Armpit pain is usually caused by something minor, like a pulled muscle, an irritated hair follicle, or a reaction to your deodorant. Less commonly, it can signal swollen lymph nodes, a skin condition, or nerve compression. The location makes it easy to worry about, but most causes resolve on their own or with simple treatment.
Muscle Strain
The muscles of your chest and upper arm overlap in the armpit area, so a strain in your pectoralis (chest muscle) or latissimus dorsi (the large back muscle that wraps under your arm) can feel like armpit pain even though the injury is nearby. This is one of the most common causes, especially if you’ve recently lifted something heavy, started a new workout, or done repetitive overhead movements.
Muscle-related pain tends to be constant rather than coming and going. It usually stays in one spot instead of radiating outward, feels worse when you press on it, and flares up with specific movements like reaching overhead, pushing, or pulling. You might also notice tenderness, mild swelling, or bruising. If you can reproduce the pain by moving your arm a certain way, a strained muscle is the most likely explanation.
Skin Irritation and Contact Dermatitis
Your armpit is warm, moist, and frequently exposed to products, making it especially prone to irritation. Razor burn from dull blades or dry shaving is a common culprit, but so is an allergic reaction to something you’re applying daily.
Deodorants and antiperspirants contain several ingredients known to trigger contact dermatitis. Fragrances are the most frequent offenders, with specific compounds like hydroxycitronellal, eugenol, and geraniol among the worst. Propylene glycol, a solvent and moisturizer found in many formulas, is the second most common contact allergen in deodorants. Aluminum compounds (the active ingredient in antiperspirants), lanolin, essential oils, and parabens can also cause reactions. The result is redness, burning, itching, or soreness that stays confined to the area where the product touches your skin.
If you suspect your deodorant, try switching to a fragrance-free, minimal-ingredient formula for two to three weeks. If the pain and irritation clear up, you’ve found your answer.
Swollen Lymph Nodes
Your armpits contain a dense cluster of lymph nodes, small bean-shaped glands that filter fluid and help fight infection. When your body is fighting off a cold, a skin infection on your arm, or even recovering from a vaccination, these nodes can swell and become tender. This is the most common reason people notice a painful lump in the armpit, and it usually resolves within a couple of weeks as the infection clears.
Swollen lymph nodes from infection tend to feel soft, movable, and tender to the touch. Nodes associated with cancer behave differently: they tend to be hard, painless or painful, and fixed in place (they don’t move easily when you press on them). A lump that doesn’t go away after two weeks, keeps getting bigger, feels hard, or comes with unexplained fever, night sweats, or weight loss warrants a visit to your doctor.
Skin Infections and Yeast Overgrowth
The warm, damp environment of the armpit is ideal for bacteria and yeast. A small nick from shaving can let bacteria in, leading to an infected hair follicle (folliculitis) that presents as a red, painful bump. Yeast infections caused by Candida can also develop in the armpit folds, producing a red, itchy, sometimes burning rash.
A related condition called intertrigo happens when skin-on-skin friction combines with trapped moisture. The skin becomes raw, red, and sore, and it can worsen quickly if yeast or bacteria move in. Keeping the area dry, wearing breathable fabrics, and using antifungal or barrier creams typically clears it up.
Hidradenitis Suppurativa
If you get recurring, deep, painful lumps in your armpit that last for weeks or months, hidradenitis suppurativa (HS) could be the cause. This chronic inflammatory condition targets hair follicles in areas with sweat glands, and the armpit is one of the most common sites. It usually starts with a single painful, pea-sized lump under the skin that doesn’t behave like a normal pimple.
Over time, more bumps may form. Some break open and drain pus or blood, sometimes with a noticeable odor. In advanced cases, tunnels can form under the skin connecting the lumps, and these wounds heal slowly if at all. Blackheads appearing in pairs are another hallmark sign. HS is often mistaken for boils or ingrown hairs early on, which delays diagnosis. If you notice a pattern of recurring deep lumps in your armpits, groin, or buttocks, it’s worth bringing up with a dermatologist.
Hormonal and Breast-Related Pain
Breast tissue doesn’t stop neatly at the edge of your breast. A portion called the tail of Spence extends up into the armpit, and this tissue responds to the same hormonal fluctuations as the rest of your breast. Many women notice armpit soreness that comes and goes with their menstrual cycle, particularly in the days before a period. This cyclical pain is a normal response to hormonal shifts.
During pregnancy and breastfeeding, armpit breast tissue can swell significantly due to engorgement, sometimes catching women off guard because they don’t associate the armpit with breast tissue. This is a normal variant and not a sign of disease, though the swelling and pain can be uncomfortable.
Nerve Compression
A network of nerves called the brachial plexus runs through the armpit on its way from the neck to the arm and hand. When these nerves get compressed, the pain can feel like it originates in the armpit itself. Key signs that point to nerve involvement include tingling, burning, or numbness that extends into the shoulder, arm, or hand, along with weakness in your grip or difficulty raising your arm.
A related condition, thoracic outlet syndrome, occurs when blood vessels and nerves in the upper armpit get compressed between bones. This can cause pain, swelling, or a feeling of heaviness in the arm. Nerve-related armpit pain typically has a distinct quality: burning, electric, or “pins and needles” rather than the dull ache of a muscle strain or the sharp tenderness of an inflamed lymph node.
Heart-Related Pain
Pain in the left armpit can occasionally be referred pain from the heart, particularly during angina or a heart attack. Cardiac pain typically feels like pressing, burning, or squeezing centered under the breastbone, and it can spread into the jaw, throat, left arm, or sometimes both arms. It does not usually present as armpit pain alone.
If armpit or left arm pain comes on suddenly and is accompanied by chest pressure, shortness of breath, nausea, or lightheadedness, treat it as a medical emergency.
When Armpit Pain Needs Attention
Most armpit pain improves within a few days to two weeks, especially if it’s tied to a muscle strain, skin irritation, or a minor infection. Signs that something more is going on include a lump that persists beyond two weeks, a lump that is hard and doesn’t move, progressive swelling, unexplained weight loss, fevers without an obvious infection, or pain accompanied by tingling and weakness radiating down your arm. A lump that grows back after draining or keeps getting bigger also deserves evaluation.