Swollen Lump in Your Armpit: Causes and Cure

TL;DR

• Most armpit lumps are swollen lymph nodes caused by infections, irritation, or vaccine reactions and resolve on their own within 1 to 3 weeks.
• A lump that is painless, rock-hard, fixed in place, larger than 2 cm, or growing steadily should be evaluated by a doctor promptly.
• Accompanying symptoms like unexplained weight loss, night sweats, or persistent fever can indicate lymphoma or metastatic cancer and need immediate medical attention.

What Causes a Swollen Lump in Armpit?

Your armpit contains lymph nodes, hair follicles, sweat glands, fatty tissue, and blood vessels. Any of these structures can produce a palpable lump. The most common causes range from completely benign to, in rarer cases, serious.

Swollen lymph nodes from infection are by far most frequent cause. When your body fights off a cold, flu, sore throat, ear infection, skin wound on hand or arm, or even a dental infection, lymph nodes nearest infection site enlarge. The armpit nodes drain fluid from arms, chest wall, and upper back, so infections in any of those areas can trigger underarm swelling. These nodes typically feel soft, moveable, and tender. They usually shrink back to normal within one to three weeks once infection clears.

Vaccine reactions are another very common trigger. The COVID-19 vaccines, flu shots, and other immunizations can cause lymph node swelling in armpit on side of injection. This is a normal immune response and usually resolves within a few weeks. If you have recently been vaccinated and notice a lump, this is most likely explanation.

Skin-related causes include folliculitis (inflamed hair follicles from shaving or friction), ingrown hairs, sebaceous cysts (blocked oil glands that form round, moveable lumps under skin), and boils or abscesses. These tend to be painful, red, warm to touch, and located more superficially in skin rather than deep under it.

Allergic reactions to deodorants, antiperspirants, soaps, or laundry detergents can cause localized inflammation and swelling in armpit. Switching products and seeing if lump resolves is a reasonable first step if you suspect this.

Hidradenitis suppurativa is a chronic skin condition where sweat glands and hair follicles in armpit (and groin) become repeatedly blocked and inflamed. It causes deep, painful lumps that may drain pus, heal with scarring, and recur. It affects about 1% of population and is three times more common in women. If you get painful lumps in your armpits repeatedly, this condition is worth discussing with a dermatologist.

Lipomas are soft, rubbery collections of fat cells that form under skin. They are completely benign, painless, and moveable. They grow very slowly and are not dangerous, though they can be surgically removed if they become bothersome.

For a closer look at what lumps in other locations might mean, this guide covers a related topic: Lump on Back

When Should You Be Concerned?

While most armpit lumps are harmless, certain characteristics should prompt you to see a doctor sooner rather than later.

A painless lump is actually more concerning than a painful one. Infections and inflammation tend to cause pain and tenderness. Cancerous lymph nodes are more often painless. This is counterintuitive, but a lump that does not hurt and has no obvious cause deserves closer attention.

A hard, fixed lump that does not move when you press on it is another warning sign. Normal lymph nodes and benign lumps like lipomas or cysts tend to be soft or rubbery and shift under your fingers. A rock-hard mass that feels anchored to tissue around it may need imaging and possibly a biopsy.

A lump that grows steadily over weeks should be evaluated. Reactive lymph nodes from infection typically reach their peak size within a few days and then start shrinking. A lump that keeps getting bigger, especially if it exceeds 2 centimeters (roughly size of a large grape), warrants investigation.

A lump that persists for more than two to three weeks without an obvious explanation like an active infection or recent vaccination should be checked by your provider.

The National Cancer Institute notes that enlarged lymph nodes can be an early sign of lymphoma (cancer of lymphatic system) or metastatic disease, where cancer from another site (most commonly breast cancer) has spread to lymph nodes. However, it is important to emphasize that this is a rare cause relative to much more common benign explanations.

NCI Lymphoma Information

What Are Red Flag Symptoms?

Beyond lump itself, certain accompanying symptoms can indicate a more serious underlying condition. These are sometimes called "B symptoms" in context of lymphoma, but they can also appear with other systemic illnesses.

Unexplained weight loss of more than 10 pounds over a period of weeks to months, without dieting or increased exercise, is a significant warning sign that should always be evaluated.

Drenching night sweats that soak through your clothes or sheets are different from normal nighttime warmth. This type of sweating, especially when combined with an unexplained lump, warrants medical attention.

Persistent fever above 100.4 degrees Fahrenheit (38 degrees Celsius) that lasts more than a few days without an obvious source like a cold or flu should be reported to your provider.

Extreme fatigue that is out of proportion to your activity level and does not improve with rest can sometimes accompany lymphoma or other systemic conditions.

If you have a swollen lump in your armpit along with any of these symptoms, do not wait to see if it resolves on its own. See your provider promptly.

How Are Armpit Lumps Diagnosed?

Your provider will start with a physical examination. They will assess lump's size, shape, texture, mobility, and tenderness. They will also check for lumps in other lymph node regions (neck, groin, above collarbone) and examine your breasts if relevant.

Depending on what physical exam suggests, further testing may include blood work (a complete blood count can reveal signs of infection or blood cancers), imaging (an ultrasound is usually first-line imaging test for an armpit lump, though a CT scan may be ordered if lymphoma or metastatic disease is suspected), and a biopsy (either a fine-needle aspiration or a core needle biopsy, where a small sample of tissue is removed and sent to a lab for analysis).

In many cases, physical exam and a brief period of watchful waiting are all that is needed. If lump is soft, moveable, tender, and you have an obvious explanation like a recent cold or vaccine, your provider may simply ask you to monitor it and return if it does not resolve within two to three weeks.

What Can You Do at Home?

For lumps that are clearly related to infection or inflammation, a few simple measures can help.

Warm compresses applied to area for 15 to 20 minutes, three to four times a day, can help reduce swelling and encourage drainage of superficial infections. Over-the-counter pain relievers like ibuprofen or acetaminophen can manage discomfort. Keep area clean and dry, especially if you shave your underarms. Avoid irritating products if you suspect an allergic reaction.

Do not try to squeeze, pop, or drain an armpit lump yourself. This can introduce bacteria, worsen infection, or cause scarring.

If you have noticed swollen nodes in other areas as well, such as under your chin or jaw, this resource covers what that might mean: Lymph Nodes Under Chin

Conclusion

A swollen lump in armpit is common and is usually caused by a swollen lymph node responding to an infection, a vaccine, or local skin irritation. Most lumps are soft, tender, moveable, and resolve on their own within a few weeks. A lump that is painless, hard, fixed, growing, larger than 2 cm, or accompanied by unexplained weight loss, night sweats, or persistent fever needs prompt evaluation to rule out lymphoma, breast cancer, or other serious conditions. When in doubt, have your provider take a look. The peace of mind from a simple exam is always worth it.