Mouth sores

Mouth sores occur when the lining of the mouth is damaged following chemotherapy or localised radiation therapy.

What causes mouth sores?

The lining of the mouth and throat has a rapid cell turnover rate, making it susceptible to chemotherapy.

All chemotherapy drugs have the potential to cause mouth sores. The extent of damage depends on the drug and dosage.

Other factors which contribute to mouth sores include neutropenia (low white blood cell count), infections in the mouth/throat, poor oral hygiene and smoking.

What are the signs and symptoms of mouth sores?

Mouth sores typically occur two to three weeks from the start of chemotherapy and/or radiation therapy treatment, and may last for two to three weeks after completion of treatment. Onset is more rapid and symptoms may be more severe if you receive chemotherapy and radiation therapy at the same time.

  • Pain in the mouth and throat
  • Redness of your inner cheek or soft palate
  • Burning sensation and difficulty swallowing with or without eating/drinking
  • Loss of senses such as altered saliva and altered taste
  • Bleeding from the mouth
  • Infection in the mouth

How can mouth sores be prevented/managed?

In some circumstances, the use of ice chips or ice-cold water may assist in the prevention of mouth sores. Your care team will discuss this with you if it is appropriate in your clinical situation. Good oral hygiene and treatment of symptoms are key to managing the effects of mouth sores.

  • If you have pain, you may be offered topical analgesia (i.e. mouthwash) or systemic medication which should be taken regularly
  • Rinse mouth after each meal (at a minimum) and before bed with a bland mouth rinse – Half teaspoon of salt to one glass (200mL) water or one teaspoon of sodium bicarbonate to one glass (200mL) water
  • Consider strategies to quit smoking
  • Maintain good oral intake, as able – Ensure you drink plenty of water and other beverages, eat a soft, minced or pureed diet, add extra sauces or gravies to moisten meals, avoid foods that are acidic, hot, coarse or hard, and salty or spicy, consume small, frequent, high protein, high energy meals, consider talking to a dietitian who can support you to manage your diet
  • Maintain good oral care, as able – Brush your teeth with a soft or electric toothbrush after meals and before bed, replace toothbrush regularly to minimise infection, if flossing is routine continue this at least daily, avoid flossing if you’re at risk of thrombocytopenia (low platelets) as this may irritate your gums and cause bleeding, moisten lips with Vaseline, soft paraffin or lip balm, and ensure regular cleaning of dentures and removal of dentures before bed

When should I seek help from a health professional?

It’s important to report the development or worsening of any symptoms related to mouth sores. If you notice any of the following changes, contact your care team:

  • Increasing pain in the mouth, jaw or throat
  • Mouth ulcers
  • White patches on mucous membranes or tongue (thrush)
  • Difficulty swallowing
  • Bleeding from the gums or mouth
  • Temperature of 38oC or higher


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