Tonsillitis is inflammation of the tonsils most commonly caused by a viral or bacterial infection. Symptoms of tonsillitis include sore throat and fever. While no treatment has been found to shorten the duration of viral tonsillitis, bacterial causes such as streptococcal pharyngitis are treatable with antibiotics. It usually takes one to three weeks to recover.

Common symptoms of tonsillitis include:

In cases of acute tonsillitis, the surface of the tonsil may be bright red and with visible white areas or streaks of pus.

Tonsilloliths occur in up to 10% of the population frequently due to episodes of tonsillitis.

The most common causes of tonsillitis are adenovirus, rhinovirus, influenza, coronavirus, and respiratory syncytial virus. It can also be caused by Epstein-Barr virus, herpes simplex virus, cytomegalovirus, or HIV. The second most common causes are bacterial. The most common bacterial cause is Group A β-hemolytic streptococcus (GABHS), which causes strep throat. Less common bacterial causes include: Staphylococcus aureus ( including methicillin resistant Staphylococcus aureus or MRSA ),Streptococcus pneumoniae, Mycoplasma pneumoniae, Chlamydia pneumoniae, pertussis, Fusobacterium, diphtheria, syphilis, and gonorrhea. A concomitant GABHS and influenza A virus pharyngotonsillitis can occur, as was evident by an increased in the ASO and anti-DNase B titers in a third of the patients who had both of these organisms isolated.