Swollen lymph nodes in the armpit can be caused by local inflammation or infections, like folliculitis, boils or lymphadenitis. Lymph node swelling is usually caused by an immune system response, which is stimulated to fight a possible viral, fungal or bacterial infection. However, it can also occur due to an autoimmune disease, a vaccine reaction or even cancer.

Depending on the underlying cause a swollen lymph node in the armpit (which is also referred to axillary lymphadenopathy), symptoms like fever, sensitivity to touch, night sweats, weight loss for no apparent reason and swollen lymph nodes in other areas of the body can also emerge.

It is important to see a doctor if the swollen lymph node in the underarm does not resolve, if it continues to increase in size, or if you experience other symptoms. The doctor will perform an assessment to identify the cause and start treatment as appropriate.

What causes swollen lymph nodes in the armpit?

The main causes of lymph node swelling in the underarm are:

1. Folliculitis

Folliculitis is an inflammation of the hair follicle, which makes it difficult for the follicle to penetrate the outermost later of skin. It causes symptoms like one or many small pimples in the arm pit which can be painful, red (or yellow if pus is present), itchiness and swollen lymph nodes in the armpit.

Folliculitis in the armpit, also known as an ingrown hair, is a relatively common finding that is caused by removing hair with a razer or waxing. It can also occur as a result of a bacterial infection (from Staphylococcus aureus or Pseudomonas aeruginosa bacteria) or a fungal infection (like Malassezia fungus).

What to do: You should cleanse the armpit with antiseptic soap and apply warm compresses on the area to reduce skin irritation and discomfort. The doctor may prescribe anti-inflammatories, creams, ointments or antibiotics to treat any infection. It is important to avoid scraping the skin or performing any hair removal until the inflammation has improved.

Read more about folliculitis treatment, which may involve medications, ointments and even home remedies.

2. Hidradenitis suppurativa

A swollen lymph node in the armpit may occur due to hidradenitis suppurativa, which is an inflammation of the sweat glands that is caused by an obstruction within the gland. It causes hard, painful lumps, red skin, burning and excessive sweat.

This type of inflammation can be caused gy genetic mutations, a weakened immune system or lifestyle habits like smoking, or obesity.

What to do: You should see a dermatologist for symptom management with antibiotic creams or corticosteroid injections in the armpit. More serious cases may require surgical removal of the affected area.

Patients are also advised to keep the area clean, to avoid using tight clothing and to apply warm compresses to the armpit to help speed-up recovery.

3. Lymphadenitis

A swollen lymph node may occur due to lymphadenitis, which is an inflammation of the lymph nodes in the armpit. Swelling is usually caused by a viral, bacteria, fungal or protozoan infection.

This condition is associated with symptoms like fever, pain in the affected area, and swollen lymph nodes in other areas of the body (like the neck). Other swollen lymph nodes are especially common with systemic infections, like mononucleosis or cytomegalovirus.

What to do: You should consult a family doctor for assessment to determine the underlying cause of the swollen lymph nodes, and treatment (which may involve antibiotics or anti-inflammatories).

4. Vaccination

Some vaccines, like the BCG vaccine, flu shot, chicken pox vaccine, mumps vaccine or shingles vaccine, can stimulate lymph node swelling in the areas around the injection site. This is an immune response to the vaccine that leads to the production of antibodies.

The COVID-19 vaccine can also lead to swollen lymph nodes in the armpit as a side effect. Learn more about other possible side effects from the COVID-19 vaccine and how to treat them.

What to do: Generally, swollen lymph nodes from vaccination resolve within 3 to 4 weeks, without any targeted treatment. If the lymph nodes do not improve or if they continue to grow, you should see a doctor for assessment. The doctor may order tests like an X-ray, CT scan or MRI to identify what is causing the swelling.

5. Boils

A boil is an infection of the hair follicle root, which in most cases is caused by Staphylococcus aureus bacteria. This bacteria is naturally found on the skin and mucosas, but overgrowth can lead to a hard lump that gradually grows and causes pain, head in the area, redness and sensitivity to touch. It can also lead to a swollen lymph node, as the immune system activates to fight the infection.

What to do: Patients can apply a warm compress on the boil 3 times per day, and are advised to also wash the area with warm water and a mild soap. You should not pop the boil, as this can worsen swelling and infection and make it more difficulty to treat. In some cases, the doctor may recommend draining of the boil (which consists of removing the accumulated pus) as well as antibiotic treatment.

Learn more about how to get rid of a boil fast.

6. Infection

Some infections, like HIV or mononucleosis, can stimulate lymph nodes and lead to swelling in the armpit and other parts of the body, like the front and back of the neck.

What to do: You should see a family doctor or infectious disease specialist to diagnose the type of infection present and initiate appropriate treatment. The doctor may prescribe antiretrovirals for hIV or use analgesics or anti-inflammatories to reduce symptoms like swollen lymph nodes and fever, which are common with mononucleosis.

7. Autoimmune disease

Autoimmune diseases, like lupus or rheumatoid arthritis, significantly affect the immune system. Defense cells can start to accumulate within the lymphatic ganglions, leading to swollen and reactive lymph nodes.

In these cases, swollen lymph nodes can appear in many parts of the body in addition to the arm pit. It is also common for patients with an autoimmune disease to report muscular pain, nausea, vomiting and night sweats.

What to do: If you suspect you may have an autoimmune disease, you should see a family doctor or rheumatologist for testing and treatment as necessary. Read more about the most common autoimmune diseases and how they are treated.

8. Ganglionic tuberculosis

Ganglionic tuberculosis is an infectious disease caused by the Mycobacterium tuberculosis bacteria. It can cause swollen lymph nodes in the arm pit, as well as other areas of the body, like the neck, chest or groin.

This type of tuberculosis is more common in patients infected with HIV and in women between the ages of 20 and 40.

What to do: You should consult an infectious disease specialist or family doctor for treatment, which usually involves antibiotics (like rifampicin, isoniazid or pyrazinamide) for at least 6 months.

9. Lymphoma

A swollen lymph node in the armpit may emerge as a result of lymphoma, which is a type of cancer that affects the lymph nodes. It causes hard lump in the armpit that does not resolve within a month or two and continues to grow.

Generally, this type of cancer is also associated with symptoms like swollen lymph nodes in the groin, fever, night sweats, fatigue and weight loss for no apparent reason.

What to do: You should see a family doctor, hematologist or oncologist for testing, like bloodwork, CT scan or a PET scan. These will help to identify the type of lymphoma present and will guide treatment, which may involve chemotherapy or radiation therapy.

10. Breast cancer

Breast cancer is one of the most common types of cancers that affect women, although it can also be diagnosed in men. Patients are often asymptomatic in the initial phases of breast cancer, however the main sign of it is the presence of a tumor or hard nodule in the breast.

Other symptoms that may emerge include, swelling, reactive lymph nodes in the armpits, pain that radiates to the arm, redness, nipple discharge and tender breasts.

What to do: If you notice any breast changes, you should consult a doctor for assessment. If confirmed, the doctor will initiate treatment, which may involve surgery, chemotherapy, or hormone replacement therapy.

Breast cancer can be cured, depending on the type and stage of cancer. Prevention is very important and patients are advised to regularly self-assess and adhere to routine mammogram screening.

When to see a doctor

You should see a family doctor or infectious disease specialist if you notice a swollen lymph node in the armpit within the following contexts:

The swollen lymph node does not improve within 2 weeks
The lymph node grows over time
Redness, pus or lumps in the armpit
Painful lymph nodes
Lymph nodes in other areas of the body
Hard lymph nodes that are fixed and hard
Lymph nodes that measure for 2.5 cm (about 1 inch) in diameter
Fever
Night sweats
Weight loss for no apparent reason
General malaise

In these situations, you should consult a family doctor for blood tests that will tests for infections, inflammation, autoimmune disease or cancer.