Tonsillitis is inflammation of the tonsils most commonly caused by viral or bacterial infection. Symptoms may include sore throat and fever.

At the back of your throat, two masses of tissue called tonsils act as filters, trapping germs that could otherwise enter your airways and cause infection. They also produce antibodies to fight infection. But sometimes the tonsils themselves become infected. Overwhelmed by bacteria or viruses, they swell and become inflamed, a condition known as tonsillitis.