Canker sores: what causes them, and how should you maintain oral hygiene while you have them?

Canker sores are small, painful ulcers in the oral mucosa that almost everyone experiences sooner or later. They appear suddenly and can make eating and speaking difficult; despite their small size, they can be very bothersome. In this article, we explain what canker sores are, what causes them, and where they most often appear: on the tongue, gums, or near a tooth. We also explain how to maintain oral hygiene while a sore is still painful without irritating it further, and when it should be checked by a doctor or dentist.

What are canker sores, and why do they develop?

A canker sore is a small, round or oval erosion of the oral mucosa, usually whitish or yellowish in color and surrounded by a red border. Canker sores are usually a few millimeters in size, though larger ones can also occur. They are characteristically painful, with pain that worsens when eating or drinking, and even when speaking or brushing your teeth. Canker sores are among the most common harmless changes in the mouth. They appear alone or in small clusters and usually go away on their own within a few days to a couple of weeks. Although common, they still raise many questions because they can affect almost anyone, regardless of age.

What causes canker sores?

The causes of canker sores have not been clearly established, but several factors commonly associated with them have been identified.

Irritation and minor injuries in the mouth

Canker sores often appear after a minor mechanical injury: biting the cheek or tongue, being poked by the sharp edge of a chip or piece of toast, brushing too vigorously, or rubbing against braces. Local irritation of the oral mucosa can be the starting point for a sore to develop.

Stress, exhaustion, and other factors

Many people get canker sores during periods of increased stress, exhaustion, or weakened immunity. Certain foods, such as very acidic or spicy ones, and changes in daily routines may also play a role. These are factors that may contribute, rather than a single confirmed cause.

Why can canker sores recur?

Some people get canker sores repeatedly, every few weeks or months. This tendency to recur can vary from person to person and may be linked to the contributing factors mentioned above. If canker sores keep coming back and regularly make eating or speaking uncomfortable, it’s worth talking to a doctor or dentist rather than waiting for them to go away on their own each time.

Where do canker sores most often appear?

Canker sores can appear in different parts of the mouth, and their location affects how much they interfere with everyday activities.

Canker sores on the tongue

Canker sores on the tongue are among the most troublesome because the tongue is constantly moving when you eat, drink, speak and swallow. Even a small sore in this location can cause significant discomfort, and accidentally touching it with your teeth or toothbrush makes it hurt even more. That’s why it’s especially important to slow down when eating and brushing if you have a canker sore on your tongue.

Canker sore on the gum

Canker sores can also appear on the gums, both on the free gingiva and near the mucogingival junction. This location can easily become further irritated during brushing, especially if your toothbrush has stiff bristles or you brush too vigorously.

Canker sore on the gum near a tooth: what could it mean?

A canker sore in this location looks similar to one elsewhere: it’s a small, painful ulcer with a pale center and a red border. However, if a sore near a tooth looks unusual or is very painful, don’t wait - consult a dentist (a full list of situations requiring a consultation is below).

Canker sores on the inside of the cheeks and lips

The inside of the cheeks and lips are also common locations, as these areas are most prone to being bitten. The advice is the same as for other locations: avoid further irritation and be patient.

How long does a canker sore take to heal?

Healing time varies and depends mainly on the size of the canker sore and individual factors. Smaller sores usually heal faster than larger or more irritated ones.

Can a canker sore go away on its own?

Most canker sores heal on their own, without special treatment, within about one to two weeks. During this time, it’s important to avoid further irritating the sore: stay away from spicy, hard, very hot or strongly seasoned foods, and don’t touch it with your tongue or fingernail.

When should you consult a doctor about a canker sore?

If a canker sore lasts longer than usual, keeps coming back, looks unusual, or significantly interferes with eating and drinking, consult a doctor or dentist. Later in the article, we describe specific situations when you should make an appointment without delay.

What helps with canker sores in the mouth?

Since canker sores usually heal on their own, the question of “what to do about canker sores” mostly comes down to how to ease discomfort without interfering with the natural healing process.

How can you reduce irritation to a canker sore?

The key is to be gentle. When eating, avoid foods that could irritate the sore: very salty, acidic or spicy foods, or foods with sharp edges, such as chips, toast or nuts. It can also help to chew on the side of your mouth without a canker sore and drink lukewarm rather than hot beverages.

How should you maintain oral hygiene when you have a canker sore?

Oral hygiene remains important even when a canker sore hurts, because neglected plaque and food debris can themselves further irritate the lining of the mouth. The key is how you brush: gently, without pressing on the affected area, preferably with a soft brush head.

Oral hygiene when you have a canker sore

Getting a canker sore doesn't mean you need to stop brushing your teeth every day. However, it's important to avoid further irritating the sore spot and to be gentler than usual when taking care of your oral hygiene.

Can you brush your teeth when you have a canker sore?

Yes, brushing your teeth when you have a canker sore is recommended, as long as you do it carefully. Avoid direct contact with the sore, use gentle, short strokes, and don't press hard on the gums around it. Skipping toothbrushing just to avoid irritating the sore usually makes things worse, because it encourages plaque buildup.

Which toothbrush is suitable for a sensitive mouth?

For a sensitive mouth, a toothbrush that lets you choose the brushing intensity yourself can work well. The ZENT SoniQ sonic toothbrush has four modes, including Soft mode, designed for tissues prone to irritation and bleeding. So when you have a canker sore, you can switch to a gentler mode for a while instead of giving up thorough brushing. SoniQ combines sonic vibrations with oscillating movements of up to 40 degrees, and its built-in Smart Timer ensures a full two minutes of brushing and signals when to change areas every 30 seconds. A sonic toothbrush for gentle brushing is an everyday solution, not just for when a canker sore is healing.

Can you use a water flosser when you have canker sores?

It's worth being careful here. A water flosser isn't a treatment for canker sores and shouldn't be used as one. It's a device that supports daily cleaning between the teeth, including areas that dental floss and a toothbrush don't always reach effectively. If you have a canker sore, direct the water stream away from it and choose the gentlest pressure setting available to avoid further irritating the sore spot. The ZENT Stream+ water flosser has several pressure settings, from gentle to more powerful, so you can adjust it to the current condition of your gums. This is a home-use device, not a medical device. It effectively supports daily hygiene, but does not replace treatment or regular visits to the dentist.

How should you clean your tongue when you have a canker sore?

The tongue also needs gentle cleaning, especially if the canker sore is elsewhere in the mouth and tongue coating could encourage bacteria to multiply. If the sore is on the tongue, take extra care: clean it gently, avoiding the painful area, and don’t scrub too hard.

See also: Tonsil stone removal: which methods are effective and safe?

What should you avoid when you have canker sores?

A practical list to help keep the discomfort from lasting longer.

Don’t irritate the sore while brushing

Avoid brushing directly over the sore, and don’t press the bristles against it.

Avoid hard and sharp-edged foods

Chips, toast, nuts, bread crusts and raw vegetables with sharp edges can further injure the already irritated oral mucosa.

Avoid very hot and irritating foods and drinks

Hot drinks and foods, as well as very acidic, salty or spicy foods, can make the burning and pain at the sore worse.

Don’t try to remove a canker sore mechanically

Touching, scratching or trying to remove a canker sore with a fingernail or another object won’t speed up healing and may cause further irritation.

How can you prevent canker sores from coming back?

Since canker sores recur in some people, it’s worth looking at daily habits that may reduce how often they occur.

Regular, gentle oral hygiene

Brushing regularly but gently and cleaning between your teeth helps limit plaque buildup, which can itself irritate the oral mucosa.

Protecting the oral mucosa from injury

Pay attention to your brushing technique and avoid applying too much pressure. Avoid biting your cheeks or chewing on pens, and if your braces have sharp edges, ask your orthodontist about ways to protect your mouth.

Tracking canker sore triggers

If you notice that canker sores appear after certain situations, such as intense stress, specific foods or exhaustion, it’s worth keeping track. These personal notes can also be helpful when speaking with a doctor or dentist if the sores keep coming back.

When should you consult a professional about recurring canker sores?

A single, occasional canker sore usually does not require a visit to a specialist. It is different when canker sores appear regularly, every few weeks, and start to significantly affect your comfort while eating or speaking. In that case, it is worth discussing with a doctor or dentist to check whether something more than typical, occasional irritation is causing them.

See also: Bad breath despite brushing your teeth: causes

When should you see a doctor or dentist about a canker sore?

A typical canker sore is short-lived, harmless, and goes away on its own. However, there are situations when a sore in the mouth needs to be assessed by a specialist, not just treated at home. It is worth consulting a doctor or dentist if you experience:

• the sore persists for a long time, much longer than usual,
• frequent recurrences of canker sores,
• very large or numerous canker sores appearing at the same time,
• severe pain disproportionate to the size of the sore,
• trouble eating or drinking,
• an unusual appearance, unlike usual,
• no improvement over time.

None of the points above are grounds for self-diagnosis. They are just guidelines on when it is worth showing the sore to a specialist rather than waiting and hoping it will go away on its own.

Canker sores: frequently asked questions

What is a canker sore?

A canker sore is a small, painful ulcer of the oral mucosa, usually white-yellow in the center and surrounded by a red border. It is one of the most common, harmless changes in the mouth and usually heals on its own within a few days to a couple of weeks.

What helps with canker sores in the mouth?

The most important thing is to be gentle: avoid sharp, hard, very hot, and spicy foods; limit further irritation of the sore; and maintain gentle but regular oral hygiene while it heals.

Can you brush your teeth when you have a canker sore?

Yes, you can brush gently, avoiding direct contact with the sore spot. Skipping toothbrushing does not help it heal and encourages plaque to build up.

Is a canker sore on the tongue normal?

Yes, the tongue is one of the more common places for canker sores to appear. They can be particularly bothersome because the tongue is constantly moving while you eat and speak, but the recommended care is the same as for canker sores in other locations.

What does a canker sore on the gum near a tooth mean?

A canker sore on the gum near a tooth looks similar to one in other locations: it is a small, painful ulcer with a light-colored center. If the sore looks unusual, is very painful, or does not go away over time, it is worth consulting a dentist.

Canker sores are common, though unpleasant, for most of us. Gentle brushing, careful use of a water flosser, and patience are usually enough to wait for them to heal. However, if canker sores keep coming back or behave unusually, the best step is to talk to a dentist.

See also: Gingivitis - symptoms, causes, and what helps