Canker Sores in Kids — Causes, Treatment, and When to See a Doctor

TL;DR

Canker sores are common in children and often start in childhood or the teen years. In a large US survey, about 1 in 5 children and teens had had one in the past year, and about 2 in 5 had had one at some point (Shulman, 2004 — J Oral Pathol Med). Before assuming it's a canker sore, though, rule out the usual look-alikes in young kids: hand, foot, and mouth disease and herpangina (sores at the back of the mouth, often with a rash on the hands and feet), and a first herpes infection (many sores plus swollen, bleeding gums and fever). If your child gets mouth sores together with fever on a regular schedule, every three to six weeks or so, ask the pediatrician about PFAPA syndrome and cyclic neutropenia. For ordinary canker sores, an SLS-free toothpaste, salt water rinses for kids who can spit, and barrier patches are safe. Don't use benzocaine numbing gels in children under 2. And if a child gets sores often, a blood test for iron, B12, and folate, and a celiac screen, are worth asking for.

How Common Are Canker Sores in Children?

Common. A study combining two large US surveys of more than 50,000 children and teens found that about 1.5% had a canker sore on the day they were examined, about 20% had had one in the past year, and about 40% had had one at some point in their lives (Shulman, 2004 — J Oral Pathol Med).

Recurring canker sores usually start in childhood or adolescence, and many adults who get them can remember having them as kids. An occasional canker sore in a child isn't a sign that something is wrong.

What's different with kids is practical. Young children can't always tell you what hurts, they may stop eating or drinking because of the pain, and they get a few viral infections that look a lot like canker sores.

Is It Actually a Canker Sore? The Common Look-Alikes

In toddlers and young children, mouth sores are more often caused by a virus than by canker sores. The location of the sores and the other symptoms are the best clues (PMID: 35937022).

Hand, foot, and mouth disease and herpangina

These are caused by related viruses and are extremely common in daycare and preschool. Kids get painful sores in the mouth, usually with fever, and in hand, foot, and mouth disease, a rash or small blisters on the palms and soles. They're contagious and get better on their own in about a week. The main job is keeping your child drinking.

A first herpes infection (primary herpetic gingivostomatitis)

The first time a young child catches the cold sore virus, it often causes many painful sores throughout the mouth, very swollen and bleeding gums, high fever, and refusal to eat or drink. The gums are the giveaway: canker sores don't do that. Children with this can get dehydrated quickly. Call the pediatrician, especially early on, since antiviral medicine works best in the first few days.

Mouth Sores With Fever on a Schedule

If your child gets mouth sores along with fevers that come back on a fairly regular schedule, every few weeks, there are two conditions to ask the pediatrician about.

PFAPA syndrome

PFAPA stands for Periodic Fever, Aphthous stomatitis (canker sores), Pharyngitis (sore throat), and Adenitis (swollen neck glands). It's the most common cause of regularly recurring fevers in young children.

What it looks like:

• High fevers, often around 40°C (104°F), lasting several days, returning roughly every three to six weeks. In the original description of the syndrome, the average was about every four weeks (Thomas et al., 1999 — PMID: 10393598).
• Sore throat and swollen neck glands with most episodes
• Canker sores in only some episodes. In one study of 105 children, they showed up in 38% (Feder & Salazar, 2010 — PMID: 19889105). So a child can have PFAPA even if the mouth sores aren't there every time.
• Completely well between episodes, growing normally
• Usually starting before age 5

Parents often say they can predict the next episode on a calendar. Many children get several rounds of strep tests and antibiotics before anyone notices the pattern.

Treatment. A single dose of a steroid like prednisone at the start of an episode usually stops the fever quickly, though in some children it makes the next episode come sooner (Feder & Salazar, 2010 — PMID: 19889105). Removing the tonsils resolves PFAPA in many children. In one trial, 63% of children who had their tonsils out had complete resolution compared with 5% who didn't (Garavello et al., 2009 — PMID: 19464029), and a Cochrane review rated the evidence for tonsillectomy as moderate (PMID: 31886897). Most children grow out of PFAPA eventually, even without treatment.

Cyclic neutropenia

This is much rarer than PFAPA but important not to miss. In cyclic neutropenia, a type of white blood cell (neutrophils) drops to very low levels about every three weeks, then recovers. During the low points, children get fevers, mouth sores, and infections (PMID: 20301705).

It can look a lot like PFAPA. The difference shows up on blood tests: a single blood count can easily miss the low point, so doctors check blood counts two or three times a week over several weeks to see whether neutrophils drop and recover in a cycle. If your child has regular fevers with mouth sores, it's reasonable to ask whether cyclic neutropenia has been ruled out.

What Causes Canker Sores in Kids

The causes are mostly the same as in adults. A few are worth extra attention in children.

Picky eating and nutrient gaps

Low iron, B12, folate, and zinc are all linked to canker sores. Kids with very limited diets, kids who don't eat meat, and kids who drink a lot of milk (which can crowd out iron-rich foods and interfere with iron absorption) are at higher risk for some of these. If your child gets sores often, ask the pediatrician to check iron (including ferritin), B12, and folate.

If a deficiency is found, the pediatrician should set the dose. Don't give a child adult-dose supplements. B12 is very safe, but zinc and especially iron can cause real harm at the wrong dose, and iron supplements are a well-known cause of serious poisoning in young children. Keep all supplements out of reach.

Celiac disease

Canker sores are more common in children with celiac disease, especially before they're diagnosed. In one study of 97 children with celiac disease, 47% of newly diagnosed, untreated children had canker sores, and they tended to improve on a gluten-free diet (PMID: 41474653). Looking at it from the other direction, among 108 children with recurring canker sores, about 3% turned out to have celiac disease (PMID: 31957941).

That's a small percentage, but celiac disease is worth checking for in a child with frequent canker sores, especially if there's also stomach pain, diarrhea, constipation, poor growth, or low iron. The test is a blood test (tissue transglutaminase IgA). Don't start a gluten-free diet before testing, because it can make the test come back falsely negative. See Gluten and Canker Sores.

Other conditions

Crohn's disease can show up first in the mouth, especially in children, sometimes as lip swelling or unusual sores rather than ordinary canker sores. See Canker Sores and Crohn's Disease. Behçet's disease, which causes mouth and genital sores, is rare in children but possible.

Braces, sharp teeth, and biting

Braces and retainers rub. So do newly erupting or chipped teeth. Kids also chew their cheeks and lips, and often bite a numb lip after a dental visit. See Canker Sores From Braces and Canker Sores After Dental Work.

Puberty and stress

Canker sores often get more frequent in the teen years, and exam stress and poor sleep can trigger them. See Stress and Canker Sores and Sleep and Canker Sores.

Treating Canker Sores in Children

SLS-free toothpaste: safe at any age

Most toothpastes contain sodium lauryl sulfate (SLS), a foaming detergent that's linked to canker sores. Switching to an SLS-free toothpaste is the easiest preventive step for a child who gets them often. Use the usual amount of fluoride toothpaste for your child's age (a rice-grain smear under 3, a pea-sized amount from 3 to 6). See SLS-Free Toothpaste for Canker Sores.

Salt water rinse: once they can spit

A quarter teaspoon of salt in a cup of warm water is soothing and safe for kids who can reliably swish and spit, usually around age 6 and up. Swallowing a little won't hurt them. See Salt Water Rinse for Canker Sores.

Barrier patches: for kids who'll leave them alone

Dissolving patches cover the sore and make eating less painful. They don't contain medicine. The catch is that younger kids tend to poke at them with their tongue, so they work best in older children.

Benzocaine numbing gels: not under 2

In 2018, the FDA asked manufacturers to stop selling benzocaine teething products for children under 2 and required warnings on other oral benzocaine products. Benzocaine can cause a rare but dangerous blood problem called methemoglobinemia, where the blood can't carry oxygen properly, and the FDA said these products offer little benefit for teething. For children 2 and older, follow the label carefully and use the smallest amount for the shortest time.

Pain relief by mouth

For a child in real pain, especially before meals, children's acetaminophen or ibuprofen at the correct dose for their weight is usually the most practical option. Cold, soft foods (yogurt, smoothies, applesauce, popsicles) and avoiding salty, acidic, and crunchy foods help too. Using a straw can keep drinks off the sore.

Prescription treatment

For a severe or frequent sore, a pediatric dentist or pediatrician can prescribe a steroid gel or paste. Use it only as directed.

Keep them drinking

The biggest risk with painful mouth sores in young children isn't the sore itself. It's refusing to drink. Signs of dehydration include fewer wet diapers or trips to the bathroom, a dry mouth, no tears when crying, unusual sleepiness, or dark urine.

For more treatment options, most of which apply to older children and teens as well, see The Fastest Way to Heal a Canker Sore.

When to Call the Doctor

Call the same day if your child:

• Won't drink, or shows signs of dehydration
• Has many sores throughout the mouth with swollen, bleeding gums and fever
• Seems very unwell, has trouble breathing or swallowing, or is drooling heavily

Make an appointment if your child:

• Gets mouth sores along with fevers that come back on a regular schedule
• Gets canker sores often, or several at once
• Has a sore larger than about 1 cm, or one that hasn't healed in three weeks
• Has mouth sores plus stomach symptoms, poor growth, or tiredness
• Has lip swelling, sores in unusual places, or sores on the genitals