Bumps under your armpits are usually caused by irritated hair follicles, swollen lymph nodes, or clogged pores. The armpit is a warm, moist area packed with hair follicles, sweat glands, and lymph nodes, making it one of the most common places on the body to develop lumps or bumps. Most causes are harmless, but the size, texture, and behavior of the bump can tell you a lot about what’s going on.
Ingrown Hairs and Folliculitis
Shaving is the single most common trigger for armpit bumps. When a hair curls back into the skin instead of growing outward, it creates a small, red, sometimes painful bump called an ingrown hair. If bacteria get into the irritated follicle, you develop folliculitis, which looks like a cluster of small red or white-headed bumps that may itch or sting.
Folliculitis often clears up on its own within a week or two with basic care. Gently washing the area twice a day with an antibacterial cleanser (benzoyl peroxide works well) and using a clean towel each time can speed things along. A nonprescription hydrocortisone cream helps with itching. If the bumps keep coming back or spread, a doctor can prescribe an antibiotic lotion or, in stubborn cases, oral antibiotics. For people who get repeated ingrown hairs, laser hair removal is sometimes recommended as a longer-term fix.
Boils and Cysts
A boil starts as a tender, swollen lump that grows over several days and fills with pus. It’s essentially a deep infection in a single hair follicle. When several boils merge together, the result is a larger, more painful mass called a carbuncle. Both tend to come to a head and drain on their own, but a large one may need to be lanced by a doctor to relieve pressure and reduce scarring.
Cysts are different. An epidermal cyst feels firm, sits just under the skin’s surface, and is often tender to the touch. You may notice redness and swelling around it, and it can become quite painful if it ruptures. Cysts don’t always need treatment, but ones that grow, become infected, or bother you can be surgically removed.
Swollen Lymph Nodes
Your armpits contain a dense cluster of lymph nodes, small filtering stations that trap bacteria and viruses as part of your immune response. When your body is fighting an infection, these nodes swell and become noticeable. A swollen lymph node typically feels like a smooth, somewhat rubbery lump deeper under the skin than a pimple or cyst would be.
Common triggers include the flu, mononucleosis, and even a minor cut or skin infection on your hand or arm. The swelling usually goes down on its own once the underlying infection resolves. Autoimmune conditions like lupus can also cause chronically swollen lymph nodes in the armpits.
Lipomas
A lipoma is a slow-growing lump of fatty tissue that sits between the skin and the underlying muscle. It feels soft and doughy, moves easily when you press on it, and is almost always painless. Lipomas are benign and don’t require treatment unless they grow large enough to press on nearby nerves or simply bother you cosmetically. They can show up anywhere on the body, but the armpit is a common spot.
Contact Dermatitis From Deodorants
If you’re seeing a rash of small, itchy bumps rather than a single lump, the culprit may be your deodorant or antiperspirant. Fragrances and preservatives in these products are among the most common causes of allergic contact dermatitis. The reaction can appear as red, raised bumps, sometimes with flaking or a burning sensation, and it typically shows up within a day or two of exposure.
Switching to a fragrance-free, hypoallergenic product usually resolves things within a week. If the rash is intense, an over-the-counter hydrocortisone cream can help calm it down while the skin heals.
Hidradenitis Suppurativa
If you get painful bumps under your arms that keep coming back, hidradenitis suppurativa (HS) is worth knowing about. This is a chronic skin condition where hair follicles become deeply blocked and inflamed, producing painful nodules, abscesses, and sometimes tunnels under the skin that drain fluid. It tends to affect areas where skin rubs together, so the armpits, groin, and under the breasts are the most common locations.
Doctors diagnose HS when someone has typical lesions (deep nodules, abscesses, or scarring) in these skin-fold areas, with at least two flare-ups over six months. The condition is classified in three stages:
- Stage I: Isolated abscesses without scarring or tunnels under the skin.
- Stage II: Recurrent abscesses with some scarring and connecting tunnels.
- Stage III: Widespread, interconnected abscesses and tunnels across the entire area.
HS is often misdiagnosed as ordinary boils for years before someone gets the correct diagnosis. If your armpit bumps leave scars, drain on their own, or appear in the same spots repeatedly, bringing up HS with a dermatologist can save you a lot of time.
Red Flags Worth Paying Attention To
The vast majority of armpit bumps are benign. But certain characteristics raise concern about something more serious, including lymphoma or breast cancer. Any armpit node you can feel that isn’t clearly tied to an infection warrants a closer look, regardless of size.
Features that are particularly concerning: a lump that feels hard or rock-like rather than soft or rubbery, one that doesn’t move when you press on it (meaning it’s fixed to the tissue underneath), a lump larger than about 2 centimeters (roughly the size of a grape), or one that keeps growing over weeks. Unexplained weight loss, night sweats, or persistent fatigue alongside the lump are additional warning signs. A lump that drains pus or fluid is more likely an infection or HS than cancer, but persistent drainage also deserves medical attention.
A good general rule: if an armpit bump doesn’t shrink or resolve within two weeks, is growing, or is painless but hard, it’s worth getting checked. Most of the time the answer will be reassuring, but these features are exactly the ones doctors are trained to evaluate quickly.