What are the common causes of swollen tonsils in adults?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Swollen tonsils in adults are most often caused by infections, including viral or bacterial tonsillitis (such as strep throat), chronic tonsillitis, and mononucleosis. Other causes include unilateral tonsillar enlargement, tonsil stones, allergies, acid reflux, and, in rare cases, tumors. Symptoms may include sore throat, difficulty swallowing, fever, and visible redness or white patches.

Because swollen tonsils can point to a wide range of conditions—from mild irritation to more serious infections—it's important to identify the cause early. A free, instant, online symptom check can help you understand what may be behind your symptoms and guide you toward the right next steps, whether that's home care or seeing a doctor.

Reviewed for medical accuracy: 07/20/2026

Important Next Steps

Learn what may be causing swollen tonsils See if swollen tonsils need urgent care Discover if your swollen tonsils signal infection Find OTC relief for swollen tonsil pain Find a doctor for tonsil-related symptoms Explore home remedies for swollen tonsils Check if swollen tonsils need treatment

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Explanation

Swollen tonsils, or tonsillitis, can happen when the tonsils enlarge and get sore. In adults, this can be due to infections.

Common Causes:

Chronic Tonsillitis: This is when your tonsils stay swollen and sore for a long time. It can happen because of bacteria and other tiny germs. Sometimes, these germs form a sticky group called a biofilm, which makes it hard to treat.
Unilateral Tonsillar Enlargement: This means one tonsil is bigger than the other. It can happen because of infections or other issues in the throat.

What to Do:

If your tonsils are swollen, you can use Ubie's free AI symptom checker to help identify what might be causing your symptoms and determine if you need to see a healthcare provider.

(References)

Pribuišienė R, Kuzminienė A, Sarauskas V, Saferis V, Pribuišis K, & Rastenienė I. (2013). The most important throat-related symptoms suggestive of .... Medicina (Kaunas, Lithuania), 24247917.
Cortez EA, Mattox DE, Holt GR, & Gates GA. (1979). Unilateral tonsillar enlargement. Otolaryngology and head and neck surgery, 530694.
Abu Bakar M, McKimm J, Haque SZ, Majumder MAA, & Haque M. (2018). Chronic tonsillitis and biofilms: a brief overview of treatment .... Journal of inflammation research, 30233227.

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