Most tonsillitis is viral, and the single strongest clue that yours might be bacterial instead is the absence of a cough. Viruses tend to cause a constellation of cold-like symptoms alongside the sore throat, while bacterial infections, particularly group A strep, zero in on the throat itself. You can’t diagnose the cause at home with certainty, but several reliable patterns can help you gauge what you’re dealing with before you see a doctor or decide whether you need to.
Viral Tonsillitis: What It Looks Like
Viral tonsillitis behaves like an extension of a cold or flu. Along with swollen, red tonsils and a sore throat, you’ll typically notice a cough, runny nose, congestion, or red, watery eyes. These “whole body” symptoms are the hallmark of a virus. The sore throat is real, but it arrives in the company of other upper respiratory complaints rather than standing alone.
Some viral causes produce distinctive mouth findings. Coxsackievirus infections (sometimes called herpangina) create small, grayish-white blisters on the soft palate that quickly become shallow ulcers with a red rim. Herpes simplex can cause ulcerative sores on the back of the throat or tonsils that look surprisingly similar to strep. Epstein-Barr virus, the cause of mono, often mimics strep so convincingly that the two are frequently confused. One telling sign of mono: a sore throat that doesn’t improve after a course of antibiotics.
Viral tonsillitis generally resolves on its own within 7 to 10 days. There’s no antibiotic that speeds it along, so treatment focuses on managing pain and staying hydrated.
Bacterial Tonsillitis: What It Looks Like
Group A streptococcus is the most common bacterial culprit, responsible for 20% to 30% of sore throat episodes in children and 5% to 15% in adults. That means even in kids, the majority of tonsillitis cases are still viral. But when strep is the cause, the pattern shifts.
Bacterial tonsillitis tends to come on fast. The tonsils often have white or yellow patches of pus (exudates), and the lymph nodes under the front of the jaw feel swollen and tender. Fever is common, usually 38°C (100.4°F) or higher. The critical negative finding is what’s missing: no cough, no runny nose, no congestion. If your throat is on fire but you’re not sniffling or coughing, that tilts the odds toward bacteria. You may also notice tiny red spots (petechiae) on the roof of your mouth, which can appear with strep-related scarlet fever.
The Centor Score: A Quick Self-Check
Doctors use a simple four-point checklist called the Centor score to estimate how likely a sore throat is to be strep. You can run through it yourself:
- Fever of 38°C (100.4°F) or higher: 1 point
- White or yellow patches on the tonsils: 1 point
- Swollen, tender lymph nodes at the front of the neck: 1 point
- No cough: 1 point
A score of 0 to 2 makes strep unlikely. In one study, no patients scoring in that range tested positive. A score of 3 carries roughly a 37% chance of strep. A score of 4 makes it highly probable. This isn’t a diagnosis, but it’s the same framework your doctor uses to decide whether testing is worthwhile.
How Doctors Confirm the Cause
The only way to confirm bacterial tonsillitis is a lab test. The most common is a rapid antigen detection test, often called a rapid strep test. A swab of the back of the throat gives results in minutes. These tests are good at ruling strep in: they correctly identify people who don’t have it about 95% of the time. But they miss roughly 14% of true strep cases, meaning a negative result isn’t perfectly reliable.
Because of that gap, doctors sometimes follow a negative rapid test with a throat culture, especially in children. A culture takes 24 to 48 hours but catches cases the rapid test misses. In adults, where strep is less common and complications are rarer, a backup culture is less routine.
If mono is suspected, a separate blood test checks for Epstein-Barr virus antibodies. This is worth pursuing when the sore throat is severe, fatigue is overwhelming, and the rapid strep test comes back negative.
Why It Matters to Get It Right
Viral tonsillitis is self-limiting. It’s miserable, but it resolves without specific treatment. Bacterial tonsillitis from group A strep carries real risks if left untreated. The most serious is rheumatic fever, a condition that can inflame the heart, joints, brain, and skin. Rheumatic fever can lead to rheumatic heart disease, which weakens the heart valves and in severe cases requires surgery. These complications are preventable with a standard course of antibiotics, typically penicillin taken for 10 days.
On the flip side, taking antibiotics for a viral infection doesn’t help and contributes to antibiotic resistance. Getting tested when your symptoms point toward bacteria, and skipping antibiotics when they don’t, is the balance doctors aim for.
Symptoms That Need Immediate Attention
Regardless of whether the cause is viral or bacterial, certain symptoms signal something more serious. Increasing pain with swallowing, especially if you’re having trouble swallowing your own saliva or drooling, can indicate a peritonsillar abscess or dangerous swelling. Neck swelling that’s getting worse, shortness of breath, or a whistling sound when you breathe are reasons to seek emergency care right away. These complications are uncommon but can escalate quickly.