Tonsillitis is typically caused by viral or bacterial infections. Common viruses include adenoviruses, influenza, and Epstein-Barr virus, while bacterial tonsillitis is often due to Streptococcus pyogenes, the bacteria responsible for strep throat. Tonsillitis can spread through respiratory droplets from coughing or sneezing, as well as through shared utensils or close contact with an infected person. Maintaining good hygiene practices can help reduce the risk of contracting tonsillitis.