Cancer treatment may cause a number of different mouth problems. See below for types of problems, why they happen and how to cope.

What types of mouth problems does cancer treatment cause and why?

Mouth problems in cancer care are not inevitable. It depends on the type of cancer and treatment you’ve had. 

Probably the commonest issues are sore mouth and mouth infections. These are most often caused by chemotherapy but also by radiotherapy to the head and neck. Cancer treatment affects any body tissue where the cells renew themselves frequently. That means healthy cells that multiply often are more likely to be damaged or killed, including the lining of the digestive system, from the mouth onward. Treatment also lowers your resistance to infection. So any sore or broken down areas in the lining of your mouth are more likely to become infected.

Radiotherapy to the head and neck can cause a dry mouth. The radiotherapy can affect your salivary glands, meaning that you are producing less saliva than usual. Some painkillers and anti-sickness drugs can also cause dry mouth. As well as making it more difficult to eat, a dry mouth is more likely to become sore and infected.

If you have a cancer in your head, neck or throat, your treatment may make it difficult to swallow for a while. This may be caused by surgery or radiotherapy causing temporary swelling. If chemotherapy has caused a very sore mouth with mouth ulcers, this can spread to your oesophagus and make swallowing painful.

Radiotherapy or surgery to the head and neck can cause stiffness in the muscles you use to open and close your mouth.

There are sections below on each of these problems as well as tips on how to manage them.

Sore mouth and infections

If cancer treatment is affecting your mouth, the skin inside may become inflamed and sore. This is called mucositis. You may also develop mouth ulcers because your mouth is sore, because you are run down or as a direct side effect of some cancer drugs. Your doctor may try to prevent infections developing by giving you antibiotic lozenges to suck or anti-fungal mouthwashes. You can help by looking after your mouth as well as you can before and throughout your treatment. Here are some tips:

  • It’s important to try and keep your mouth clean – clean your teeth, tongue and gums after eating and before you go to bed
  • A child or baby toothbrush is often softer than an adult one and can help ease pain when brushing
  • Use an alcohol-free mouthwash
  • If cleaning your teeth is too painful for sore gums, use a gauze or sponge swab soaked in mouthwash
  • Try to keep your mouth moist – drink regularly, try sugar-free gum and if necessary, use a humidifier at night
  • Keep your lips moisturised with lip salve
  • If you wear false teeth and your mouth is sore, only put them in to eat
  • If your mouth is sore, eat soft foods and have food and drinks warm rather than very hot or cold

  • Spicy food and acidic fruit juice drinks may make soreness worse
  • Check your mouth for cracks, red or white patches, spots, sores and bleeding - and if you find anything tell your doctor!
  • Avoid flossing your teeth as this can cause extra pain and damage to the cells in the mouth. 

A sore mouth can be very painful so do tell your doctor or nurse as soon as you start having problems. They will give you painkillers and even mouthwash with a local anaesthetic to numb your mouth. Do take painkillers as prescribed. It will make it easier for you to eat and drink - and that will help you get better.  

Dry mouth

Doctors call dry mouth ‘xerostomia’ (zero-stow-mee-ah). You may have less saliva or it may be thick, sticky and whiter than usual. A dry mouth increases your risk of soreness and infections, so all the info on that also applies. Alcohol, tobacco, caffeine and sugary drinks can all make it worse so are best avoided. Your doctor can prescribe artificial saliva as a gel or spray. It may also help to:

  • Rinse your mouth at least every two hours
  • Suck ice chips and take frequent sips of water
  • Chew sugar-free gum or suck sugar-free sweets (be careful if they’re for diabetics – too many will give you diarrhoea)
  • Add liquid to dry foods – lots of gravy or sauces, yoghurt or thin cream
  • Sip drinks with meals
  • Use a humidifier at night – or put a bowl of clean water next to a radiator

Difficulty swallowing

This can happen because your throat is sore or because of swelling related to your cancer or treatment. A dry mouth also makes it harder to swallow. A less common reason is surgery to your throat affecting the muscles you normally use to swallow. 

Managing this will depend on the cause, so it’s best to speak to your doctor or specialist nurse. The tips above on sore or dry mouth may help. If you feel as if food is getting stuck, a soft diet may suit you better – soups, stews, porridge, and sauces and custard to moisten foods. Little and often may be easier if you’re finding eating a trial. Do ask to be referred to a dietitian. They will have lots of helpful advice.

Jaw stiffness (Trismus)

If your jaw muscles become stiff after surgery or radiotherapy, it can affect your speech, ability to eat and mouth hygiene. It can come on weeks or even months after radiotherapy to the head and neck. This doesn’t happen to everyone but if you do develop it, tell your cancer specialist. The sooner you get some treatment, the better. If you leave it, it can get worse.

You can tell if your jaw muscles are stiffening by measuring how many fingers you can get in your mouth. Three fingers (vertically) means your jaw is opening normally. 

If you have trismus, your specialist will refer you to a physio or speech therapist. They will give you exercises to stretch your jaw muscles. There are also devices such as ‘Therabite’ which you can use to stretch the jaw.


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