No one knows exactly what causes a ganglion cyst to develop. It grows out of a joint or the lining of a tendon, looking like a tiny water balloon on a stalk, and seems to occur when the tissue that surrounds a joint or a tendon bulges out of place. Inside the cyst is a thick lubricating fluid similar to that found in joints or around tendons.
Factors that may increase your risk of ganglion cysts include:
Your sex and age. Ganglion cysts can develop in anyone, but they most commonly occur in women between the ages of 20 and 40.
Osteoarthritis. People who have wear-and-tear arthritis in the finger joints closest to their fingernails are at higher risk of developing ganglion cysts near those joints.
Joint or tendon injury. Joints or tendons that have been injured in the past are more likely to develop ganglion cysts.