A swollen shoulder usually means something inside the joint is inflamed, injured, or accumulating excess fluid. The most common culprits are bursitis, tendon injuries, and arthritis, though infections and fractures can also cause visible swelling. The location of the swelling, how quickly it appeared, and whether you have other symptoms like fever or inability to move your arm all help narrow down the cause.
Bursitis: The Most Common Cause
Your shoulder contains small fluid-filled sacs called bursae that cushion the space between bones, tendons, and muscles. When the bursa just below the top of your shoulder (the subacromial bursa) becomes irritated, it fills with extra fluid and swells. This is called bursitis, and it’s one of the most frequent reasons for a visibly puffy shoulder.
Subacromial bursitis causes pain in the upper shoulder or upper third of the arm, and the pain is often severe when you try to move the joint. The swelling tends to sit right on top of the shoulder, and the area may feel warm to the touch. Repetitive overhead motions, like painting a ceiling or throwing a ball, are classic triggers. Bursitis can also develop after a direct blow to the shoulder or from prolonged pressure on the joint.
Tendon Injuries and Rotator Cuff Problems
The rotator cuff is a group of four muscles and tendons that wrap around your shoulder joint and hold it in place. These tendons can become inflamed (tendinitis) or partially or fully torn, and both situations produce swelling. Rotator cuff tendinitis causes a deep, dull ache in the shoulder along with difficulty sleeping on the affected side and pain when lifting your arm overhead. The onset can be sudden or gradual.
A rotator cuff tear, especially an acute one from a fall or heavy lift, typically causes more dramatic swelling and weakness. You may notice that you can’t raise your arm at all, or that it feels unstable. Unlike bursitis, which tends to swell near the surface, rotator cuff injuries often produce a deeper ache with swelling that’s harder to pinpoint visually. Injuries can range from mild inflammation to a complete tendon tear, and the severity of your swelling generally tracks with the severity of the damage.
Arthritis and Fluid Buildup
If your shoulder swelling came on gradually over weeks or months, arthritis is a likely explanation. Osteoarthritis wears down the cartilage inside the joint, which triggers chronic inflammation. That inflammation causes the joint lining to produce excess fluid, a condition called joint effusion. The shoulder looks puffy and feels stiff, particularly in the morning or after periods of inactivity.
Rheumatoid arthritis and gout can also cause shoulder effusion, though gout affects the shoulder less often than smaller joints. With osteoarthritis, the swelling tends to come and go but may become a recurring part of life. Rheumatoid arthritis is more likely to affect both shoulders and other joints simultaneously.
Trauma: Falls, Fractures, and Dislocations
A shoulder that swells rapidly after an injury, like a fall onto an outstretched hand or a direct impact during sports, could involve a fracture, dislocation, or significant soft tissue damage. Fractures of the collarbone or upper arm bone cause immediate, widespread swelling along with sharp pain and sometimes visible deformity. A dislocated shoulder looks obviously out of place, with the arm hanging at an unusual angle.
Even without a fracture, a hard impact can cause bleeding inside the joint (hemarthrosis), which fills the space with blood and makes the shoulder balloon quickly. If your shoulder swelled within minutes of an injury and you can’t move it, that’s a strong signal of a serious structural problem that needs imaging right away.
Infection in the Joint
An infected shoulder joint (septic arthritis) is uncommon but serious. The hallmarks are swelling combined with excessive warmth at the site, significant tenderness, fever, and feeling generally unwell. The redness and swelling may spread up or down your arm rather than staying localized. Septic arthritis can develop after a skin wound near the shoulder, after a joint injection, or when bacteria travel through the bloodstream from an infection elsewhere.
Diagnosing a shoulder infection can be tricky. In one study of shoulder joint fluid samples, 57% had cell counts below the threshold typically used to confirm infection in other joints, meaning standard lab cutoffs don’t always apply here. If you have a hot, swollen shoulder along with fever or chills, seek care promptly. Untreated joint infections can cause permanent cartilage damage within days.
Less Common Causes
Paralabral cysts are fluid-filled sacs that form near the cartilage ring (labrum) lining the shoulder socket, usually linked to a labral tear. These cysts are rare, with an estimated incidence around 0.6%, and they primarily affect young, active men. A paralabral cyst can press on nearby nerves, causing numbness over the outer shoulder, weakness in the arm, and a dull ache that doesn’t match any obvious injury. In some cases, cysts appear without any identifiable trauma.
Other uncommon causes of shoulder swelling include tumors (both benign and malignant), blood clots in the arm veins, and allergic reactions. These are far less likely than the causes above but worth considering if your swelling doesn’t fit the usual patterns or doesn’t respond to basic treatment.
How Shoulder Swelling Is Diagnosed
Your doctor will start with a physical exam, checking your range of motion, the exact location of swelling, and whether the skin is warm or red. Standard X-rays are usually the first imaging step to rule out fractures and look for signs of arthritis.
For soft tissue problems like bursitis, tendon tears, or fluid collections, the two main tools are ultrasound and MRI. Ultrasound is cheaper, lets the examiner watch your shoulder move in real time, and can guide a needle directly into a swollen bursa to drain fluid. However, it depends heavily on the skill of the person performing it and can’t see as deeply into the joint. MRI provides more detailed images of tendons, cartilage, and bone and is considered the gold standard for surgical planning. A large meta-analysis of 144 studies found MRI detects rotator cuff tears with higher sensitivity (84% vs. 81%) and specificity (86% vs. 82%) compared to ultrasound. For full-thickness tears, that gap widens further, with MRI catching 91% of tears versus 87% for ultrasound.
If infection is suspected, a needle aspiration of the joint fluid is essential. The fluid is sent for cell counts and bacterial cultures to confirm or rule out septic arthritis.
Managing Swelling at Home
For non-traumatic shoulder swelling without signs of infection, the initial approach is straightforward: rest the joint, apply ice for 15 to 20 minutes several times a day, and avoid the movements that aggravate it. Ice works best in the first 48 to 72 hours when inflammation is peaking. Over-the-counter anti-inflammatory medications can help reduce both swelling and pain.
Heat can feel soothing for stiff, achy shoulders, but use it cautiously when swelling is present. Warmth increases blood flow and relaxes muscles, which helps with stiffness. It can also worsen inflammation and fluid buildup. A reasonable approach is to stick with ice during the acute swollen phase and introduce gentle heat once the swelling starts to settle.
Avoid immobilizing your shoulder completely for more than a few days. Prolonged stillness leads to stiffness and muscle loss, which can make recovery harder. Gentle pendulum exercises, where you lean forward and let your arm hang and swing in small circles, keep the joint mobile without loading the injured structures.
Signs That Need Immediate Attention
Certain combinations of symptoms point to problems that shouldn’t wait. A shoulder that is swollen, hot, and red, especially with fever, suggests infection. Swelling that appeared instantly after trauma with an inability to move the arm could mean a fracture or dislocation. Swelling that spreads visibly up or down your arm, numbness or tingling in your hand, or swelling in multiple joints at once are all reasons to get evaluated quickly. If your shoulder swelling has been gradually worsening despite rest, ice, and anti-inflammatory medication over two to three weeks, that also warrants a medical evaluation to identify the underlying cause and start targeted treatment.