Swollen tonsils are most often caused by a viral infection. Viruses account for 70% to 95% of all tonsillitis cases, making them far more common than bacterial causes. The swelling is your immune system’s response to an invader: your tonsils sit at the back of your throat like sentries, trapping germs and ramping up inflammation to fight them off. That fight is what makes them puff up, turn red, and hurt.
Viral Infections: The Most Common Cause
The usual suspects behind swollen tonsils are the same viruses that cause colds and upper respiratory infections: rhinovirus, adenovirus, respiratory syncytial virus, and coronavirus. These infections typically bring a sore throat, mild fever, runny nose, and general fatigue. The swelling usually peaks within a few days and resolves on its own within one to two weeks without antibiotics.
One less common but notable viral cause is Epstein-Barr virus, which causes mononucleosis (mono). Mono deserves special attention because it hits harder and lasts longer. You’ll typically feel extreme fatigue along with a sore throat, swollen tonsils (sometimes coated with a white film), and enlarged lymph nodes in the neck. The fever and sore throat usually ease within a couple of weeks, but the fatigue and swollen lymph nodes can linger for weeks beyond that. Mono is most common in teenagers and young adults, and it spreads through saliva.
Strep Throat and Bacterial Causes
Bacteria cause only a small fraction of tonsil infections, but they matter because they require antibiotics. Group A streptococcus (the germ behind strep throat) is responsible for 5% to 15% of adult tonsillitis cases and 15% to 30% of cases in children aged 5 to 15. Strep tends to come on suddenly with a high fever, intensely painful swallowing, and swollen tonsils that may have white or yellow patches. Notably, strep usually does not come with a cough, runny nose, or hoarseness. If you have those cold-like symptoms, a virus is far more likely.
Doctors use a simple checklist to estimate the likelihood of strep: swollen tonsils with white patches, tender lymph nodes in the front of the neck, fever over 100.4°F, and no cough. The more of these signs you have, the higher the probability. With all four present, the chance of strep is roughly 50/50, which is why a rapid strep test or throat culture is still needed to confirm it. If strep is confirmed, the standard treatment is a 10-day course of penicillin or amoxicillin.
Non-Infectious Causes
Not every case of swollen tonsils involves an active infection. Postnasal drip from allergies or chronic sinus issues can irritate and inflame tonsil tissue over time. When mucus constantly drains down the back of your throat, it creates a low-grade irritation that keeps the tonsils swollen even without a fever or other signs of infection. If your swollen tonsils come with itchy eyes, sneezing, or seasonal patterns, allergies may be the underlying driver.
Tonsil stones are another non-infectious cause. These are small, hard lumps made of trapped food particles, dead cells, bacteria, and calcium that form in the tiny pockets on the surface of your tonsils. They look like white or yellow pebbles and can cause localized swelling, bad breath, and a persistent feeling of something stuck in your throat. They’re not dangerous, but they can be annoying. Many people dislodge them on their own with gentle pressure or gargling.
When One Side Is More Swollen Than the Other
If only one tonsil is significantly larger than the other, pay attention. Bilateral swelling (both sides) is typical of infections. Unilateral swelling can still be infectious, but it raises a different set of concerns.
The most urgent possibility is a peritonsillar abscess, a pocket of pus that forms next to a tonsil, usually as a complication of untreated tonsillitis. Warning signs include severe throat pain concentrated on one side, difficulty opening your mouth, a muffled or “hot potato” voice, and a visible shift of the uvula (the dangling tissue in the back of your throat) away from the swollen side. If the swelling becomes severe enough to make breathing difficult, that’s an emergency.
Persistent, painless enlargement of a single tonsil, particularly in adults, can in rare cases signal a more serious condition like lymphoma or other cancers of the head and neck. This is uncommon, but a tonsil that stays enlarged for weeks without other infection symptoms warrants a medical evaluation.
Managing Swollen Tonsils at Home
Since most tonsil swelling is viral, the primary approach is comfort care while your immune system does its job. Saltwater gargles are a simple and effective way to reduce swelling and ease pain. Mix about 1/4 to 1/2 teaspoon of salt into 8 ounces of warm water and gargle for 15 to 30 seconds. You can repeat this several times a day.
Cold liquids, ice pops, and soft foods help when swallowing is painful. Over-the-counter pain relievers reduce both pain and inflammation. Staying well hydrated matters more than people realize, because a sore throat often leads to drinking less, which can slow recovery. Warm broth and herbal tea are easier to get down than room-temperature water for many people.
If your symptoms point to strep (sudden onset, high fever, no cough, white patches on the tonsils), get tested rather than waiting it out. Untreated strep can lead to complications, and antibiotics shorten the duration and reduce the chance of spreading it to others.
When Tonsillitis Keeps Coming Back
Some people deal with tonsillitis multiple times a year, and at a certain point, surgery becomes a reasonable option. Clinical guidelines recommend considering tonsillectomy if you’ve had at least 7 episodes in one year, at least 5 episodes per year for two consecutive years, or at least 3 episodes per year for three consecutive years. Each episode needs to be documented with at least one objective sign: fever over 101°F, swollen neck lymph nodes, tonsillar exudate, or a positive strep test.
Tonsillectomy is more commonly performed in children, but adults who meet these thresholds can benefit as well. Recovery typically takes one to two weeks and involves significant throat pain, so it’s not a decision made lightly. For people who qualify, though, it can mean a dramatic drop in the number of throat infections going forward.