What are the common reasons for inflamed tonsils?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Inflamed tonsils are most commonly caused by infections, which may be either bacterial (such as strep throat) or viral (such as the flu, mononucleosis, or the common cold). In some cases, tonsils may become enlarged on just one side, which can indicate a localized infection, an abscess, a cyst, or, less commonly, a growth that requires medical evaluation.

Because the causes of tonsil inflammation range from mild viral infections to conditions that need prompt treatment, identifying the underlying issue matters. A free, instant, online symptom check can help you quickly narrow down possible causes based on your specific symptoms and guide you on the best next steps—whether that means home care, seeing a doctor, or seeking urgent evaluation.

Reviewed for medical accuracy: 07/20/2026

Important Next Steps

Discover what's causing inflamed tonsils Learn if your tonsils need care Find out if inflamed tonsils are serious See OTC relief for inflamed tonsils Find a doctor for tonsil problems Discover home remedies for inflamed tonsils Understand if throat symptoms need a check

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Explanation

Inflamed tonsils, also known as tonsillitis, are usually caused by infections. These infections can be due to viruses or bacteria. Common causes include:

Viral Infections: These are the most frequent causes of inflamed tonsils, such as the common cold or flu.
Bacterial Infections: Streptococcus bacteria, which cause strep throat, are a well-known cause of bacterial tonsillitis. However, non-streptococcal bacteria can also cause tonsillitis and may be treated with antibiotics like metronidazole.

Sometimes, only one tonsil may become enlarged, which could indicate a different underlying issue. If you're experiencing symptoms of tonsillitis or want to better understand what might be causing your throat discomfort, try our free AI-powered symptom checker to get personalized insights in minutes. In rare cases, severe tonsillitis can lead to complications, such as sudden death in children, though this is uncommon. Understanding these causes can help in managing and treating inflamed tonsils effectively.

(References)

Cortez EA, Mattox DE, Holt GR, & Gates GA. (1979). Unilateral tonsillar enlargement. Otolaryngology and head and neck surgery, 530694.
Byard RW. (2008). Tonsillitis and sudden childhood death. Journal of forensic and legal medicine, 18926504.
Brook I, & Gober AE. (2005). Treatment of non-streptococcal tonsillitis with metronidazole. International journal of pediatric otorhinolaryngology, 15627449.

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