Thumb swelling is caused by many different factors. It may be caused by a preexisting disorder, such as arthritis, tendonitis, or bursitis. Swelling of the thumb can also be caused by injury from trauma, repeated use, or an insect or animal bite. Most thumb injuries are mild and heal on their own, but if symptoms are severe a doctor may be needed to treat the swelling.

Arthritis is one of the most common causes of thumb swelling. Osteoarthritis can occur in the thumb for a variety of reasons, ranging from normal wear and tear to overuse of the basal joint. The basal joint is the joint just above the wrist that is responsible for thumb movement. Symptoms range from mild to severe, including swelling, stiffness, and pain.

Thumb tendonitis is another cause of thumb swelling. It is caused when the tendons at the base of the thumb become irritated, typically from repeated, uncomfortable movement of the hands and wrists. One of the most common causes of thumb tendonitis is all of the difficult and unusual hand positions that are required for a new mother to take care of her infant.

Burstitis is a similar, somewhat less common, cause of thumb swelling. It is the inflammation of the fluid-filled sac located between the bones and tendons or muscles around them. This sac forms a sort of cushion against the hard surface of the bone. Bursitis can be one of the most painful causes of a swollen thumb.

Trauma injuries to the hand or wrist may also cause thumb swelling. Fractures in the bones of the thumb can cause swelling. X-rays will be necessary to detect any bone fractures. Difficulty moving the thumb may indicate a fracture is present. A joint sprain is another fairly common injury that can cause a swollen thumb.

Bowling is another common cause of thumb swelling. This swelling occurs due to repeated use, placing the thumb into the holes of the bowling ball. The stress to the fingers when the ball leaves the hand can cause some swelling and even a little soreness. This is generally nothing to worry about, as bowling rarely causes injury. Do see a doctor, however, if the pain is severe.

Any repeated activity involving the thumb can cause thumb swelling. Text messaging is one example of an activity that can cause swelling and even pain due to overuse. Playing an instrument that uses the thumbs a lot can have the same effect.

Animal or insect bites are also common causes of thumb swelling. Just like any other part of the skin, if an insect or animal bites the skin on the thumb, it may result in swelling. Other common symptoms of these bites are itching, redness, and sometimes pain. The swelling indicates that the body is reacting to venom, or it could also be caused by inflammation due to tissue damage.