Tonsillitis is caused by bacterial pharyngitis or viral pharyngitis.

Causes of bacterial pharyngitis, which may result in tonsillitis, include:

• Arcanobacterium haemolyticum
• Beta-hemolytic streptococci:
• The cause of strep throat
• Chlamydia pharyngitis
• Mycoplasma pharyngitis

Causes of viral pharyngitis, which may result in tonsillitis, include:

• Adenovirus
• Epstein-Barr virus
• Influenza virus
• Parainfluenza virus
• Enterovirus
• Mononucleosis