Shoulder bursitis happens when a small, fluid-filled sac called the bursa becomes inflamed, usually because it’s being repeatedly pinched or irritated between the bones and tendons in your shoulder joint. The most common cause is impingement, where the bursa gets compressed during overhead arm movements, but injuries, infections, and underlying health conditions can also trigger it. Shoulder pain affects up to 26% of people at any given time, and bursitis is one of the most frequent culprits.
How the Shoulder Bursa Gets Compressed
Your shoulder has a narrow gap called the subacromial space, sitting between the ball of the upper arm bone and a bony roof called the acromion. A bursa lives in that gap, acting as a cushion so tendons can glide smoothly when you move your arm. When you raise your arm overhead, that space narrows. If something causes it to narrow too much or too often, the bursa and nearby tendons get squeezed.
This compression is called subacromial impingement, and it’s the single most common pathway to shoulder bursitis. Each time the bursa is pinched, it swells a little. Over time, the swelling itself takes up space, making the pinching worse, which creates a cycle of worsening inflammation. That’s why shoulder bursitis often starts as a mild ache and gradually becomes more painful over weeks or months.
Repetitive Overhead Motions
The trigger for most cases is doing the same shoulder movement over and over, especially movements that involve force. Swinging a hammer, throwing a ball, rowing, and swinging a bat, golf club, or tennis racket are all classic causes. Any motion that repeatedly lifts your arm above shoulder height compresses the bursa in that narrow subacromial space.
Occupational data from the CDC shows a clear dose-response relationship: for every 1,000 hours of work with your hands at or above shoulder level, the risk of shoulder disorders including bursitis rises by about 21%. That means a doubling of risk at roughly 3,600 hours of overhead work. Painters, carpenters, landscapers, plumbers, and warehouse workers face particularly high rates. Production workers in meat processing, garment manufacturing, and auto assembly have more than double the risk of shoulder impingement compared to office staff.
You don’t need to be doing heavy labor for this to happen. Any sustained overhead positioning counts. Stocking high shelves, washing windows, or even sleeping with your arm overhead every night can contribute if the motion is frequent enough.
Your Bone Shape Matters
Not everyone who does overhead work develops bursitis, and part of the reason is anatomy. The acromion, that bony roof over the bursa, comes in different shapes. Orthopedic classification identifies three types: flat, curved, and hooked. A hooked acromion (Type III) leaves less room in the subacromial space, which means the bursa gets compressed more easily during normal movements. Some people also have an extra bone fragment in the acromion called an os acromiale, which can create a similar narrowing effect.
These variations are things you’re born with. If you have a hooked acromion and you also do overhead work or sports, your risk compounds. It also helps explain why two people with the same job can have very different outcomes.
Acute Injuries and Falls
While most shoulder bursitis develops gradually, a single traumatic event can cause it too. Falling onto an outstretched arm, taking a direct blow to the shoulder, or suddenly lifting something much heavier than expected can damage the bursa in one incident. The bursa responds to the trauma by filling with extra fluid and becoming inflamed. This type of bursitis tends to come on quickly, with noticeable swelling and pain within hours to days of the injury, rather than the slow buildup seen with repetitive strain.
Infections in the Bursa
Septic bursitis is a less common but more serious cause. Bacteria can enter the bursa through a cut, scrape, or puncture wound near the shoulder, or occasionally through the bloodstream from an infection elsewhere in the body. Over 80% of septic bursitis cases are caused by Staphylococcus aureus and other gram-positive bacteria, though fungal infections and other organisms can be responsible in rarer cases.
Septic bursitis feels different from the mechanical kind. It typically involves redness and warmth over the shoulder, significant swelling, fever, and pain that feels more intense and constant rather than movement-related. Physical activities that expose the shoulder to scrapes or dirty environments increase susceptibility, and people with weakened immune systems face greater risk of complications.
Underlying Health Conditions
Several systemic conditions make bursitis more likely. Rheumatoid arthritis causes widespread joint inflammation that can affect the bursa directly. Gout, where crystal deposits form in and around joints, can irritate the bursa and trigger episodes of acute inflammation. Diabetes also raises the risk, likely through its effects on tissue health, blood flow, and the body’s inflammatory response.
When bursitis stems from one of these conditions, it may show up alongside joint problems in other parts of the body. It also tends to recur more easily, since the underlying inflammation never fully resolves even when the shoulder improves temporarily.
Age and Long-Term Wear
Shoulder bursitis becomes significantly more common after age 50. A systematic review of shoulder pain studies found that 16 out of 21 studies reported higher rates and risk in older participants. This reflects decades of cumulative wear on the rotator cuff tendons and bursa, along with age-related changes like reduced blood supply to the tendons and gradual bone spur formation on the acromion. These spurs further narrow the subacromial space, making impingement more likely even during everyday activities like reaching into a cabinet or putting on a jacket.
Women in physically demanding jobs appear to face particular risk. Research on production workers found a more than twofold increased risk among female workers compared to non-production staff, suggesting that differences in shoulder anatomy, muscle mass, or hormonal factors may play a role alongside occupational demands.
Why It Often Involves More Than One Cause
In practice, shoulder bursitis rarely has a single, clean explanation. A 55-year-old carpenter with a hooked acromion and early arthritis is dealing with at least three overlapping factors: repetitive strain, anatomical predisposition, and age-related changes. Someone with diabetes who takes a fall may develop bursitis faster and recover more slowly than someone without that underlying condition.
Understanding which causes apply to your situation matters because it shapes what’s likely to help. Bursitis from a one-time injury may resolve with rest and time. Bursitis driven by repetitive overhead work will return unless the movement pattern changes. And bursitis connected to rheumatoid arthritis or gout typically requires managing the systemic condition, not just the shoulder, to prevent flare-ups.