A swollen lymph node in your armpit typically feels like a round, movable lump just beneath the skin, ranging from the size of a pea (about 1 cm) to a grape (about 3 cm) or occasionally larger. It may be tender to the touch, or you might notice it only because you felt something unfamiliar while showering or applying deodorant. What it feels like in terms of texture, pain, and mobility can tell you a lot about what’s causing it.
Where You’ll Feel It
Your armpit contains five groups of lymph nodes spread across the area. The ones you’re most likely to feel are the central nodes, which sit in the soft fatty tissue right in the middle of your armpit. Others are tucked along the chest wall toward the front, along the back wall near your shoulder blade, or higher up near the top of the armpit. Most people notice a swollen node by pressing into the center of the armpit with their fingertips, but depending on which group is reacting, you might feel the lump closer to your chest or toward the inner side of your upper arm.
Texture, Firmness, and Mobility
The way a swollen lymph node feels under your fingers varies depending on the cause, and those differences matter. A node that’s swollen from a common infection is usually soft or rubbery, somewhat round, and slides easily under your skin when you press on it. Think of pressing on a small grape beneath a layer of fabric. It gives a little and shifts position.
A node that feels hard, like a small stone, and doesn’t move when you push on it is a different situation. Nodes described clinically as “fixed” are ones that seem stuck to the tissue around them rather than gliding freely. Nodes can also feel “matted,” meaning several lumps seem fused together into one irregular mass. Hard, fixed, or matted nodes are less common but warrant prompt medical attention because these characteristics are more associated with serious causes, including cancer.
Pain and Tenderness
Pain is one of the most informative features. Swollen nodes caused by infection are generally tender. You might feel a dull ache in your armpit even without pressing on it, or it might only hurt when you touch the area, raise your arm, or wear a tight bra or shirt. The tenderness comes from the node expanding rapidly as your immune system ramps up, which stretches the outer capsule of the node.
A painless lump is worth paying closer attention to. Infectious swelling tends to present as a tender, soft, mobile mass, while malignant swelling more often presents as a nontender, hard, fixed mass. That doesn’t mean every painless lump is dangerous. Some reactive nodes simply aren’t very tender. But a painless node that’s also firm and doesn’t move freely is the combination that doctors take most seriously.
Common Reasons for the Swelling
The armpit nodes filter lymph fluid from your arm, chest wall, and upper back, so they react to a wide range of triggers. The most common causes are benign:
- Skin irritation or minor injury: Shaving nicks, ingrown hairs, or a new deodorant can trigger a local immune response. These nodes are usually small, mildly tender, and resolve within a week or two.
- Skin infections: A cut on your hand, a bug bite on your arm, or a deeper infection like cellulitis can cause one or more armpit nodes to swell noticeably. The node often becomes tender and may reach 2 cm or more.
- Cat scratch fever: A bacterial infection from a cat scratch or bite can cause significant lymph node swelling near the site of the wound, and the armpit is a common location for scratches on the hand or arm.
- Vaccination: COVID-19 vaccines and other injections given in the upper arm commonly cause armpit swelling on the same side. Onset is typically within one to two weeks after the shot. Most vaccine-related swelling improves within 30 to 45 days, though some cases take longer. One case study documented a node taking roughly six months to fully return to normal size.
- Upper respiratory infections: A cold, flu, or other viral illness can cause generalized lymph node swelling, including in the armpits.
What Size Is Worth Noting
Normal lymph nodes in the armpit are usually under 1 cm (smaller than a pea) and you can’t feel them at all. Once a node grows large enough to detect with your fingers, it’s technically enlarged. A pea-sized lump (about 1 cm) from a recent cold or minor skin irritation is common and usually resolves on its own. A node the size of a grape (about 3 cm) or larger deserves medical evaluation, especially if it’s been present for more than two weeks and you can’t link it to an obvious cause like a recent infection or vaccine.
Nodes that keep growing over weeks, rather than shrinking, are more concerning than nodes that stay the same size or get smaller. If you notice a lump, it’s useful to check it every few days and note whether it’s changing.
What Doctors Look For
If you get your armpit node evaluated, the doctor will likely start by feeling it and asking about recent infections, injuries, or vaccinations. If imaging is needed, ultrasound is the standard tool. On ultrasound, a healthy lymph node has an oval shape with a bright fatty center (called the hilum). When a node is reacting to infection, the outer layer (cortex) may thicken, but that bright center stays visible.
The features that raise concern on ultrasound include a round rather than oval shape, cortical thickening beyond 3 mm, and loss of that fatty center. A node where the center is completely replaced by abnormal tissue has the highest association with malignancy, with a predictive value between 58% and 97% depending on the study. Cortical thickening alone, on the other hand, is considered the earliest change but is nonspecific, meaning it can show up in both harmless and serious conditions. If the ultrasound looks suspicious, a biopsy (removing a small tissue sample with a needle) is the next step.
Signs That Need Prompt Attention
Most swollen armpit nodes are your immune system doing its job and will shrink on their own. But certain combinations of features point to something that needs evaluation sooner rather than later. A node that is hard, fixed in place, painless, and growing over weeks checks the most concerning boxes. Accompanying symptoms like unexplained weight loss, drenching night sweats, or persistent fevers without an obvious infection (sometimes called “B symptoms” in the context of lymphoma) add urgency. Skin changes over the lump, such as redness, dimpling, or warmth, can indicate either infection or inflammatory breast cancer and also warrant a visit.
A single soft, tender, marble-sized lump that appears after you nicked yourself shaving or got a flu shot is, by contrast, exactly what a normal immune response looks like. If it shrinks over a couple of weeks, you can generally stop worrying about it.