What Causes an Armpit Lump & How to Address Your Symptoms
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An armpit lump, or axillary lump, is often caused by swollen lymph nodes in the armpit. This condition can also be associated with tenderness or pain in the lump under the arm. A small or pea-sized lump in the armpit can also be caused by a skin infection, like a cyst, or ingrown hair. Read below for more causes and treatments options.
Hallmarks of armpit lumps
Lumps in the armpit can have a wide range of causes, and most are not serious and can be easily treated. However, a new, unexplained lump under your arm should be examined by your medical provider, especially if you are a woman.
Most of the time, these armpit lumps are swollen lymph glands. The lymphatic system, made up of many small glands and a circulatory system of its own, runs throughout the body and is responsible for filtering out any infectious agents. That's why lymph glands, or nodes, are very important but also vulnerable to infections and tumors.
Common characteristics of an armpit lump
- Large or very small
- Soft, rubbery, or firm
- Painful, tender, or painless
- Reddened, or with normal skin color
- Hot to the touch, or normal
- Barely visible under the skin or an obvious lump that hangs down
Common accompanying symptoms
Fever is sometimes present if you have a painful armpit lump.
Duration of symptoms
If the armpit lump is actually swollen lymph nodes due to an infection, the swelling usually goes away soon after the infection is cleared up.
Who is most often affected?
People who are most likely to experience armpit lumps include the following.
- Women: Lumps may be caused by underarm shaving, breastfeeding, or breast cancer.
- Anyone with an infection: Such as a systemic illness or a localized infection in the arm or breast
- Anyone with the Epstein-Barr virus (EBV): This may contribute to some forms of lymphatic cancer.
Are armpit lumps serious?
The severity of your armpit lump is ultimately determined by the cause.
- Not serious: A small lump or swelling that clears up on its own is probably not serious.
- Moderately serious: A lump that is reddened, painful, and/or persistent should be examined by a medical provider.
- Serious: A lump that is large, reddened, painful, and continues to grow, especially if you also have a fever, should be examined by a medical provider.
What causes a lump under your armpit?
Many conditions can have an armpit lump as a symptom. The most common are those involving the lymph nodes under the arm, as well as infections and, more rarely, tumors.
Most common causes
The most common causes of armpit lumps include the following.
- Enlarged lymph nodes: These can feel like lumps under the skin of the armpit and are a sign the body is fighting a systemic disease such as a bacterial or a viral illness.
- Bacterial infections: These can cause painful, reddened swellings called abscesses or boils. Bacteria that commonly affect the lungs and other areas include staphylococcus or streptococcus, as well as Mycobacterium and Bartonella.
- Viral infections: These can also cause upper respiratory and ear infections, as well as many other illnesses.
- Fungal infections: Candida, commonly called "yeast," can cause clusters of small swellings under the arm.
- Single-celled parasitic organisms: Toxoplasma gondii can cause flu-like symptoms and lymph node swelling.
- Autoimmune illnesses: These cause inflammation throughout the body that provokes swelling in the lymph nodes.
- Inflammation of sweat glands under the arm: This can cause painful, reddened clusters of large and small bumps in and under the skin, and may also be related to infected hair follicles, infected ingrown hairs, or infected insect bites.
Contact allergies can cause armpit swelling as one or more lumps.
- Antiperspirants and deodorants
- Laundry soaps and fabric softeners
Less common causes
The following are less common causes of armpit lumps.
- Abscesses or boils: A lump of bacterial infection, called an abscess or boil, can form just under the skin of your armpit, arm, or breast. It is often caused by shaving. Even a small break in your skin can allow bacteria, most often Staphylococcus or Streptococcus, to get in and begin to grow.
- Cysts: A cyst is a small, isolated sac of fluid, pus, air, or other substance that can form almost anywhere in the body. Cysts are usually the result of some trauma or irritation such as shaving, having ingrown hair, and/or using an antiperspirant (antiperspirants block the pores).
- Insect bites: An insect bite, especially a mosquito bite, can form a red bump under your arm. These bites are usually very itchy.
Certain medications can cause a kind of allergic reaction that includes swollen lymph nodes under the arm. Vaccines work by actually giving you a very mild form of the disease they are protecting against. This mild disease can be enough to cause temporary swelling of the lymph nodes under your arm.
Causes of armpit lumps that are rarer include the following.
- Vaccines: Some vaccinations can cause swollen lymph nodes in your armpit and elsewhere because of the way the vaccine stimulates your immune system.
- Blocked milk duct: In women who are nursing, a milk duct can sometimes become blocked. This can cause lumps to form throughout the breast and armpit.
- Lipoma: This is a benign fatty tumor often found under the arm.
- Lymphoma: This is cancer of the lymph nodes.
- Breast cancer: An armpit lump can be a sign of breast cancer in anyone, not just women.
This list does not constitute medical advice and may not accurately represent what you have.
A cyst is a small sac or lump, filled with fluid, air, fat, or other material, that begins to grow somewhere in the body for no apparent reason. A skin cyst is one that forms just beneath the skin.
It's believed that skin cysts form around trapped keratin cells – the cells that form the relatively tough outer layer of the skin.
These cysts are not contagious.
Anyone can get a skin cyst, but they are most common in those who are over age 18, have acne, or have injured the skin.
Symptoms include the appearance of a small, rounded lump under the skin. Cysts are normally painless unless infected, when they will be reddened and sore and contain pus.
Diagnosis is made through physical examination. A small cyst can be left alone, though if it is unsightly or large enough to interfere with movement it can be removed in a simple procedure done in a doctor's office. An infected cyst must be treated so that the infection does not spread.
Top Symptoms: skin-colored armpit bump, marble sized armpit lump, small armpit lump
Symptoms that always occur with skin cyst: skin-colored armpit bump
Urgency: Wait and watch
A skin abscess is a large pocket of pus that has formed just beneath the skin. It is caused by bacteria getting under the skin, usually through a small cut or scratch, and beginning to multiply. The body fights the invasion with white blood cells, which kill some of the infected tissue but form pus within the cavity that remains.
Symptoms include a large, red, swollen, painful lump of pus anywhere on the body beneath the skin. There may be fever, chills, and body aches from the infection.
If not treated, there is the risk of an abscess enlarging, spreading, and causing serious illness.
Diagnosis is made through physical examination.
A small abscess may heal on its own, through the body's immune system. But some will need to be drained or lanced in a medical provider's office so that the pus can be cleaned out. Antibiotics are usually prescribed.
Keeping the skin clean, and using only clean clothes and towels, will help to make sure that the abscess does not recur.
Top Symptoms: rash with bumps or blisters, red rash, red skin bump larger than 1/2 cm in diameter, pus-filled rash, rash
Symptoms that always occur with skin abscess: rash with bumps or blisters
Urgency: Primary care doctor
Lipoma is a word that translates as "fatty tumor," but a lipoma is not cancer. It is simply a growth of fat between the muscle layer and the skin above it.
The exact cause is not known. The condition does run in families and is associated with other unusual syndromes such as adiposis dolorosa, which is similar. Lipomas most often appear after age 40.
Symptoms include a soft, easily moveable lump beneath the skin, about two inches across. A lipoma is painless unless its growth is irritating the nerves around it. They are most often found on the back, neck, and abdomen, and sometimes the arms and upper legs.
It is a good idea to have any new or unusual growth checked by a medical provider, just to make certain it is benign.
Diagnosis is made through physical examination, biopsy, and imaging such as ultrasound or CT scan.
Most of the time, treatment is not necessary unless the lipoma is unsightly or is interfering with other structures. It can be removed through surgery or liposuction.
Top Symptoms: skin-colored groin bump, marble sized groin lump, small groin lump
Symptoms that always occur with lipoma: skin-colored groin bump
Urgency: Wait and watch
A furuncle, also called a boil, is infection of a hair follicle. The infection forms under the skin at the root of the hair and may occur anywhere on the body.
The infection is caused by bacteria, most often Staphylococcus aureus or "staph." Irritation caused by clothes or anything else rubbing the skin can cause the skin to break down and allow bacteria to enter.
Staph bacteria are found everywhere. Frequent and thorough handwashing, and otherwise maintaining cleanliness, will help to prevent its spread.
Most susceptible are those with a weakened immune system; diabetes; and other skin infections.
Symptoms include a single bump under the skin that is swollen, painful, and red, and contains pus.
It is important to treat the boil, since infection can spread into the bloodstream and travel throughout the body.
Diagnosis is made through physical examination and sometimes fluid sample from the boil.
Treatment may involve incision and drainage of the infection, followed by creams to apply to the site of the boil and/or a course of antibiotic medicine.
Top Symptoms: pink or red facial bump, small facial lump, painful facial bump, marble sized facial lump, constant skin changes
Symptoms that always occur with boil (furuncle): pink or red facial bump
Symptoms that never occur with boil (furuncle): fever
Enlarged lymph nodes in the armpit
Enlarged lymph nodes occur when the node becomes larger as it fills with inflammatory cells. This often is a result of an infection but can occur without a known cause.
Top Symptoms: armpit lump, movable armpit lump
Symptoms that always occur with enlarged lymph nodes in the armpit: armpit lump
Symptoms that never occur with enlarged lymph nodes in the armpit: fever, unintentional weight loss, hard lump in the armpit
Urgency: Phone call or in-person visit
Pimples are also called comedones, spots, blemishes, or "zits." Medically, they are small skin eruptions filled with oil, dead skin cells, and bacteria.
Pimples often first start appearing at puberty, when hormones increase the production of oil in the skin and sometimes clog the pores.
Most susceptible are teenagers from about ages 13 to 17.
Symptoms include blocked pores that may appear flat and black on the surface, because the oil darkens when exposed to the air; blocked pores that appear white on the surface because they have closed over with dead skin cells; or swollen, yellow-white, pus-filled blisters surrounded by reddened skin.
Outbreaks of pimples on the skin can interfere with quality of life, making the person self-conscious about their appearance and causing pain and discomfort in the skin. A medical provider can help to manage the condition, sometimes through referral to a dermatologist.
Diagnosis is made through physical examination.
Treatment involves improving diet; keeping the skin, hair, washcloths, and towels very clean; and using over-the-counter acne remedies.
Top Symptoms: pink or red facial bump, small facial lump, painful facial bump, marble sized facial lump
Symptoms that always occur with pimple: pink or red facial bump
Folliculitis is a common skin problem where hair follicles are infected by bacteria or fungi.
Top Symptoms: small facial lump, pink or red facial bump, face itch, facial bump leaking yellow/milky fluid, yellow or white facial bump
Symptoms that always occur with folliculitis: small facial lump
Hodgkin lymphoma, formerly known as Hodgkin's lymphoma or Hodgkin's disease, is cancer of the lymphatic system. It is believed to be caused by a mutation in one of the body's immune system cells, called a B cell.
Most susceptible are those under age 30 or over age 55, with a family history of the disease, as well as anyone with a history of any illness caused by the Epstein-Barr virus.
Symptoms include swelling of lymph nodes in groin, armpits, and neck; lowered tolerance to drinking alcohol, including pain in lymph nodes afterwards; unintended weight loss; fever; chills; night sweats; and itching.
There are good treatments available for Hodgkin lymphoma, so it is important to see a medical provider about these symptoms as soon as possible.
Diagnosis is made through physical examination; blood tests; imaging such as x-ray, CT scan, or PET scan; and sometimes lymph node biopsy and/or bone marrow sample.
Treatment involves a combination of chemotherapy and radiation therapy. Bone marrow transplant, also called stem cell transplant, can be done in some cases.
Top Symptoms: fatigue, loss of appetite, abdominal pain (stomach ache), shortness of breath, fever
Symptoms that never occur with hodgkin's lymphoma: pulsing armpit mass, armpit lump that comes and goes, shrinking armpit lump, pink or red armpit bump, black or brown armpit bump, yellow or white armpit bump, bleeding armpit bump
Urgency: Primary care doctor
Warts, also called common warts or verrucae, are small, rough, rounded growths on the top layer of the skin. They may appear alone or in clusters. Common warts are caused by the human papillomavirus (HPV) and are contagious through direct contact. They may spread from one place on the body to another simply through touch.
There are several types of breast cancer, depending on the part of the breast where it starts. The most common types are ductal carcinoma in situ (DCIS), invasive ductal carcinoma and invasive lobular carcinoma.
Women over age 50 with a family history of the disease, and/or certain genetic factors, are most at risk, but anyone can get breast cancer at any age. It is rare in men but does occur.
Symptoms include a lump, thickening, or pain anywhere in the breast or armpit; red, flaky, or irritated breast or nipple skin; nipple discharge; and any area of irregular skin or misshapenness.
Many harmless conditions can cause similar signs, so it is important to see a medical provider about any of these symptoms.
Diagnosis is made through physical examination; imaging such as ultrasound, mammogram, or MRI; and sometimes biopsy.
Treatment involves a combination of surgery, radiation therapy, and chemotherapy.
The best prevention is a combination of screening mammograms as recommended by the medical provider, and monthly self-examination.
Top Symptoms: breast pain, armpit lump, breast mass or retraction, breast lump, nipple discharge
Urgency: Primary care doctor
Treatments for bumps under the armpit
Armpit lump remedies that you can try at home include the following.
- Drink plenty of fluids: Especially if you have a fever
- Pain medication: Take over-the-counter non-steroidal anti-inflammatory drugs like ibuprofen (Advil, Motrin).
- Hygiene: Keep the underarm area very clean and dry and be gentle while shaving. This will help to avoid infections and ingrown hairs.
When to see a doctor
You should see a doctor for the following.
- Any unexplained lump in your armpit: Especially if you are a woman and have no other symptoms of illness
- Swelling that persists or worsens over several days: Especially if you also develop a fever or other symptoms of illness.
- Examinations: You should point out any unexplained armpit lumps, especially ones that have persisted for more than a week or so.
- Treatments: These should be given for any lumps that appear to be infected or for any systemic illness that appeared around the same time as the lump.
When it is an emergency
Seek immediate treatment in the emergency room if you have a lump in your armpit that is reddened and painful, and you also have a fever and/or difficulty breathing or swallowing.
- You have started a new medication: Seek care if a widespread skin rash, fever, and swollen lymph nodes occur.
- You have an abscess and additional symptoms: Such as high fever, chills, shaking, sweating, and rapid breathing and heart rate.
FAQs about armpit lumps
Why is the lump on my armpit painful?
Lumps in the armpit, even painful lumps, are common. The majority of armpit lumps are not life- or limb-threatening. Usually, a painful lump in the armpit is due to a clogged pore, a swollen lymph node, or a cyst. These bumps may be pea-sized, inflamed, tender to the touch, and can cause pain when lifting the arm as well.
Will my armpit lump go away on its own?
Yes, most armpit lumps will dissipate with time, depending on the cause. Lumps from infection or blocked pores will disappear as the infection or bodily illness resolves. In the case of a skin infection, this may take a week or so. In the case of a swollen lymph node from a viral infection, it may take up to 10 days. If the lump is from using a deodorant or lotion that blocks pores (e.g. one containing aluminum), resolution may require switching products. Persistent armpit lumps, especially if they are hard and fixed in place, deserve medical attention.
Why do I get lumps only under one arm?
Lumps under one arm are often due to blocked pores. This can be due to overuse of one arm, causing more sweating and a backup of sweat and bacteria. it can be due to the application of deodorant or lotion more heavily on one arm than the other. It can be due to an infection in the upper arm or forearm of the corresponding armpit as the lymph nodes respond to increased white blood cells, or it can rarely be due to a local malignancy or cancer. If it does not resolve, you may require medical evaluation.
Can shaving cause armpit lumps?
Yes, shaving can cause armpit lumps. This is most commonly caused by ingrown hairs or small cuts and abrasions in the skin of the armpit. As they heal and skin regrows, the hair may grow into the skin instead of outward. Hair follicles are often colonized by bacteria. If the hair grows into the skin, the bacteria will have no means of drainage from the skin and a bacterial infection may form, causing inflammation and pain.
Can I pop the lump on my armpit?
Yes. If it is a superficial and small local infection or pimple it can be popped. However, it is best not to pop any pustules or larger pimples in the armpit without medical evaluation to rule out other conditions. The lump, if popped, may spread the bacteria, causing more pimples or further inflammation.
Are cancerous armpit lumps painful?
A lump that is caused by cancer may or may not be painful. Pain is not an indication of whether or not any particular lump is concerning. Most often, a cancerous lump will be hard and painless; but again, this is not always the case. Any suspicious lumps should be examined by your physician.
Are cancerous armpit lumps hard and immovable?
In most cases, yes, and in most cases, it will be painless. A benign lump is most often soft and moveable since it only contains fluid and fat, but harmless scar tissue can form lumps, too, and those will seem hard. The only way to know for certain is to have your physician examine any suspicious lumps.
What causes a soft armpit lump?
A lipoma is a small lump or bulge that is primarily made up of fat. This makes it soft, rubbery, and easily moveable. These are rarely cancerous and usually not painful. Another common soft lump is a cyst, a small sac filled with fluid, pus, or even gas. These are also soft and moveable, rarely painful, and almost never cancerous.
What causes a sore or painful armpit lump?
A hair follicle, sweat gland, or small cut in the armpit can become infected and form an abscess, which is a reddened, painful lump. Some women have breast tissue that extends up into the armpit and, as with the rest of the breast, this tissue can also become somewhat tender and lumpy just before menstruation.
Does breastfeeding cause lumps to form in the armpit?
Some women have breast tissue that reaches into the armpit, and this tissue will also become engorged and somewhat lumpy during breastfeeding. Mastitis, which is an infection of breast tissue in a nursing mother, can cause the lymph nodes in the armpit to swell in the same way any other illness does.
Questions your doctor may ask about armpit lump
- What color is the bump?
- Any fever today or during the last week?
- Do you have a rash?
- Do you feel pain when you touch the bump?
Self-diagnose with our free Buoy Assistant if you answer yes on any of these questions.
Janeen has worked over eight years as a full-time medical transcriptionist, specializing in pain management and gynecologic oncology. She later began transcribing reports for hospital emergency rooms and acute care admissions. This background gave her a strong medical vocabulary as well as a heart for making medical information accessible to the average person, leading her to work as a medical writer. She began as a pre-veterinary medicine major at Texas State University.
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