Mouth problems and cancer treatment

Both cancer and its treatment can cause mouth problems.

The chance of you developing problems depends on where your cancer is and your type of treatment. Some people get mouth problems during or after chemotherapy or targeted drugs. It’s particularly common if you have high dose chemotherapy and a stem cell transplant. And most people who have radiotherapy to the head and neck will develop problems with their mouth.

Mouth problems are often mild. But they can sometimes become serious and affect your daily life.

Looking after your mouth

You can help prevent some mouth problems by keeping your mouth clean and moist. For example, gently cleaning your teeth or dentures in the morning, evening, and after each meal. You can use lip balm to keep your lips moist.

Looking after your mouth might not keep problems away altogether. So do talk to your healthcare team if you have symptoms such as a dry, sore mouth or taste changes. There are things you can do to help relieve these symptoms and your team can prescribe medicines if you need them.

Sore mouth and ulcers

Chemotherapy, targeted drugs, immunotherapy and radiotherapy work by killing cancer cells or stopping them from growing. But they usually affect some healthy cells too. And the cells that line your mouth are very sensitive to the effects of cancer treatments.

These treatments might make the lining of your mouth inflamed and sore. This is called mucositis. They can also cause small but sometimes very painful sores (ulcers) in the moist tissues inside the mouth. You might also have sores (ulcers) on your tongue.

Mouth ulcers are most likely to develop about 5 to 10 days after chemotherapy starts. They start a bit later with radiotherapy to the mouth and usually go away soon after your treatment finishes. Ulcers caused by targeted drugs may happen several weeks or months after the first dose. You can also get mouth ulcers if you’re run down or not eating properly.

Tell your doctor straight away if your mouth or gums are really sore and painful. You are not making a fuss. You might need to have strong painkillers. If the pain in your mouth is very bad and you cannot swallow, you might need a morphine drip for a short time while you recover.

A stem cell or bone marrow transplant can cause a very sore mouth. Sometimes your mouth might be too sore to eat. If this happens, you may need to have support with drip or tube feeding. 


Sometimes mouth ulcers get infected. Infection is more serious when you’re having cancer treatment and your doctor will need to treat the infection quickly.

Continue your regular mouth care if you do develop an infection. Use all the medicines your doctor has given you, such as mouthwashes and lozenges.

A common infection of the mouth is thrush. Thrush causes white patches in your mouth. The skin inside your mouth can be very red and sore.

Treatment for sore mouths and thrush infections

You can usually treat thrush with anti fungal mouth drops, pastilles or a gel. You may also have a course of anti fungal tablets. You might need to have anti fungal treatment through a drip into a vein in your arm if the thrush is bad. 

Here are some tips to help relieve a sore or infected mouth. 

  • Brush your teeth regularly with a soft toothbrush and use an alcohol free mouthwash. Some people like to use a baby's toothbrush.

  • Clean your teeth with a foam mouth care stick or a piece of gauze dipped in mouthwash if your mouth is too sore for a toothbrush. Do ask your healthcare team if you are unsure what products or equipment to use.

  • With sores in your mouth that are crusty, rinse with mouthwash several times a day to loosen the crusts

  • Salt water rinses or bicarbonate of soda mouth rinses can help to keep your mouth clean.

  • You could try a gel mouthwash that sticks to the inside of your mouth and reduces pain from mouth ulcers

  • Choose bland, soft foods such as mashed potato, well cooked rice or scrambled eggs if they are easier to eat.

  • Don't eat spicy or salty foods, dry or crisp foods, citrus fruits or juices, these could irritate your mouth.

  • It is important to drink plenty of liquids.

  • It’s much better to take painkillers and be able to eat and drink, than to try to carry on without painkillers.

Dry mouth

A dry mouth is called xerostomia (pronounced zero-stow-mee-a) and there are several causes for it:

  • radiotherapy to the head and neck can affect your salivary glands, reducing the spit (saliva) in your mouth

  • side effects of some drugs, such as some painkillers, anti depressants and anti sickness medicines

  • breathing through your mouth

  • not eating or drinking enough

  • dehydration – this means that you don’t have enough fluid in your body and your skin, nose and mouth can also be very dry

Treatment for a dry mouth

Regular mouth care can prevent a dry mouth in some people. But sometimes problems can still happen. You can do several things to help with a dry mouth. Some of the following tips might help.

  • Sip drinks often to keep your mouth moist.

  • Suck on ice cubes, ice lollies or sugar free sweets.

  • Moisten your food with sauces, gravy, cream, custard or ice cream.

  • Chewing sugarless gum can make your salivary glands produce more saliva.

  • Use lip balm to keep your lips moisturised.

  • Use a soft toothbrush to clean your teeth and tongue, use moistened cotton wool if you can’t use a toothbrush for some reason.

  • Ask your doctor about gels or lozenges that stimulate saliva and artificial sprays.

Taste changes

Radiotherapy to the head and neck area and some cancer drugs may affect your taste buds. So your sense of taste might change as soon as you start treatment, or some time afterwards.

You might notice changes in the way your food tastes. Some people say their food has a metallic, bitter or salty taste. Others say that all foods taste the same. Taste changes are often temporary with chemotherapy or targeted cancer drugs.

Radiotherapy to some parts of the head and neck can cause long term side effects. These can sometimes be permanent. Before you start your treatment, ask your doctor if it’s likely to affect your taste.

It might help to avoid some of the foods that taste strange. Or you could deliberately choose foods with stronger flavours if everything tastes the same.

Dietitians can give you advice on dealing with taste changes. Ask your doctor or nurse to refer you.

Tooth and denture problems

Having radiotherapy to your mouth means you can be more at risk of getting tooth decay. So your radiotherapy specialist may arrange a dental appointment for you before you have this treatment. This may mean your dentist might need to remove any unhealthy teeth before you start.

Do make sure you go for your regular check ups after your course of treatment. And remember that if you’ve been having cancer treatment or are going to have it, tell your dentist before you have any dental work done.

Having fluoride treatment before your radiotherapy starts might help to protect your teeth. The fluoride treatment may be a mouthwash or gel you use every day.

If you have a sore and dry mouth it can make it difficult to wear dentures. You might be tempted to leave them out for long periods if they’re giving you a lot of trouble. But this isn’t usually a good idea as your gums can change shape so your dentures no longer fit.

Clean your dentures at least twice a day and ask your doctor or dentist for advice.

Stiff jaw

Certain muscles in your face help to move your jaw. The muscles can become stiff during radiotherapy or surgery to the head and neck area. This is called trismus.

Your doctor or dentist may suggest some gentle jaw exercises to help prevent this becoming a permanent problem.

Talking to a physiotherapist or a speech and language therapist at the hospital may help if you’re concerned. Ask your doctor, radiographer or nurse to refer you.

Bad breath

Bad breath is called halitosis. Most people have bad breath at some time or other. But cancer and treatment might make it worse.

It might help to clean your teeth or dentures regularly. And you can use alcohol free mouthwashes after cleaning or eating.

Loss of appetite due to mouth problems

You can lose your appetite if you have mouth problems, so you might lose weight. For example, if you are in pain or find it difficult to swallow you might not feel like eating or drinking.

Talk to your radiographer, doctor or nurse if you’re having problems.

The hospital team can prescribe painkillers if needed to help you get through this difficult time. They might also refer you to a dietitian for advice.

You can take food supplements, such as high calorie drinks, until your mouth feels better. Your doctor can prescribe these for you too. You may lose weight even if you take these supplements. So do tell your healthcare team if this is the case.

Occasionally doctors and dietitians suggest tube feeding if your mouth is very sore and you can't eat. You have this until your mouth recovers. You might have liquid food through a drip into your vein. Or you might have liquid food through a tube into your stomach. You might have to go into hospital to have the tube feeds, at least to start with.

Increase in saliva

This is sometimes called excessive salivation. It isn't a very common problem. But it can be uncomfortable and some people find it embarrassing.

The causes can include:

  • a painful mouth

  • drug side effects

  • mouth cancer

  • surgery to remove the jaw bone

  • swallowing difficulties

  • a change in your saliva after radiotherapy

Treatment for an increase in saliva

Having too much saliva can be even harder to cope with if you have difficulty swallowing. Your doctor might refer you to a speech and language therapist if you have swallowing difficulties.

Your doctor can also review the drugs you are taking. They might be able to prescribe a drug to reduce how much saliva you make.

Damage to the jawbone

Damage to the jawbone caused by cancer treatments is called osteonecrosis. This is a rare condition. The exact causes are not known. It can happen when you have one of the following treatments

  • bisphosphonates

  • denosumab

  • radiotherapy to the head and neck

Your doctor will tell you to see your dentist before starting treatment if your cancer treatment might cause jawbone damage. Treatment for a damaged jaw depends on:

  • how big the area of damage is

  • the amount of damage to the bone

You might have an antibiotic mouthwash, such as chlorhexidine, if the affected area is small and the damage isn’t very much. You might also have to take antibiotic tablets.

Your doctor will refer you to a specialist surgeon if necessary. Some people have surgery to remove the surrounding gum tissue to relieve symptoms. If there is a lot of damage your surgeon might need to remove part of your jaw.

  • Oral Care guidance and support in cancer and palliative care. Third Edition
    UK Oral Management in Cancer Care Group, June 2019

  • Palliative care - oral Clinical Knowledge Summaries​ 
    National Institute for Health and Care Excellence (NICE), revised July 2023

  • MASCC/ISOO Clinical Practice Guidelines for the Management of Mucositis Secondary to Cancer Therapy
    S Elad and others
    Cancer, 2020

  • Medication-related osteonecrosis of the jaw: Prevention, diagnosis and management in patients with cancer and bone metastases
    S Otto and others
    Cancer Treatment Reviews, 2018. Volume 69, Pages 177-187

  • Assessing taste and smell alterations in cancer patients undergoing chemotherapy according to treatment.​
    J Amézaga and others
    Supportive care in cancer, 2018

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. Please contact with details of the particular issue you are interested in if you need additional references for this information.

Last reviewed: 
22 Apr 2024
Next review due: 
22 Apr 2027

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