Carpal tunnel syndrome is swelling in the compartment in the wrist that contains wrist and finger muscles, nerves, and blood supply. It can be caused by bending your wrist repeatedly over a large amount of time due to things such as working with a typewriter or hammering nails. It can be caused by swelling in the wrist joint caused by a trauma such as falling on the hand. Arthritis can cause the swelling associated with carpal tunnel syndrome, and sometimes swelling from pregnancy can give you carpal tunnel syndrome symptoms.

The swelling puts pressure on the nerve that travels in this compartment or "tunnel". This nerve is called the median nerve. Pressure on the median nerve causes numbness, weakness, and pain in the wrist and hand.