What are the potential causes of unilateral tonsil swelling?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Unilateral tonsil swelling—when one tonsil is noticeably larger than the other—can result from several underlying causes, including bacterial or viral infections (such as tonsillitis, strep throat, or mononucleosis), peritonsillar abscess, tonsil stones, or, in less common cases, tumors or lymphoma. Because the causes range from mild to serious, identifying the reason early is key to getting the right treatment.

If you're noticing one swollen tonsil and want quick clarity on what might be causing it, taking a free, instant, online symptom check is a smart first step. It only takes a few minutes, requires no sign-up, and helps you understand possible conditions linked to your symptoms—so you can make informed decisions about whether to see a doctor and how urgently.

Reviewed for medical accuracy: 07/20/2026

Important Next Steps

Learn causes of unilateral tonsil swelling Discover if tonsil swelling needs urgent care Find out what’s causing your swollen tonsil See OTC options for tonsil swelling pain Find a doctor for tonsil conditions Understand home remedies for swollen tonsils Check if one swollen tonsil is serious

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Explanation

Unilateral tonsil swelling means that one tonsil is bigger than the other. This can happen for a few reasons.

Possible Causes:

Infections: Sometimes, infections like a sore throat or an abscess can make one tonsil swell.
Tumors: In some cases, a growth or tumor could be the reason. This includes both non-cancerous and cancerous types, like lymphoma.
Other Conditions: Other medical issues might also cause one tonsil to enlarge, such as certain immune system problems.

Importance of Medical Evaluation:

It's important to visit a doctor if one tonsil is swollen. To help identify your symptoms and understand potential causes before your appointment, you can use Ubie's free AI symptom checker. Remember, only a healthcare professional can provide a proper diagnosis and treatment plan.

(References)

Cortez EA, Mattox DE, Holt GR, & Gates GA. (1979). Unilateral tonsillar enlargement. Otolaryngology and head and neck surgery, 530694.
Guimarães AC, de Carvalho GM, Correa CR, & Gusmão RJ. (2015). Association between unilateral tonsillar enlargement and .... Critical reviews in oncology/hematology, 25487766.
Berkowitz RG, & Mahadevan M. (1999). Unilateral tonsillar enlargement and tonsillar lymphoma in .... The Annals of otology, rhinology, and laryngology, 10527279.

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