Recurring bumps under your armpit usually come from one of a handful of causes: irritated hair follicles, clogged sweat glands, allergic reactions to deodorant, swollen lymph nodes, or a chronic skin condition called hidradenitis suppurativa. The armpit is especially prone to bumps because it combines hair, sweat glands, friction from skin rubbing together, and daily exposure to products like deodorant and razors. Figuring out which cause matches your symptoms is the first step toward making them stop.
Folliculitis and Ingrown Hairs
The most common reason for armpit bumps is folliculitis, an infection or irritation of the hair follicles. These bumps tend to be small, red, and sometimes filled with pus. They look a lot like pimples and often appear a day or two after shaving. Ingrown hairs are a specific type of folliculitis where a shaved hair curls back into the skin instead of growing outward, creating a tender bump around the follicle.
If you shave your armpits regularly, this is the most likely explanation for recurring bumps. Shaving creates tiny nicks in the skin and cuts hairs at sharp angles that make them more likely to grow inward. A few changes can make a real difference: shave at the end of your shower (warm water loosens the hair and causes it to swell, so it’s less likely to curve back into the skin), always use a moisturizing shaving cream, and shave in the direction your hair grows. Replace disposable razors every five to seven shaves, and store them somewhere dry so bacteria don’t build up on the blade. After shaving, rinse with warm water and press a cool, damp washcloth against the skin to calm inflammation.
When folliculitis bumps get larger, deeper, and more painful, they can become boils. A boil is essentially a deeper infection of the follicle that fills with pus. You’ll feel a warm, painful lump under the skin, sometimes with whitish or bloody fluid leaking from the center. Most boils drain and heal on their own within a couple of weeks. If several boils cluster together, that’s called a carbuncle, and it can come with fever and fatigue, which signals a more serious infection.
Deodorant and Product Reactions
If your bumps are itchy, rashy, or appear across a broad area rather than centered on individual hair follicles, the culprit may be your deodorant or antiperspirant. This type of reaction is contact dermatitis, and it’s surprisingly common. A review of 107 deodorant and antiperspirant products found that 97 of them contained fragrance, making it the single most common allergen in these products. The specific compounds most often responsible are geraniol, eugenol, and hydroxycitronellal, all found in fragrance blends.
The second most common allergen is propylene glycol, a solvent used in nearly half of the products reviewed. Essential oils (including ylang-ylang and lemongrass oil), parabens, vitamin E, and lanolin can also trigger reactions, though they appear in fewer products. If you suspect your deodorant is the problem, switching to a fragrance-free, propylene glycol-free formula is the simplest test. Stop using the product for a week or two and see if the bumps clear. If they do, you have your answer.
Cysts Under the Skin
Cysts feel different from folliculitis bumps. They’re typically round, firm, slow-growing lumps that sit beneath the skin and move slightly when you press on them. The type most often found in the armpit is an epidermoid cyst (sometimes called a sebaceous cyst, though that name is technically inaccurate). These form when skin cells that normally shed to the surface instead get trapped below the skin, creating a pocket filled with a soft, cheese-like protein called keratin.
Epidermoid cysts are benign. They can sit under your skin for months or years without causing problems. They become an issue when they get infected or inflamed, turning red, swollen, and painful. A dermatologist can drain or remove a cyst if it’s bothering you, but squeezing one yourself risks pushing the contents deeper and causing infection.
Swollen Lymph Nodes
Your armpits contain a cluster of lymph nodes, small glands that filter fluid and help fight infections. When your immune system is active, these nodes can swell and feel like soft, tender bumps. Common triggers include a cold, a skin infection on your hand or arm, or a recent vaccination. Swollen lymph nodes from a COVID-19 vaccine, for example, typically appeared about seven days after the shot, and most resolved within 30 to 45 days, though some cases took several months to fully return to normal size.
Reactive lymph nodes are usually smooth, movable, and tender. They swell in response to something and shrink once the trigger resolves. A lymph node that is hard, fixed in place (doesn’t move when pressed), painless, or keeps growing over weeks without an obvious cause is worth getting evaluated promptly, especially if you also notice unexplained weight loss or night sweats.
Hidradenitis Suppurativa
If you’ve been getting painful, deep bumps in your armpits for months or years, and they keep coming back in the same areas, you may have hidradenitis suppurativa (HS). This is a chronic inflammatory condition that affects the hair follicles in areas where skin rubs together: armpits, groin, buttocks, and under the breasts. It typically starts with a single painful lump under the skin that lasts for weeks or months. Over time, more bumps develop. Some break open and drain pus with a noticeable odor. Wounds can heal but leave thick, ropelike scars or pitted skin that eventually restricts movement.
HS affects anywhere from less than 1% to about 4% of the population depending on geography and how studies define it. It’s frequently misdiagnosed as ordinary boils or ingrown hairs, so many people go years before getting the right diagnosis. The key difference is the pattern: HS bumps recur in the same locations, often leave tunnels or scars beneath the skin, and don’t respond to basic hygiene changes.
Treatment depends on severity. For mild cases, a dermatologist may prescribe a topical antibiotic like clindamycin to reduce lumps and manage infection, or a resorcinol cream that opens clogged follicles and reduces inflammation. When the condition is more widespread, oral antibiotics, hormonal therapy (including certain birth control pills or other hormone-modifying medications), or biologic medications may be recommended. The FDA has approved several biologics specifically for moderate-to-severe HS, and these can significantly reduce flare-ups for people who haven’t responded to other treatments.
When a Bump Needs Prompt Attention
Most armpit bumps are benign, but certain features should move up your timeline for getting one checked. A lump that is hard, irregularly shaped, fixed to the tissue beneath it, or growing steadily over weeks is worth evaluating. An armpit lump paired with a breast lump raises suspicion for breast cancer and needs thorough assessment. Other concerning signs include skin tethering (where the skin over the lump dimples or pulls inward), bloody nipple discharge, or a rapidly enlarging mass. These features don’t guarantee something serious, but they do warrant imaging or a biopsy rather than watchful waiting.
For the more common causes, keeping the area clean and dry, avoiding irritating products, and adjusting your shaving routine will resolve most bumps within a week or two. If bumps keep returning despite those changes, a dermatologist can examine the pattern and determine whether you’re dealing with something that needs targeted treatment.