A swollen tonsil is usually a sign that your body is fighting off an infection, most often viral. Tonsils are part of your immune system, and they swell when they trap and respond to bacteria or viruses entering through your mouth and nose. In most cases, the swelling resolves on its own within a week or two. But the specific cause matters, especially if only one tonsil is swollen, because that pattern can point to conditions that need different treatment.
Viral vs. Bacterial Tonsillitis
The most common reason for swollen tonsils is tonsillitis, an infection of the tonsil tissue itself. Both viruses and bacteria can cause it, and telling them apart matters because only bacterial tonsillitis responds to antibiotics.
Viral tonsillitis tends to produce milder symptoms. You might have a sore throat, low-grade fever, runny nose, and a cough. Bacterial tonsillitis, usually caused by group A streptococcus (strep throat), generally hits harder: higher fever, white or yellow patches on the tonsils, swollen lymph nodes along the neck, and notably no cough. That last detail is one of the key clinical clues. Doctors often use a quick swab of the back of your throat to test for strep. If it comes back positive, you have a bacterial infection. If negative, a virus is the likely culprit, and treatment focuses on managing symptoms while your body clears it.
Mono and Longer-Lasting Swelling
If your tonsils have been swollen for more than a week and you’re dealing with extreme fatigue, infectious mononucleosis (mono) could be responsible. Caused by the Epstein-Barr virus, mono is especially common in teenagers and young adults. About half of people with mono develop a white coating or patches on their tonsils, and the swelling can be significant enough to make swallowing painful.
Mono symptoms typically last anywhere from three days to eight weeks, which is considerably longer than a standard sore throat. There’s no antibiotic for it since it’s viral. Recovery is mostly about rest, fluids, and time. Your doctor may test for it with a blood test if strep comes back negative and your symptoms persist.
Why Only One Tonsil May Be Swollen
Swelling on just one side deserves closer attention. Several conditions can cause this, and they range from easily treatable to serious.
Peritonsillar Abscess
A peritonsillar abscess (sometimes called quinsy) happens when pus collects in the tissue next to the tonsil, usually as a complication of untreated or poorly treated tonsillitis. It typically causes a severe sore throat on one side, difficulty swallowing, fever, and a muffled “hot potato” voice, as if you’re speaking with something stuck in your mouth. One of the hallmark signs is trismus: difficulty opening your mouth because the surrounding muscles are inflamed and in spasm. On examination, the soft palate on the affected side bulges, and the uvula gets pushed toward the opposite side.
This is not something to manage at home. If left untreated, a peritonsillar abscess can obstruct your airway, rupture and cause you to aspirate pus, or spread infection deeper into the neck where it can threaten nerves and blood vessels. If you have a one-sided sore throat with difficulty opening your mouth, a muffled voice, or trouble swallowing fluids, seek medical care promptly.
Tonsil Stones
A less alarming cause of one-sided swelling is tonsil stones. These are small, hard deposits that form in the crevices of your tonsils from trapped food particles, bacteria, and dead cells. Small ones often cause no symptoms at all. Larger stones can produce persistent bad breath, a feeling of something stuck in your throat, a sore throat, earache, or difficulty swallowing. You might spot them as white or yellow lumps on the tonsil surface.
Keeping up with oral hygiene helps prevent them. Brushing the back of your tongue, gargling with salt water, using an antimicrobial mouthwash, and staying hydrated can all reduce buildup. Most tonsil stones dislodge on their own. Surgery to remove the tonsils is rarely needed and is generally reserved for stones that grow large or keep coming back despite self-care.
Postnasal Drip and Chronic Irritation
Allergies, sinus problems, and environmental irritants can cause a steady stream of mucus to drip down the back of your throat. This postnasal drip irritates the tissue, and your tonsils can swell in response. The swelling in this case tends to be less dramatic than with an infection. You won’t have a fever or white patches. Instead, you’ll notice a persistent scratchy throat, frequent throat clearing, and possibly a mild cough, especially at night. Treating the underlying allergy or sinus issue usually brings the tonsil swelling down over time.
What You Can Do at Home
For mild swelling from a viral infection, home care is the main treatment. Drinking plenty of fluids, eating soft foods, and using over-the-counter pain relievers for fever and throat pain are the basics. Gargling with warm salt water may soothe throat discomfort for some people, though it won’t shorten the duration of the illness. Cold foods like ice pops or smoothies can also help numb the pain temporarily.
Rest matters more than most people expect. Your immune system does its heaviest work while you sleep, and pushing through a viral illness often just extends it.
Red Flags Worth Knowing
Most swollen tonsils resolve without complications. But certain signs suggest something more serious is going on and should prompt a medical visit:
- Difficulty breathing or swallowing fluids. This can indicate significant airway narrowing, especially if both tonsils are enlarged enough to nearly touch (“kissing tonsils”).
- Inability to open your mouth fully. Trismus points toward an abscess forming near the tonsil.
- A muffled or changed voice. The “hot potato” voice is a classic sign of a peritonsillar abscess.
- One tonsil growing rapidly with no pain. Painless, fast-growing enlargement on one side, particularly with swollen neck lymph nodes, unexplained weight loss, night sweats, or persistent fevers, raises concern for lymphoma. About 73% of tonsil lymphoma cases in younger patients present as one-sided enlargement.
- Visible changes to the tonsil surface. Ulceration, color changes, or an unusual-looking lesion on the tonsil that doesn’t fit a typical infection warrants evaluation.
Swollen tonsils are overwhelmingly caused by common infections that resolve in days to weeks. But paying attention to whether one or both sides are affected, how long the swelling lasts, and whether you have any of the warning signs above helps you know when it’s safe to ride it out and when it’s time to get checked.