Bumps under your armpits usually come from one of a handful of causes: infected hair follicles, ingrown hairs, swollen lymph nodes, cysts, or a chronic skin condition called hidradenitis suppurativa. The armpit is especially prone to these problems because it combines hair follicles, sweat glands, lymph nodes, and constant friction in a warm, moist environment. Most armpit bumps are harmless and resolve on their own, but some patterns deserve attention.
Infected Hair Follicles (Folliculitis)
The most common reason for small, pimple-like bumps in your armpit is folliculitis, an infection of the hair follicles. It shows up as clusters of small bumps or pus-filled blisters around individual hairs, often itchy or tender. The skin may feel warm to the touch. The usual culprit is Staphylococcus aureus, the same staph bacteria behind most skin infections.
Shaving is a major trigger. A razor creates tiny nicks in the skin that let bacteria in, especially if the blade is dull or you’re shaving dry skin. Tight clothing that traps sweat and rubs against the area makes things worse. Mild folliculitis often clears up within a week or two with basic hygiene: keeping the area clean, avoiding further shaving until it heals, and using a benzoyl peroxide 5% wash for five to seven days. Persistent cases may need a prescription topical antibiotic.
Ingrown Hairs
Ingrown hairs happen when a shaved or tweezed hair curls back into the skin instead of growing outward. The result is a firm, sometimes painful bump that can look red or darkened. It’s easy to confuse with folliculitis, and in fact an ingrown hair can become infected and turn into folliculitis.
To prevent them, shave with warm, wet skin and a shaving gel or cream. Use a single-blade razor, shave in the direction the hair grows, and rinse the blade after every stroke. Replace razors frequently. If you’re getting ingrown hairs repeatedly, consider switching to an electric shaver held just above the skin’s surface, or a depilatory cream that dissolves hair chemically without cutting it. Gentle exfoliation with a washcloth or scrub in small circular motions helps free trapped hairs before they become a problem.
Swollen Lymph Nodes
Your armpits contain a dense cluster of lymph nodes, small bean-shaped glands that filter fluid and fight infection. When your immune system is active, these nodes can swell into noticeable, tender lumps. Infections or injuries anywhere in your arms, hands, chest, or upper body commonly cause this because lymph fluid from those areas drains through the armpit.
A cold, a cut on your hand, or even a recent vaccination can trigger the swelling. During clinical trials for the Moderna mRNA vaccine, about 12% of adults under 65 reported armpit swelling or tenderness after the first dose, and 16% after the second. For the Pfizer vaccine, less than 1% reported palpable swelling, though imaging studies suggest the true rate is much higher. Vaccine-related lymph node swelling typically appears two to four days after the shot and lasts around 10 days, though imaging studies have found it can take an average of about four months to fully resolve.
Reactive lymph nodes from everyday infections are soft, movable, and tender. They shrink back to normal once the underlying cause resolves.
Contact Dermatitis From Deodorant
If your armpit bumps come with widespread redness, itching, or a rash rather than individual lumps, your deodorant or antiperspirant may be the problem. Fragrance chemicals are the most frequent offenders. Ingredients like isoeugenol, hydroxycitronellal, and cinnamic aldehyde are well-documented skin sensitizers found in many conventional and “natural” deodorants alike. Aluminum salts, the active ingredient in antiperspirants that blocks sweat glands, can also cause irritation in some people.
The tricky part is that you can develop a sensitivity to a product you’ve used for years. If you suspect contact dermatitis, stop using the product for two weeks and see if the bumps clear. Switching to a fragrance-free formula is the simplest first step.
Hidradenitis Suppurativa
If you keep getting painful, deep bumps in your armpits that come back in the same spots, you may have hidradenitis suppurativa (HS). This chronic inflammatory condition affects roughly 1% of the global population and is often misdiagnosed for years as recurring boils or ingrown hairs. It targets areas where skin rubs together: armpits, groin, under the breasts, and inner thighs.
HS starts with painful firm nodules that can develop into abscesses. In its earliest stage, you get single or multiple abscesses without permanent scarring. Over time, if the condition progresses, it can form tunnels under the skin (sinus tracts) that drain fluid, along with permanent scarring. Once scarring develops, it doesn’t reverse with medication, which is why early recognition matters.
The condition is more common in women, people who smoke, and those with obesity, though it can affect anyone. If you notice recurring painful lumps in the same areas every few weeks or months, especially if they sometimes drain thick fluid, bring it up with a dermatologist specifically. Many people go through multiple doctors before getting the correct diagnosis.
Cysts and Lipomas
A single, persistent bump that doesn’t seem infected could be a cyst or a lipoma. These are benign growths, but they feel quite different from each other.
- Cysts are enclosed sacs filled with fluid or semi-solid material. They feel firm, can be tender to the touch, and may become red or swollen. If a cyst ruptures, it can become suddenly painful.
- Lipomas are collections of fat cells between muscle and skin. They feel soft and doughy, move easily when you press on them, and are usually painless. Most stay small, around two inches or less in diameter.
Neither type is dangerous on its own, but both can be removed if they’re uncomfortable or growing. A cyst that gets repeatedly infected may be worth removing to prevent future flare-ups.
When Armpit Bumps Need Medical Attention
Most armpit bumps are benign, but certain features are red flags. A lump that feels hard, doesn’t move when you push on it, and is painful could signal something more serious. Cancerous lumps in the armpit tend to be firm, fixed in place, and painless or painful depending on the type. Breast, lung, thyroid, and skin cancers (particularly melanoma) can all spread to the armpit lymph nodes.
You should have an armpit lump evaluated if it doesn’t go away after two weeks, feels hard and immovable, keeps getting bigger, grows back after being removed, or comes with a fever. A lump that suddenly becomes tender when it wasn’t before also warrants a visit. Silicone breast implants can occasionally cause armpit lymph node swelling from low-level inflammation, which can mimic more concerning conditions on imaging.
For the vast majority of people, armpit bumps come down to shaving irritation, a reactive lymph node, or a product sensitivity. Adjusting your shaving technique, switching deodorants, or simply waiting a couple of weeks resolves most cases without any treatment at all.