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Canker sores, also called aphthous ulcers, are small, oval sores that form in the soft tissues of your mouth. A canker sore can develop on the inside of your cheek, under your tongue, on the insides of your lips.

They can also develop in the back of the throat or on the tonsils.

These painful sores usually have a distinct red edge with a white, gray, or yellowish center. Unlike cold sores, which are caused by the herpes simplex virus, canker sores are not contagious.

A canker sore on your tonsil can be very painful, causing a sore throat on one side. Some people even mistake it for strep throat or tonsillitis.

Depending where exactly the sore is, you may be able to see it if you look into the back of your throat. It will usually look like a small, single sore.

You may also feel tingling or burning in the area a day or two before the sore develops. Once the sore forms, you might also feel a stinging sensation when you eat or drink something acidic.

No one’s sure about the exact cause of canker sores.

But certain things seem to trigger them in some people or increase their risk of developing them, including:

Some medical conditions may also trigger canker sores, including:

Though anyone can develop a canker sore, they’re more common in teens and young adults. They’re also more common in females than males. Family history also appears to play a role in why some people get recurring canker sores.

Most canker sores heal on their own without treatment in about a week.

But occasionally people with canker sores develop a more severe form called major aphthous stomatitis.

These sores often:

  • last two or more weeks
  • are bigger than typical canker sores
  • cause scarring

While neither type requires treatment, over-the-counter (OTC) products may help to relieve pain during the healing process, including:

  • mouth rinses containing menthol or hydrogen peroxide
  • topical mouth sprays containing benzocaine or phenol
  • nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen

The tonsils can be hard to reach, so a mouth rinse may be the easiest option. As you recover, try to limit spicy or acidic foods, which can irritate the canker sore.

If you have a very large canker sore, or multiple small canker sores, consider seeing your healthcare provider. They may prescribe a steroid mouthwash to speed up healing.

Many OTC mouth sprays are not intended for use in children. Consult your child’s healthcare provider for safe treatment alternatives.

If you’re looking for easy relief from a canker sore, several home remedies may also help, such as:

  • making a baking soda or saltwater rinse made with a 1/2 cup warm water and one teaspoon of salt or baking soda
  • applying milk of magnesia on the sore several times a day using a clean cotton swab
  • gargling with cold water to help relieve pain and inflammation

The tonsils aren’t a common site for canker sores — but it can certainly happen. You’ll likely experience some throat pain for a few days, but the sore should heal on its own within a week or two.

If you have a very large canker sore or sores that don’t seem to be getting better, make an appointment with your healthcare provider.