Canker Sores in Kids: Causes and How to Soothe Them

Editorially reviewed by the Dental.me Editorial Team · Updated July 2026

If your child suddenly refuses to eat and points to a small, angry-looking sore inside their mouth, take a breath — you are almost certainly looking at a canker sore. Canker sores (doctors call them aphthous ulcers) are one of the most common mouth complaints in childhood. They are harmless, they are not contagious, and the vast majority heal completely on their own within a week or two. This guide walks you through what they look like, what triggers them, and the simple things you can do at home to make your child more comfortable while they heal.

What canker sores in kids actually are

A canker sore is a small, shallow ulcer that forms on the soft tissue inside the mouth. You will usually spot it on the inner lips, the inside of the cheeks, the tongue, the gums, or the floor of the mouth. They tend to be round or oval, with a white or yellowish center and a red border around the edge.

Here is the most reassuring part: canker sores are not caused by an infection you can catch or spread. Your child did not pick one up from another kid, and they cannot pass one to a sibling by sharing a cup. They can sting quite a bit — especially while eating or drinking — but they are not dangerous, and they typically heal in about one to two weeks without leaving a scar. Many children get them from time to time, and some are simply more prone to them than others.

Canker sore or cold sore? The difference that matters

Parents mix these two up constantly, and the distinction genuinely matters. The simplest rule of thumb is location. A canker sore lives inside the mouth and is not contagious. A cold sore appears on or around the outside of the lips, is caused by a virus (herpes simplex), and is contagious — it can spread through kissing or shared utensils and drinks.

So if you see a blister or crust on the outside of the lip, that points toward a cold sore, not a canker sore. If the sore is tucked inside the cheek or under the tongue, canker sore is the far more likely answer. We break the two down side by side in our guide on canker sores vs. cold sores. And if your child also has sores on the hands or feet along with a fever, that pattern can point to a different cause entirely — our guide to hand, foot, and mouth disease covers what to look for.

How to soothe a canker sore at home

Most of what your child needs is comfort while the sore heals itself. A few practical steps go a long way:

• Offer cool, soft, bland foods. Think yogurt, applesauce, mashed potatoes, smoothies, and cold drinks. Popsicles are a favorite — the cold numbs the sore and encourages fluids at the same time.
• Avoid the foods that sting. Skip acidic items (citrus, orange juice, tomato sauce), spicy dishes, very salty snacks, and hard or crunchy foods with sharp edges. These can turn one painful bite into tears.
• Try a gentle rinse. For a child old enough to swish and spit reliably, a warm salt-water or baking-soda rinse can ease discomfort and keep the area clean.
• Use an age-appropriate oral gel or rinse. Over-the-counter numbing gels made for children can dull the pain — just follow the label for your child’s age and never exceed the directions.
• Keep brushing gently. A soft-bristled brush and a light touch keep the mouth clean without re-irritating the sore. An SLS-free toothpaste can be kinder if sores are a recurring problem.
• Manage pain if needed. Age-appropriate acetaminophen or ibuprofen can help at mealtimes or bedtime when the sting is worst.

One thing to watch closely: because eating and drinking hurt, some kids quietly cut back on fluids. Keep offering cold drinks and popsicles and watch for signs of dehydration. And remind your child not to poke or pick at the sore, which only slows healing. For more comfort ideas, see our roundup of canker sore remedies. If the whole tongue feels sore rather than one distinct spot, our piece on sore tongue causes may fit better.

What causes canker sores in kids

Often there is no single, obvious cause — and that is normal. Canker sores usually show up when a mix of small factors line up. The common triggers in children include:

• Minor mouth injury: biting the cheek or tongue, a sharp tooth, braces or a bracket rubbing, or brushing too aggressively.
• Trigger foods: acidic or spicy foods can spark a sore in kids who are prone to them.
• Stress and being run-down: a hard week at school, poor sleep, or generally being worn out can bring sores on.
• Certain toothpastes: those containing sodium lauryl sulfate (SLS) seem to trigger sores in some children.
• Food sensitivities and nutrition: occasionally low levels of iron, vitamin B12, or folate play a role.
• Family tendency: canker sores often run in families, so a child of a frequent sufferer may get them too.

How to help prevent them coming back

You cannot always stop canker sores, but you can reduce how often they appear. If braces or a sharp edge is the culprit, orthodontic wax over the offending spot protects the tissue. Encourage gentle brushing with a soft brush, and switch to an SLS-free toothpaste if sores keep returning. Help your child get enough rest and manage stress — if worry or nerves seem to be a pattern, our guide on dental anxiety in children offers calming strategies that apply well beyond the dentist’s chair. Finally, if you notice specific foods reliably bring on a sore, it is reasonable to limit them.

When to see a dentist or doctor

The great majority of canker sores are minor and clear up on their own. Reach out to a dentist or doctor if you notice any of the following:

• A sore that is unusually large.
• A sore that lasts longer than about two weeks.
• Sores that keep coming back frequently.
• A high fever, or a child who seems generally unwell.
• Sores that spread to the outside of the mouth, or any time you are not sure it is a canker sore.
• Signs of dehydration from not drinking enough.
• Very frequent sores — a professional can check for an underlying cause such as a nutritional deficiency.

None of these mean something is seriously wrong; they simply signal it is worth a professional set of eyes to be sure and to rule out anything treatable.

The takeaway

Canker sores in kids are common, harmless, non-contagious ulcers that form inside the mouth and heal on their own in about one to two weeks. Soothe them with cool, soft, bland foods, gentle mouth care, and age-appropriate over-the-counter relief, keep your child drinking so they stay hydrated, and steer clear of the acidic and spicy foods that sting. Remember the key distinction: inside the mouth and not contagious means canker sore, while a sore on or around the lips points to a cold sore. And if a sore is large, lingers past two weeks, keeps recurring, or comes with a fever, check in with your dentist or doctor for peace of mind.

Find care near you: compare dentists in your area, or browse dental specialties.