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Healthy Children > Tips & Tools > KidsDoc Symptom Checker > symptomviewer
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Mouth Ulcers

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Definition

  • Painful, shallow ulcers (sores) on the lining of the mouth
  • Found on the gums, inner lips, inner cheeks, or tongue
  • Sores only on the outer lips (such as cold sores) are not covered

Causes of Mouth Ulcers or Sores

  • Canker Sores. The main cause of 1 or 2 mouth ulcers after age 5.
  • Hand-Foot-Mouth Disease. The most common cause of multiple ulcers in the mouth. These ulcers are mainly on the tongue and sides of the mouth. Most children also have small deep blisters on the palms and soles. Due to the Coxsackie virus. It is common between ages 1 to 5 years.
  • Herpes Simplex Virus Infection. The first infection with the herpes cold sore virus can be severe. It can cause 10 or more ulcers on the gums, tongue and lips. Key findings are additional ulcers on the outer lips or skin around the mouth. Also causes fever, pain and trouble swallowing. Usually occurs age 1 to 3. It usually follows contact with an adult who has active cold sores (fever blisters). Often they have kissed the child.
  • Recurrent Cold Sores (Fever Blisters). Sores are only found outside the mouth on the outer lip. They may recur 2 or 3 times a year in the same place. There are no ulcers inside the mouth. Adult cold sores are the cause of Herpes Simplex infections in young children. Occurs in 20% of teens and adults.
  • Mouth Injury. Common mouth injuries are biting the tongue or inside of the cheek. Others can be caused by a toothbrush. The lining of the mouth always looks white when it heals. So forgotten injuries can look like a canker sore.
  • Mouth Burns. Hot foods (such as pizza) can cause mouth sores. They also turn white as they heal.

Causes of Canker Sores

  • Canker sores have many causes.
  • Minor injuries to the mouth can trigger a canker sore. Examples are from a rough food or a hard toothbrush. Biting oneself while chewing can start one.
  • Food allergies or irritants may also be a trigger.
  • Vitamin deficiencies can also be a cause. A vitamin deficiency can occur if your child is a picky eater.
  • Canker sores can run in families (genetic).
  • Often, the cause is unknown.

Symptoms of Canker Sores

  • Small ulcers have a white center with a red border around them
  • Size is usually less than ¼ inch (6 mm)
  • Found on the inner lips and inner cheeks
  • The sores are very painful, even when not eating
  • Usually get 1 canker sore at a time. Sometimes get 2 or 3.
  • No fever or other symptoms
Barton Schmitt MD, FAAP
Disclaimer: this health information is for educational purposes only. You, the reader, assume full responsibility for how you choose to use it.
Copyright 2000-2025 Schmitt Pediatric Guidelines LLC.
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