What Causes Tonsillitis and Why Some People Are More Likely to Get It

Tonsils are an important part of your immune system and the first line of defense against viruses or bacteria that you inhale or swallow.

They are lumps of a type of tissue called lymphoid tissue in the back of your mouth (flanking the uvula, which hangs down centered above the throat).

Technically, you have a few different types of tonsils, including two palatine tonsils — the large ones you generally think of as your tonsils — a clump of nasopharyngeal tonsils (known as adenoids), two tubal tonsils, and a clump of lingual tonsils.

When it comes to tonsillitis, doctors usually refer to the large palatine tonsils as your tonsils and your adenoids, which are located in the back of the throat above the uvula rather than on the sides of the back of the throat where the other tonsils sit.

Tonsillitis refers to when the tonsils (and sometimes the adenoids, too) become inflamed or infected.

Tonsils work to trap the germs that come in through the mouth and nose. Although it’s the tonsils’ job to fight off these attackers, they are also vulnerable to infection. Most of the time tonsillitis is caused by a viral infection, such as a cold, although bacterial infections such as strep throat can also be the culprit.

Tonsillitis can be caused by any of the following:

Viruses (most common)
Bacteria, such as Streptococcus pyogenes (that’s group A streptococcus, more commonly referred to as strep)
Fungal infections
Parasitic infections
Cigarette smoke
Other causes

Tonsils are the first port of call for viruses and bacteria, Dr. Clark says — and that makes them particularly vulnerable to infection. Although the actual tonsillitis infection is not contagious, the viruses and bacteria that cause it are.

It seems simple enough: Viral infections are caused by a virus, and bacterial infections are caused by bacteria. The hard part can be telling the difference, even for doctors. Infections caused by either can present in the same way, with fever, pain, and irritability, Clark explains.

Your doctor may be able to make a clinical tonsillitis diagnosis to distinguish which kind of tonsillitis you have, which would be based on the description of your symptoms, the timing and severity of your symptoms, and your medical history. There are also diagnostic tests that a doctor may order to determine the origin of the infection.

If it’s a viral infection, an antibiotic won’t help speed recovery, as antibiotics are only effective for bacterial infections. Sometimes a viral infection can cause a secondary infection that is bacterial.

For example, a bacterial ear infection can sometimes result from viral tonsillitis.

Tonsillitis is usually painful, especially while swallowing. How bad it feels can vary, as everyone experiences pain differently, Clark says. Along with a sore throat, there can be the accompanying aches that go along with a fever, as well as enlarged and tender glands, or lymph nodes, in the neck. Headache, a stiff neck, and even a stomachache (particularly in children) can be part of tonsillitis, Clark says.

Although it is more common for children to be diagnosed with tonsillitis, adults can get it, too, Clark says. “As we age, the tonsils atrophy and become less active in the immune system,” he explains. “This shrinkage may account for tonsillitis being less common in adults compared to children.”

Another reason that tonsillitis is more likely to occur with children than with adults is that children are more likely to have viral infections, says Nicholas Rowan, MD, associate professor of otolaryngology at John Hopkins Medicine in Baltimore. “Just like a child is more likely to have a common cold or a sore throat, they are more likely to have tonsillitis. That’s the reason for the higher incidence,” says Dr. Rowan.

But everyone should take precautions against tonsillitis because anyone can catch it.

The germs that cause the viral and bacterial infections that cause tonsillitis are contagious. Practicing good hygiene is the best defense against catching these infections (and therefore avoiding tonsillitis), Clark says. These practices include the following:

Wash your hands frequently.
Practice good oral care.
Avoid sharing food, drinking glasses, water bottles, or utensils.
Replace toothbrushes after having an infection.
Stay at home if you have an infection.
Support a healthy oral microbiome with a diet rich in fruits and vegetables.

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