Tonsils are composed of soft glandular tissue and are the body's primary point of defence in the immune system. The primary function of tonsils is to trap bacteria and viruses that enter the human body through breathing and eliminating them. They help in the prevention of throat and drug infections. The white spots that appear on the tonsils are caused by pus that appears on the surface of the tonsils. This pus appears when an infection of the tonsils known as tonsillitis occurs. The symptoms of tonsillitis include fever, headache, sore throat, cough, swelling of the neck, painful swallowing etc. The condition lasts for around a week's time before healing. It is sometimes possible that these white spots may be ca sign of strep throat and if they persist beyond a week a physician should be consulted.