The thumb could be swollen due to arthritis-rheumatoid, gout, injury (like thumb twisted while sleeping
), inflammation of the sac of joint, a *****, insect bite, allergy or contact dermatitis to something, tendon injury or inflammation, clot in blood vessel, infection of the skin or pulp of the thumb etc.
Dip your entire thumb in warm water to which a pinch of salt is added. Keep it in for 5-10 minutes. Do this 3-4 times in a day. Take an OTC analgesic and anti-inflammatory pill.