can increase in size to produce more defense cells, which will help to attack any foreign invaders that can compromise the body. 

In most cases, swollen lymph nodes are not concerning and can occur for many reasons, like an ingrown hair, folliculitis, a boil, lymphadenitis, but it can also indicate a systemic illness, like auto-immune disease or cancer (which mainly occurs when lumps grow quickly or are found in various parts of the body).

The main causes of swollen lymph nodes include:

  • Inflammation or infection within hair follicles
  • Infections like sporotrichosis, brucellosis, or cat scratch disease, among others 
  • Autoimmune disease like lupus, rheumatoid arthritis, dermatomyositis or sarcoidosis
  • Cancer, like breast cancer, lymphoma or leukemia 

Lymph nodes that are concerning will be large (over 2.5cm in diameter in diameter), hard, fixed, and last for over 30 days. These lumps are often accompanied by symptoms like fever, weight loss, or night sweats and can appear in many areas of the body. 

What to do: Generally, swollen lymph nodes will disappear on their own within a few days to weeks. The doctor may be able to confirm whether it is a swollen lymph nodes and will determine whether further testing is necessary. Learn more about the causes of swollen lymph nodes

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Edited by Tua Saude editing team in June 2022. Medical review completed by Dr. Clarisse Bezerra - Family Doctor in May 2022.
Medical review:
Dr. Clarisse Bezerra
Family Doctor
Dr. Bezerra possesses a medical degree and specializes in family medicine. She is licensed to practice under CRM-CE licence #16976.