Finding a lump in your armpit can be concerning.
But it doesn’t always mean a serious health issue—there are common causes of lumps in armpits, such as swollen lymph nodes.
But there may also be serious health concerns, especially if a lump appears and never goes away, or gets bigger over time.
In this article, I’ll talk about some of the possible causes of a lump in your armpit, how to get the right diagnosis, and types of treatment available for lumps in armpits.
Lump in Armpit Possible Causes
A lump in the armpit is a swollen bump or enlargement under the arm.
The most common causes of these are swollen lymph nodes, cysts, or infections.
An armpit lump may also be called lymphadenopathy, axillary lymph enlargement, or axillary abscess, depending on what is causing it.
Most common causes
- Infections: Your lymph nodes are small organs that act like filters in the body: They trap foreign objects like viruses and bacteria, and help the body get rid of them. So when you have a bacterial or viral infection, your lymph nodes can swell, causing a small lump. There are lymph nodes throughout the body, but the nodes in the neck and armpits may be more noticeable when they swell. Typically, swollen lymph nodes from infections will feel tender to the touch. They may also accompany other signs of infection, like fever.
- Cysts: Cysts are fluid-filled sacs that can form in many places throughout the body, including the armpit. They may be large or small. Cysts may come and go, or they may persist.
- Lipomas: Lipomas are lumps that form from fatty tissue. They are benign (not cancerous) soft-tissue tumors that tend to appear after age 40. Lipomas are typically slow-growing and do not always require medical treatment once a diagnosis has been made. Sometimes lipomas occur as a sign of other diseases or disorders.
- Fibroadenomas: Fibroadenomas are solid, noncancerous lumps. They are found in the breasts of people born female, typically between ages 15-35. If they are at the side of the breast, they may seem to be in the armpit. They can feel hard, like a marble, and vary in size.
- Autoimmune disorders: Certain autoimmune disorders can influence how the lymphatic system works, which may lead to more frequently swollen lymph nodes. These can include lupus or rheumatoid arthritis. If you have a known autoimmune disorder but notice a new lump in your armpit, tell your doctor. Some people may also be born with disorders that can increase the odds of developing swollen lymph nodes, such as autoimmune lymphoproliferative syndrome (ALPS).
- Vaccines: Some vaccines, including some COVID-19 vaccines, can lead to short-term swollen lymph nodes in the armpits. While it does not happen to everyone, the lumps gradually decrease and resolve on their own. It is a sign of the immune system working in response to the vaccine.
- Hidradenitis suppurativa: Hidradenitis suppurativa is a condition in which hair follicles become blocked and cause small, painful lumps to form under the skin. It is thought to be genetic or caused by hormones, tobacco use, or excess weight. It can be a harmless condition, but can also result in infections or other complications which require ongoing medical care.
- Allergic reactions to body care products: In some cases, allergic reactions to antiperspirants, deodorants, lotions, soaps, or shaving products may lead to swelling or lumps under the armpit. These may also include redness of the skin, itching, or burning. Discontinue use of products that you suspect are causing allergic reactions. See your healthcare provider if the symptoms worsen or do not go away on their own.
More serious causes
While most armpit lumps come from common causes, sometimes they may indicate a serious underlying health issue.
Lumps that appear and never go away, or gradually get larger, can be signs of concern.
Even if you think the cause is common, tell your doctor about any lumps in your armpit that you notice.
A medical exam and further testing can determine the cause.
Some potentially serious causes of armpit lumps could include:
- Breast cancer: Armpit lumps that occur from breast cancer may feel hard, may not be painful, and can vary in size. The side of the breast can sometimes be mistaken for the armpit, so a lump felt anywhere under the arm should be examined by a medical provider.
- Lymphoma: There are many different types of lymphoma, a type of cancer that results when certain cells of the immune system reproduce incorrectly. Because immature or excessive types of immune cells may accumulate in the lymphatic system, lumps may be found in the lymph nodes of the armpits or elsewhere. Simple blood tests can be a starting point to rule out lymphoma, and additional testing like a biopsy can confirm or rule out the diagnosis.
- Leukemia: Leukemia is a type of cancer that occurs when your bone marrow produces large numbers of abnormal cells. Lumps or swollen lymph nodes that appear and do not go away, or come on without an accompanying viral or bacterial illness, should be reported to a medical provider. Blood tests that examine the numbers and types of red and white blood cells, as well as metabolic function, can identify abnormal processes that may be indicative of leukemia.
Armpit Lump Diagnosis
Your medical provider is the only one who can determine the cause of your armpit lump.
Sometimes a single physical examination can provide an answer.
Other times, follow-up testing may be required. Your medical provider may also suggest watching for changes over time.
A physical examination to assess an armpit lump will include gently feeling the area with a hand.
This will help your doctor determine the size, consistency, texture, and density of the lump.
The medical provider may also examine other areas of the body or other lymph nodes.
Testing that your medical provider may use to find a correct diagnosis for a lump in the armpit may include:
- A complete blood count
- A metabolic panel
- A chest X-ray
- CT scan
- Other testing based on any other symptoms that are present
Your doctor will also ask you questions about your medical history, recent symptoms or changes to how you feel.
Differences in men and women
Women should be extra aware of armpit lumps, as they may be an indicator of breast cancer.
While breast cancer can affect males as well (men account for approximately 1% of all breast cancers), it is far more common in women.
Women should do monthly breast self-exams.
They should also see medical providers regularly for routine screenings and care.
Any new lumps, in the armpit or elsewhere, should be reported to a healthcare provider right away.
People who were born male should still report lumps to their doctor or healthcare provider, but the likelihood of those lumps being related to breast cancer are significantly lower.
Regular breast exams are important for women for the following reasons:
- Breasts can change throughout the menstrual cycle in response to hormones. At certain times of the cycle, especially before and during a period, breasts may feel tender, sensitive, or even feel more lumpy from water retention.
- The best practice is to perform self-exams at the same time every month, usually 1-3 days after a period has ended. This is the time in a cycle where there is the least amount of hormonal changes to the breasts.
- Routine breast cancer screenings are important for everyone, but even more so if there is any family history of breast cancer, or if your doctor has indicated that there are other risk factors. Screening guidelines can vary, but generally women should start getting regular mammogram screenings at age 40.
Treating Armpit Lumps
Most common causes of armpit lumps do not require treatment.
If a benign lump, like a lipoma, is bothersome, doctors can suggest treatment options or removal.
Swollen lymph nodes that are caused by infections or non-serious illness typically resolve on their own once the infection subsides.
Your doctor may ask that you monitor the lump for changes in size or other symptoms.
In some cases, your doctor may recommend at-home care for lumps that are caused by infections or swollen lymph nodes.
These could include:
- Warm compresses
- Heating pads
- Creams or ointments for allergic reactions
- Over-the-counter pain relievers
- Antibiotics, if it is caused by a bacterial infection
If the armpit lump is concerning for cancer, your medical provider will refer you to an oncologist for further evaluation and treatment.
Further evaluation may include imaging or a biopsy, and treatment depends on the type of cancer and the stage it is diagnosed in.
Common treatment for cancers that may cause armpit lumps include:
- Surgical removal
When to See a Medical Provider
If you notice any type of lump in your armpit, check in with your doctor to find out whether a physical examination is needed.
It’s concerning to notice a lump in your armpit.
But you should not delay medical care because you are worried.
Most lumps in armpits are not serious causes for concern, and your medical provider can put your mind at ease.
If you do require further testing, or your doctor does diagnose a more serious cause, the earlier you are diagnosed, the better your chances of receiving effective care and recovering.
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K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.
K Health has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations. We avoid using tertiary references.
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Lipoma - arm. (2021).
Systemic lupus erythematosus (SLE) lymphadenopathy presenting with histopathologic features of Castleman' disease: a clinicopathologic study of five cases. (1997).
Rheumatoid arthritis. (2020).
Autoimmune lymphoproliferative syndrome. (2018).
Lymphadenopathy Associated With the COVID-19 Vaccine. (2021).
Hidradenitis Suppurativa. (2022).
Breast cancer. (2018).