Swollen lymph nodes in the armpit typically appear as one or more small, rounded bumps beneath the skin that you can feel (and sometimes see) when the area is swollen enough. Normal armpit lymph nodes are usually less than 1 cm and undetectable by touch. When they swell, they can range from pea-sized to larger than 2 cm, and at that point you may notice a visible lump or fullness in the armpit area.
What They Look and Feel Like
Healthy lymph nodes in the armpit are oval or slightly lobulated, shaped like a small bean. When they swell due to infection, they keep that oval shape but become larger and more noticeable under the skin. You might see a soft bulge in the hollow of your armpit, and the overlying skin can appear slightly puffy or, in the case of infection, red and warm to the touch.
When you press on a swollen node, what you feel matters as much as what you see. Nodes that are swollen from a nearby infection tend to be tender, soft or rubbery, and they move freely when you push them with your fingertip. Nodes that feel firm, hard, or fixed in place (they don’t shift under pressure) are more concerning. A painless lump that doesn’t budge is worth getting checked promptly.
Size gives useful context. Benign lymph nodes in the armpit are typically smaller than 2 cm at their longest dimension. A node that grows beyond that, or that changes shape from oval to round, warrants closer attention. Rounding is one of the earliest visible changes associated with abnormal lymph node activity.
Where Exactly to Look
The armpit contains lymph nodes arranged in three levels, layered around the pectoralis minor muscle (the smaller chest muscle beneath the one you can flex). Level I nodes sit along the outer and lower edge of that muscle, closest to the surface and easiest to feel. Level II nodes are tucked deeper, directly behind the muscle. Level III nodes sit even deeper, near the collarbone. When people notice a swollen lump in their armpit, they’re almost always feeling a Level I node.
How to Check Your Own Armpits
The best way to examine your armpit nodes is to use the pads of your index and middle fingers, not your fingertips. Sit or stand with the arm on the side you’re checking relaxed and slightly lifted. If you’re checking your left armpit, use your right hand: reach up high into the armpit, just behind the front fold where your chest muscle meets your arm, with your fingers pointing toward your collarbone. Press gently inward and roll your fingers down along the chest wall.
You’re feeling for anything that stands out: a distinct bump, tenderness, or a firm mass. Note whether it moves freely, how large it feels, and whether one side differs from the other. Checking both armpits helps you establish what’s normal for your body.
Common Reasons They Swell
Infections or injuries of the arm, hand, or chest are the most frequent cause of swollen armpit lymph nodes. A cut on your finger, a skin infection on your forearm, or even a razor nick in the armpit itself can trigger swelling as the nodes filter bacteria from the affected area. Cat-scratch disease (from a scratch or bite by an infected cat) is a classic cause of isolated armpit swelling on one side.
Vaccines are another common and completely harmless trigger. After a COVID-19 vaccination or flu shot in the upper arm, the lymph nodes on that side often swell as the immune system responds. This swelling resolves on its own in most cases within a few weeks, though it can occasionally persist for several months. Breast imaging guidelines now recommend waiting at least 12 weeks after vaccination before following up on vaccine-related node swelling to avoid unnecessary concern.
Systemic infections like mononucleosis, HIV, and certain viral illnesses can cause lymph nodes to swell in multiple areas at once, including the armpits. In these cases, you’ll usually notice swelling in the neck or groin as well, not just one armpit.
Signs That Deserve Prompt Attention
Most swollen armpit nodes are temporary reactions to infection or immune activity. But certain features raise the likelihood of something more serious, including lymphoma or metastatic cancer from the breast or skin.
- Duration: A node that stays swollen for more than two weeks without an obvious cause like a healing wound or recent vaccination.
- Texture: A hard, firm lump that feels fixed to the surrounding tissue rather than sliding under your fingers.
- Shape: A round mass rather than an oval or bean-shaped bump. On imaging, loss of the normal fatty center of a node is one of the earliest signs of malignant involvement.
- Size: Growth beyond 2 cm, or a node that keeps getting larger over days to weeks.
- Painlessness: Counterintuitively, a painless hard lump is more concerning than a tender one. Tenderness usually signals infection.
- Accompanying symptoms: Unexplained fevers, drenching night sweats, or unintentional weight loss alongside swollen nodes can point to lymphoma or another systemic condition.
Older age and having a node that doesn’t move freely are additional risk factors that increase the likelihood a swollen node is malignant rather than reactive.
What Happens During Evaluation
If your doctor wants a closer look, the first step is usually an ultrasound. This painless imaging can reveal the internal structure of the node: whether it still has a normal fatty center, whether the outer layer (cortex) is thickened beyond 3 mm, and whether the shape has shifted from oval to round. All of these details help distinguish a reactive node from a suspicious one.
For women, a mammogram or breast tomosynthesis may be done alongside the ultrasound if there’s any concern about breast cancer. If the node looks suspicious on imaging, a needle biopsy can sample the tissue directly. Many people worry that a biopsy means cancer is likely, but biopsies are also used to confirm infections like cat-scratch disease or to rule out false alarms from imaging.
The vast majority of swollen armpit lymph nodes turn out to be benign. Knowing what a normal node looks and feels like, and what changes to watch for, puts you in a much better position to tell the difference between a routine immune response and something that needs medical attention.