How radiotherapy can affect your mouth

Radiotherapy to the head and neck can cause mouth problems including:

  • Sore mouth and throat
  • Dry mouth
  • Bad breath
  • Thick, sticky saliva (mucus).

These side effects usually get better gradually after you finish treatment.

Sometimes, radiotherapy causes long-lasting or permanent side effects. These are less common but may happen months or years after treatment. Two of the most common late effects are a dry mouth and an increased risk of tooth decay. Your specialist can tell you whether your treatment may cause any late effects.

There are things you can do to keep your mouth healthy during and after treatment. Let your specialist doctor or nurse know if you are having mouth problems. They can give you advice and treatments to help.

If you’re having problems eating and drinking because of mouth problems you may see a dietitian for more support. We also have information about coping with eating problems.

Side effects of radiotherapy

Radiotherapy to the head and neck can cause temporary side effects such as a sore mouth or throat and difficulty swallowing. Side effects can be mild or more troublesome, depending on the dose of radiotherapy and the length of your treatment. They are usually more severe if you have radiotherapy combined with chemotherapy.

Side effects usually begin to develop after about two weeks of radiotherapy. They may continue to get worse for 7-10 days after treatment ends before gradually improving. Most people find that side effects have noticeably improved 6-8 weeks after radiotherapy has ended.

Sometimes radiotherapy can cause long-lasting side effects or new side effects that develop months or even years later. These are called long-term or late effects. Two of the most common late effects are a dry mouth and an increased risk of tooth decay. Your specialist can tell you whether your treatment may cause any late effects.

There are things you can do to keep your mouth healthy during and after treatment. Let your specialist doctor or nurse know if you are having mouth problems. They can give you advice and treatments to help.

If you’re having problems eating and drinking because of mouth problems you may see a dietitian for more support. We also have information about coping with eating problems.


Temporary side effects

Sore mouth and throat

Your mouth and throat are likely to become sore after a couple of weeks of treatment and you may develop mouth ulcers.

Dry mouth

Radiotherapy can affect the salivary glands, so you may notice that you don’t make as much saliva as before. Your mouth and throat may become dry. This can make eating and speaking more difficult.

After a few months you may begin to make saliva again, but it may not be as much as before. Sometimes the salivary glands don’t recover, which leaves the mouth permanently dry.

Thick, sticky saliva (mucus)

Radiotherapy can change the consistency of your saliva. It may become thicker, stringy and sticky, like mucus. The mucus doesn’t flow as well as normal saliva so it may build up in your mouth and throat. You may feel the need to spit frequently to get rid of the mucus build-up, so it’s a good idea to keep tissues handy.

Changes in your saliva usually get better within about eight weeks of radiotherapy ending but sometimes continue for several months or longer. If the mucus continues, there are medicines that can be prescribed to reduce the amount you make. Tell your cancer specialist or nurse if you’re having difficulties.

Bad breath

This is usually caused by changes to your saliva and can be reduced by regular mouth care. It may also be caused by an infection in your mouth, which is common during radiotherapy treatment. If you have an infection, it can be treated with antibiotic or antifungal medicine.


Possible late (long-term) effects of radiotherapy

Dry mouth and tooth decay

After treatment, the salivary glands may gradually begin to make saliva again. But your mouth may still be drier than it was before treatment and some people will have a dry mouth permanently.

Saliva protects our teeth against decay. If you have less or no saliva in your mouth, you have a much higher risk of tooth decay. This means it’s really important to protect your teeth by following a mouth care routine and seeing an oral hygienist and dentist regularly.

Difficulty opening your mouth due to a stiff jaw (trismus)

After radiotherapy to the head and neck, the muscles that open and close your mouth can become stiff. You’ll be shown gentle mouth-opening exercises that can help to prevent or relieve problems. There are also specialist aids available to help you exercise your jaw.

Your doctor, specialist dentist, or speech and language therapist can give you advice about exercises and the possible benefits of using an exercise aid.


Back to Mouth problems