8 most common causes
Why is there a lump in your armpit?
A painful lump in the armpit may feel odd but it’s usually not too worrisome. It typically means one of two things: You have a skin infection or your lymph nodes are swollen.
With all the sweat, friction, bacteria, and irritation from shaving and clothing, the armpit is a ripe environment for skin conditions like cysts or ingrown hairs.
Additionally, there are networks of lymph nodes in this area, which can swell up when your body is trying to fight off an infection. Less commonly, lumps can be caused by chronic conditions, like autoimmune diseases or cancer.
If you have a painful armpit lump, you may also have:
- Armpit rash or bumps
- Armpit itch, burning, or pain
- Oozing pus
- Painful, swollen lymph nodes in multiple parts of the body
1. Skin cyst
- Skin-colored or red bump
- Marble-size to golf ball-size armpit lump
- A central opening
- Oozing pus or white cheese-like material (keratin)
A cyst is a small sac or lump filled with fluid, air, fat, or other material. In the armpit, the most common cyst is an epidermal inclusion cyst. They can be the size of a marble or as big as a tennis ball, in worst cases. There may be a central opening on the cyst. The cyst may ooze a white cheese-like material called keratin and, when infected, pus.
Cysts are not contagious and are usually painless, but they can become infected or inflamed. When infected, they become red and tender, feel warm to the touch, and produce pus, but they rarely cause a fever.
Treatment involves cutting out the cyst. If the cyst can’t be seen or isn’t bothering you, it’s OK not to treat it. But if you don’t like how the cyst looks or it is large enough to interfere with movement, ask your doctor to remove it.
If the cyst becomes infected, your doctor will cut and drain it and prescribe an antibiotic. Steroid (kenalog) injections can help calm inflammation and reduce pain.
Patients with painful armpit lumps or bumps are often concerned about cancer. I often reassure them that most of the time these lumps are not cancers but rather infections or growths (like cysts). —Dr. Lauren Levy
2. Boil (furuncle)
- Red or pink golf ball-size bump in your armpit
- Oozing pus
A boil, or furuncle, is an infected hair follicle. Bacteria, usually Staphylococcus aureus (“staph”), can get into the hair follicle if there is open skin or irritation, which often happens after shaving.
Boils typically form in the armpit because it is a warm, moist, and dark area that bacteria can easily enter and grow. Bacteria from a razor blade can get into the skin and spread the infection.
It is important to treat the boil because the infection can spread and lead to cellulitis (skin infection). In rare cases, it can get into the bloodstream and cause a body wide infection (called sepsis).
Use warm compresses or hot-water soaks and allow the pus to drain. Your doctor may also cut and drain the boil and prescribe antibiotics. To prevent it from happening again, throw out your razors.
3. Skin abscess
- Red, fluid-filled bump ½ cm to 2 cm in diameter
- Bumps filled with pus
A skin abscess is a large pocket of pus that has formed just beneath the skin. Usually, bacteria (Staphylococcus aureus) gets in from a small cut or scratch and multiplies under the skin. The body’s white blood cells fight the invasion, killing some of the bacteria, while also forming pus inside the cavity.
The body's immune system may heal a small abscess on its own. But your doctor may need to drain or lance the abscess to clean out the pus and prescribe antibiotics. This will help relieve the pain.
If an abscess is not treated, it can grow larger and spread the bacteria through the bloodstream, which can be dangerous. Fever, body aches, and chills can be signs that the infection has spread throughout your body.
- Pink or red bumps around hair follicles
- Itch or pain
- Pus-filled bumps
Folliculitis is inflammation of the hair follicle. It occurs when bacteria (usually Staphylococcus aureus) gets into the hair follicle, causing inflammation and pus. The bacteria enters through open skin and can even live on an old razor. It can be very itchy or painful.
Often folliculitis will go away on its own. Your doctor may give you topical creams or oral antibiotics for more severe cases.
Throw away your razor blade if you have folliculitis. Changing your razor blade often can also help prevent it.
5. Ingrown hairs
- Pink or red bumps around hair follicles
- Itch or pain
- A hair in the center of the bump curled under the skin
Ingrown hairs occur when the hair itself grows back into the skin. The body sees it as a foreign object and reacts by sending inflammatory cells to the hair. This causes a red or pink bump around the hair, which can be very itchy or painful. Ingrown hairs often occur in people who have thick or coarse hair.
The treatment for ingrown hairs is to stop shaving for several days. Your doctor may prescribe a topical steroid lotion to calm inflammation or perform a quick in-office procedure to clip the hairs out of the bump, which prevents further inflammation. If you often get ingrown hairs, always shave in the direction of hair growth and use a new razor blade each time you shave.
6. Hidradenitis suppurativa
- Painful fluid-filled bumps, often the size of a golf ball
- Blackheads in the armpits
- Tunnels connecting the lumps, which may leak pus
- Additional bumps in the groin folds, under the breasts or buttocks
Hidradenitis suppurativa causes painful lumps to form under the skin. The lumps can become quite large and drain pus. When it’s chronic, it causes scarring and tunneling in the areas of the lumps and can be quite painful. The lumps can also develop in the groin folds or under the breasts or the buttocks.
No one knows the exact cause of Hidradenitis suppurativa, but it involves hair follicles that become inflamed and blocked. Genetics and hormones also play a role. Being overweight and smoking can make the condition worse. Since it is not contagious, you cannot spread it to others.
You may need topical medications, steroids injected into the bumps, or antibiotics that also act as anti-inflammatories, such as doxycycline. When the condition is severe, your doctor may prescribe oral or injectable medications that suppress your immune system. Or they may perform surgery to remove the bumps and repair the scarring/tunneling.
Most patients think hidradenitis suppurativa is an infection or a sexually transmitted disease. It is a disease of the hair follicle. There is often a genetic predisposition to this condition. Though hidradenitis suppurativa can be greatly improved by weight loss and stopping smoking. —Dr. Levy
7. Enlarged lymph nodes
- Armpit lump
- Lumps that move under the skin
Lymph nodes are the glands in your body that contain the cells of the immune system. The lymph nodes filter out bacteria and viruses. When you have a virus, such as a cold or flu, or another infection, the lymph nodes drain your system and help fight the infection. When this happens, the lymph nodes swell, which can make them painful.
Enlarged, painful lymph nodes are usually caused by a viral infection or from a local bacterial infection on the skin near the lymph nodes. You may also have a fever, chills, muscle aches, or cough and congestion with the flu or virus.
In rare cases, they may be due to an autoimmune disease. Or the cause may be a mystery.
Enlarged lymph nodes can also be a sign of cancer. But when it’s from cancer, the lymph nodes are usually not painful.
Enlarged lymph nodes caused by infections go away on their own when the infection is gone. When the cause is cancer, the enlarged bump will not go away on its own.
See your doctor about any enlarged lymph node that does not go away in several weeks.
Infectious mononucleosis, also called "mono" or "kissing disease," is a viral infection caused by Epstein-Barr virus. It is spread through saliva or other body fluids and is very contagious. Teenagers and young adults are the most likely to get it. The virus causes fever, muscle aches, fatigue, and loss of appetite. The lymph nodes in the armpits and other areas may become enlarged.
Because mononucleosis is caused by a virus, antibiotics will not help. Treatment consists of bed rest, fluids, and good nutrition. It’s important to have your doctor monitor your condition and make sure there is no secondary bacterial infection or damage to the heart, liver, or spleen.
Other possible causes
A number of conditions can also cause painful armpit lumps, though these are either rare or painful armpit lumps are not usually the main symptom. They include:
When to call the doctor
Most causes of painful armpit lumps are not immediately dangerous. But make an appointment with your primary care doctor if:
- The lump gets larger or more painful over a period of a few days.
- You have foul-smelling drainage from the armpit.
- You have other symptoms like fatigue, weight loss, night sweats, and/or swollen lymph nodes throughout the body.
- The lumps are still there after 2 weeks.
Make sure you tell your doctor if you are experiencing fevers, night sweats, or weight loss in combination with the painful armpit lump. These symptoms can be the sign of something more serious. —Dr. Levy
Should I go to the ER for painful armpit lumps?
Seek emergency treatment if you also have:
- Redness and warmth at the site of the lump
- Inability to eat or drink
- Inability to think clearly
Treatments of painful armpit lumps
- Minimize exposing the armpit to sweat. Shower immediately after working out and avoid tight clothing.
- Avoid shaving the armpit.
- Try warm compresses and/or warm baths to relieve pain.
- Take acetaminophen (Tylenol) or a nonsteroidal anti-inflammatory medication like ibuprofen (Motrin or Advil) for pain.
Other treatment options
Your doctor may offer one or more of the following:
- Prescription for oral or topical antibiotics to treat an infection.
- Prescription for oral anti-inflammatory medications.
- Referral to a dermatologist or surgeon for a biopsy of the armpit lump.
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