How radiotherapy to the head and neck can affect your mouth

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

  • sore mouth and throat (mucositis)
  • dry mouth (xerostomia)
  • bad breath
  • thick, sticky saliva (mucus)
  • difficulty swallowing
  • changes to eating and drinking
  • taste changes
  • hoarseness.

Side effects usually begin to develop after one to two weeks of radiotherapy. They may get worse for some days after treatment ends before gradually improving. Most people find that side effects have improved 6–12 weeks after radiotherapy.

Sometimes, radiotherapy causes long-lasting or permanent side effects. These are less common and 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.

You will have a team of specialists to help you look after your mouth before and during treatment. They can help you manage temporary and late side effects.

Side effects of radiotherapy to the head and neck

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 severe, depending on:

  • the area of the head and neck treated
  • the dose of radiotherapy
  • the length of your treatment.

They are usually more severe if you have radiotherapy combined with chemotherapy (chemoradiation).

Side effects usually begin to develop after one to 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 6–12 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 late or long-term 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.

Who can help

There will be several specialists in your team who can give you advice and treatments to help different mouth problems. You may meet some of them before you start radiotherapy. Others you may meet during or after treatment. Your team may include:

  • Specialist doctor – you can talk to them about any problems you have and they can help or refer you to a different member of the team.
  • Therapeutic radiographers – they will plan and give your radiotherapy treatment, and will be able to talk about potential side effects and how to cope with them.
  • Dietitians – they can help you meet your nutritional needs.
  • Speech and language therapists (SLTs) – they assess problems with speech, voice and swallowing and teach you how to manage them.
  • Dentists and dental hygienists – they teach you how to keep your mouth clean and prevent tooth decay.
  • Specialist nurses – they give information and support on managing side effects.
  • Psychologist or counsellors – they can help you adjust to changes after treatment.

Temporary side effects

Sore mouth and throat (mucositis)

Your mouth and throat are likely to become sore after a couple of weeks of treatment. You may develop mouth ulcers. Soreness and ulceration of the lining of the mouth or throat is called mucositis and can be very painful. Talk to your doctor about different types of pain relief and what might be suitable for you.

Dry mouth (xerostomia)

Radiotherapy can affect the salivary glands and you may not make as much saliva as before. This can make your mouth and throat dry, which makes eating, drinking 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.

Your doctor can prescribe drugs to stimulate saliva. There also artificial saliva products that can help moisten the mouth.

Thick, sticky saliva (mucus)

Radiotherapy can change the consistency of your saliva. It may become thicker, stringy and sticky, like mucus. The mucus does not 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.

Using a salt water mouth wash regularly can help maintain oral hygiene. You should rinse your mouth out with salt water four times a day, after each meal and before bed. Some mouthwashes can also help, but you should avoid any that have alcohol in.

Changes in your saliva usually get better within about eight weeks of radiotherapy ending. But sometimes the changes continue for several months or longer. If the mucus continues, medicines can be prescribed to reduce the amount you make.

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. This is a common side effect of radiotherapy treatment and can be treated with antibiotic or antifungal medicine.

Difficulty swallowing

Radiotherapy to the head or neck area can cause pain and swelling in the mouth or throat. If you are having problems with swallowing, ask to see a speech and language therapist. They can assess your swallowing and give helpful advice. They will encourage you to continue swallowing for as long as you can, even if it is just sips of water. This is to maintain a swallow action and will help with your recovery.

Changes to eating and drinking

If you’re having problems eating and drinking because of mouth problems, you may see a dietitian for more support. 

What might help:

  • Sipping cool drinks throughout the day.
  • Choosing foods that taste good and are easy to eat.
  • Moistening food with gravy and mild sauces.
  • Trying to have more liquid and semi-solid meals.

If chewing or swallowing is painful, your doctor may prescribe medication to help control these symptoms.

Taste changes

Radiotherapy can affect your taste buds, so you may notice changes in the way your food tastes. Some people have described food having a metallic taste. You may find all food tastes the same. It is also possible to temporarily lose your sense of taste during radiotherapy treatment.


If hoarseness occurs, it may be helpful to rest your voice some of the time. Hoarseness should improve after radiotherapy treatment is finished.

Possible late 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. Some people will have a dry mouth permanently.

Saliva protects our teeth against decay. If you have less or no saliva in your mouth, the risk of tooth decay is higher. It is important to protect your teeth by following a mouth care routine. You should also see an oral hygienist and dentist regularly. They can show you how to keep your mouth and teeth clean, and pick up any problems early. Your specialist team may prescribe a high fluoride toothpaste to help maintain good oral hygiene and prevent tooth decay.

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 will be shown gentle mouth-opening exercises that can help to prevent or relieve problems. There are also specialist aids that can 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