Fluid leaking from your armpit usually comes from one of a handful of causes: excessive sweating, an infected cyst or abscess, a chronic skin condition, irritated skin folds, or post-surgical fluid buildup. The type of fluid, its color, and any accompanying symptoms like pain or fever can help narrow down what’s going on. Most causes are treatable, but some need prompt medical attention.
Excessive Sweating (Hyperhidrosis)
If the “leak” is watery and clear, you may be dealing with hyperhidrosis, a condition where your sweat glands produce far more fluid than your body needs to cool itself. The armpits are one of the areas with the highest concentration of sweat glands, which is why they’re a common trouble spot. In people with hyperhidrosis, the sympathetic nervous system releases too much of a chemical messenger called acetylcholine, overstimulating sweat production. A feedback loop that normally tells the brain “we’ve cooled down enough” appears to be impaired, so the sweating keeps going even when temperature regulation doesn’t call for it.
Hyperhidrosis can be triggered by physical activity, heat, or stress, but it also occurs without any obvious trigger. If you’re soaking through shirts regularly or noticing dripping that goes beyond normal perspiration, this is worth bringing up with a doctor. Treatments range from prescription-strength antiperspirants to procedures that target the overactive sweat glands.
Infected Cysts and Abscesses
A lump in your armpit that starts draining thick, cloudy, or foul-smelling fluid is likely an abscess or an infected cyst. Sebaceous cysts in the armpit are usually painless until they get infected. At that point, the cyst becomes a tender, swollen mass filled with thick, cheesy material that can rupture and leak. Abscesses form when bacteria invade the skin, often through a nick from shaving or a blocked sweat gland, and create a pocket of pus.
Antibiotics alone typically aren’t enough to resolve an abscess. The standard treatment is incision and drainage, where a doctor opens the abscess, expresses the pus, and irrigates the cavity with sterile saline. For smaller collections, manual expression plus antibiotics may be sufficient. Many of these infections are caused by staph bacteria, and drug-resistant strains (MRSA) are increasingly common, which is why your doctor may culture the fluid to guide treatment. You’ll usually have a follow-up visit two to three days after drainage, and the wound heals on its own from the inside out over the following weeks.
Hidradenitis Suppurativa
If you’re getting recurring painful lumps in your armpit that drain fluid, come back in the same spot, or leave scars, you may have hidradenitis suppurativa (HS). This chronic inflammatory condition produces deep-seated nodules, typically half a centimeter to two centimeters in size, that persist for days to months. They’re frequently mistaken for boils, but unlike a one-time boil, HS lesions recur, can rupture on their own, and sometimes form tunnels under the skin that connect multiple lumps.
The fluid from HS lesions is often a mixture of blood and clear fluid (serosanguinous), though it can become thick and foul-smelling if bacteria colonize the area. Diagnosis is based entirely on what the lesions look like, where they appear (armpits, groin, under the breasts), and whether they keep coming back. Unfortunately, the average delay in getting an HS diagnosis is about seven years because it looks so much like other conditions early on. If you’ve been told repeatedly that you “just get boils” in your armpits, it’s worth asking specifically about HS.
Weeping Skin From Intertrigo
Sometimes the fluid isn’t coming from a lump at all. Instead, the skin itself looks raw, bright red, and wet. This is intertrigo, an irritation caused by moisture, friction, bacteria, or fungus trapped in the skin folds of the armpit. The affected area develops well-defined, weeping patches that can sting or burn. It’s more common in warm weather, in people with larger skin folds, or when sweat doesn’t evaporate properly.
Intertrigo caused by yeast (candida) often has a telltale appearance: a vivid red rash with smaller “satellite” spots around the edges. Bacterial intertrigo may produce more of a yellowish weeping. Keeping the area dry, wearing breathable fabrics, and using barrier creams or antifungal treatments typically clear it up, though it tends to come back if the underlying moisture problem isn’t managed.
Post-Surgical Fluid (Seroma)
If you’ve recently had surgery near or in your armpit, such as a mastectomy, lymph node biopsy, or even a cosmetic procedure, a pocket of clear yellow fluid called a seroma is a common cause. Seromas typically appear 7 to 10 days after surgery or after a surgical drain is removed. You’ll notice a soft, fluid-filled swelling near the incision site.
Small seromas often resolve on their own as the body reabsorbs the fluid. Larger ones, generally those holding more than 75 to 100 milliliters, can cause pain, limit your shoulder movement, and raise your risk of infection. These usually need to be drained with a needle, sometimes more than once. If you’re recovering from surgery and notice a growing, tender swelling in your armpit, contact your surgical team.
What the Color of the Fluid Tells You
The appearance of the fluid is one of the most useful clues to what’s causing it:
- Clear or pale yellow and watery: This is serous fluid, made mostly of plasma. It’s common in normal wound healing, seromas, and minor skin irritation. On its own, it’s usually not alarming.
- Pink or light red and thin: Serosanguineous drainage is a mix of plasma and a small amount of blood. It’s the most common type of wound drainage and is normal after surgery or in conditions like HS.
- Bright red: This is active bleeding. Small amounts right after an injury or procedure are expected, but ongoing bright red drainage needs medical evaluation.
- Thick, white, yellow, green, or brown: Purulent drainage contains white blood cells, bacteria, and dead tissue. It almost always signals an infection and needs prompt attention, especially if it smells foul.
Signs That Need Urgent Attention
Most causes of armpit fluid leaking are manageable, but certain symptoms suggest something more serious is happening. Red streaks spreading outward from the area, a fever, rapid heart rate, confusion, or extreme pain can be signs that a local infection is becoming systemic. Sepsis is a medical emergency that develops when infection spreads into the bloodstream, and it can escalate quickly.
Swollen lymph nodes in the armpit that feel hard or rubbery, don’t move when you push on them, and are growing rapidly deserve a medical evaluation, particularly if they’re accompanied by unexplained weight loss, night sweats, or persistent fevers. These features can sometimes point to lymphoma or other cancers, though the vast majority of swollen armpit lymph nodes are caused by infections or immune responses and resolve on their own. The distinction matters enough to get checked.