Tonsillitis is an inflammation of the tonsils, which are lymph glands located on both sides of the throat that help fight infections. It is commonly caused by bacterial or viral infections and symptoms include sore throat and painful swallowing. Diagnosis involves a throat swab and blood tests. Treatment consists of pain relievers, antibiotics if bacteria are detected, and tonsillectomy for recurring cases. Complications can include spread of infection or abscesses.