causes of swollen thumb
1 Insect bites and stings can also cause thumb swelling. Local inflammation, itching, burning and swelling can result after an insect bite, it may persist for few hours before healing on its own.  Infection of the thumb can also cause its swelling. It can be a secondary infection due to trauma and cut on the thumb.
Trauma and injury to the thumb, hand and wrist, is the most common cause for thumb swelling. Injury while playing or occupational injury to the thumb may cause swelling of thumb. Sometime an injury may cause fracture of the thumb bone. In such cases, X-ray of the thumb may be necessary to detect the fracture.
1 Arthritis and osteoarthritis of small joints may affect the thumb joint. It may lead to thumb swelling, pain and restricted thumb movement. Together with thumb, other fingers may also get affected with Arthritis.  Thumb tendonitis and bursitis can also cause inflammation and pain in the thumb.