Ganglion cysts form when thick, jelly-like fluid accumulates in a sac near a joint or tendon, most often on the wrist or hand. The exact trigger isn’t fully understood, but the leading explanation centers on stress or damage to the joint capsule that allows fluid to leak into surrounding tissue.
How a Ganglion Cyst Forms
Your joints are surrounded by a tough capsule filled with synovial fluid, the slippery liquid that keeps joints lubricated. When that capsule develops a small tear, either from a sudden injury or from gradual wear over time, synovial fluid can seep out into the tissue around the joint. Once this fluid escapes, it reacts with local tissue and thickens into a gelatinous substance. A wall forms around it, and what you’re left with is a firm, round lump sitting just beneath the skin.
One important detail: ganglion cysts are not simply balloons of joint lining that have bulged outward. Researchers have noted that the cyst wall lacks the synovial lining found inside the joint itself, which means the cyst is a new structure created by the body’s reaction to leaked fluid rather than a direct extension of the joint.
Joint Stress and Repetitive Use
The most widely supported explanation for why the capsule tears in the first place is mechanical stress on the joint. This can be acute, like a sprain or impact injury, or chronic, from repetitive motions that strain the same joint over and over. Gymnasts, for example, develop wrist ganglion cysts at higher rates because of the constant load they place on their wrists. Office workers who spend hours typing or using a mouse can also be susceptible.
Pre-existing joint problems make things worse. Ligament injuries around the wrist bones can alter the way the joint moves, gradually weakening the capsule until fluid eventually leaks through. This is why ganglion cysts sometimes appear weeks or months after an injury you thought had healed. The initial damage changed the joint’s mechanics just enough to set the stage for a cyst later on.
Osteoarthritis and Joint Degeneration
Wear-and-tear arthritis is a well-established risk factor, particularly for cysts that form near the fingertips. People with osteoarthritis in the finger joints closest to the nails are at higher risk of developing what are sometimes called mucous cysts, a type of ganglion cyst specific to that location. The degenerative changes in the joint create the same kind of capsular weakness that allows fluid to escape, but in this case the underlying driver is cartilage breakdown rather than a traumatic injury.
Where Ganglion Cysts Typically Appear
The back of the wrist is by far the most common site. The front of the wrist is the second most common. Together, these two locations account for the large majority of cases. Beyond the wrist, ganglion cysts also develop at the base of the fingers on the palm side, on the top of the foot, and near the ankle or knee. Mucous cysts near the fingernail joint tend to appear in older adults with arthritis, while wrist cysts are more common in younger people.
Who Gets Them
Ganglion cysts can appear at any age, but they show up most often in women between 20 and 50. Women are about three times more likely to develop one than men. The reason for this gender difference isn’t entirely clear, though it may relate to differences in joint laxity and connective tissue structure. If you’re a younger woman who uses your hands heavily for work or sports, your risk profile is higher than average.
What’s Inside the Cyst
If you’ve ever wondered what would come out if you popped a ganglion cyst, the answer is a thick, clear, sticky fluid that looks and feels like jelly. It’s similar in composition to synovial fluid but considerably more viscous, concentrated with proteins and a lubricating compound called hyaluronic acid. This is why the cyst feels firm when you press on it rather than squishy like a blister. The fluid is not infectious or cancerous. It’s essentially a concentrated version of the same lubricant your joints produce naturally.
How They’re Identified
Most ganglion cysts are diagnosed by their appearance and feel alone. They’re typically round, smooth, and between one and three centimeters across, though some grow larger. A classic office test involves shining a light through the lump. Because the cyst is filled with clear fluid rather than solid tissue, light passes through it, confirming it’s fluid-filled. If there’s any doubt about the diagnosis, an ultrasound or MRI can confirm the cyst and reveal whether it connects to the joint or a tendon sheath underneath.
Many ganglion cysts cause no symptoms at all beyond the visible bump. When they do cause problems, it’s usually because the cyst presses on a nearby nerve, producing pain, tingling, or weakness. Cysts on the back of the wrist can limit how far you can bend the joint. Some cysts fluctuate in size, growing larger with increased joint activity and shrinking with rest.
Treatment and Recurrence
A significant number of ganglion cysts resolve on their own without any treatment. If a cyst isn’t painful or interfering with function, watching and waiting is a reasonable approach.
When treatment is needed, the two main options are aspiration (draining the fluid with a needle) and surgical removal. Aspiration is quick and can be done in a doctor’s office, but the recurrence rate is high, between 60% and 95%, because the cyst wall and the capsular defect that caused it remain intact. The fluid simply refills over time.
Surgical excision removes both the cyst and a portion of the joint capsule or tendon sheath it’s attached to. Recurrence rates after surgery range from 1% to 50%, a wide range that depends on the cyst’s location, size, and how thoroughly the root was removed. Surgery carries its own risks, including stiffness, scarring, and nerve irritation, so it’s generally reserved for cysts that keep coming back or that cause persistent pain.
One approach that doesn’t work: smashing the cyst with a heavy object, the old “Bible bump” remedy. This can damage surrounding structures and doesn’t address the underlying defect, so the cyst almost always returns.