Mouth sores caused by cancer treatment: How to cope

Date Updated: 08/30/2022

If you're about to start cancer treatment, know that certain treatments can cause mouth sores. The term that health care providers use for mouth sores is oral mucositis.

Mouth sores can hurt and feel uncomfortable. They can range from minor problems to severe complications. They could make you stop your cancer treatment. These sores can make it hard to drink and could make you lose weight because you can't eat enough.

What are cancer-related mouth sores?

Cancer-related mouth sores form on the inside of your mouth or on your lips. The sores look like burns and can hurt. Mouth sores can make it hard to eat, talk, swallow and breathe.

Sores can happen anywhere on the soft tissues of your lips or your mouth. Sores can happen on the gums, the inside of your cheeks, tongue, and roof or floor of the mouth. Sores can also happen in the tube that carries the food you swallow to your stomach. This tube is called the esophagus.

Which cancer treatments cause mouth sores?

In general, cancer treatments that can cause mouth sores include:

Chemotherapy
Radiation therapy aimed at the head and neck
Bone marrow transplant, also known as a stem cell transplant
Targeted therapy
Immunotherapy

Whether your cancer treatment will cause mouth sores depends on which treatments you have and what doses you receive. Ask your health care provider whether your specific medicines or treatments might cause mouth sores.

What can I do to prevent mouth sores?

Although there's no sure way to prevent mouth sores, you can lower your risk. Talk to your health care provider about your risk of mouth sores and what you can do.

Your provider might recommend that you:

Get a dental checkup. Visit your dentist before you begin cancer treatment. Make sure to take care of any current issues with your mouth. These can include gum disease, cavities or teeth that need to be pulled. Any pain or infections in your mouth will get worse after you begin treatment. Continue regular dental checkups during treatment, especially if you have mouth sores.
Tell your provider if you have a history of mouth sores. If you've had mouth sores in the past, tell your provider. For example, tell your provider if you've had mouth sores caused by herpes simplex virus. Your provider might recommend medicine to prevent those types of mouth sores from happening during cancer treatment.
Take care of your teeth. Brush your teeth and rinse your mouth several times a day. Check the labels on mouthwashes and don't use alcohol-based products.

Floss every day, especially after eating. Develop a routine for your mouth care now. That will make it easier to continue during your treatment.
Stop smoking. If you smoke, quit. Smoking during treatment will make it harder for your mouth to heal itself.
Eat a diet with lots of fruits and vegetables. Choose a diet that includes plenty of fruits and vegetables. You'll need the vitamins and nutrients they provide to help your body fight infections during treatment.

Your provider may recommend other ways to reduce your risk of mouth sores, such as:

Using ice or water to keep your mouth cold. During certain types of chemotherapy treatment, it might help to swish ice chips or cold water around in your mouth. The cold limits the amount of treatment that reaches your mouth. This can lower your risk of mouth sores.
Medicine. Medicines to lower the risk of mouth sores might be an option for people having certain cancer treatments. These medicines might help those having bone marrow transplants or certain targeted therapy treatments.

How are mouth sores treated?

Even if you try to prevent mouth sores, you may still get them. Treatment for mouth sores can help control the pain as you wait for the cells in your mouth to heal.

Tell your health care provider if your mouth feels sensitive or you notice any sores forming. Your provider may recommend treatments, such as:

Coating agents. These medicines coat the inside of your mouth. They form a film to protect the sores and minimize the pain you might feel while eating or drinking. Your provider may tell you to swish and spit the medication.
Topical painkillers. These gel-like medicines can be put directly on the mouth sores. Your mouth may feel numb when using painkillers. Take care when eating or brushing your teeth because you won't be able to feel if you're hurting your mouth more.

There are other simple steps you can take to lower the pain of mouth sores. You might:

Avoid painful foods. Stay away from acidic foods and spicy foods. These could make your mouth feel worse. Don't eat sharp and crunchy foods. These include chips, crackers and pretzels. Instead choose soft foods and cut them in small pieces.

Alcohol also can hurt an already sore mouth. Don't drink alcohol or use alcohol-based mouthwash. Read the labels carefully.

Eat foods at room temperature or slightly warm. Hot or cold foods might be painful to eat.
Eat small meals more frequently. Cut your food into small pieces and eat slowly.
Use a straw. Use a straw for drinking to keep liquids away from the sore parts of your mouth.
Continue cleaning your mouth. It may hurt too much to use a toothbrush. Ask your health care team or your dentist about special foam swabs. They may be easier on your gums.

Rinse out your mouth several times a day. Avoid mouthwashes that contain alcohol.
Mix water with a little salt to swish around in your mouth. You could also try a combination of baking soda and warm water.

What happens if mouth sores become severe?

If your mouth sores get worse, they can become severe and cause other problems. Sometimes these problems get so bad that you have to stop your cancer treatment for a while.

Complications can include:

Infection. Mouth sores offer an easy way for germs to get into your body. Cancer treatment can weaken your immune system and serious infections can happen. Continue cleaning your teeth and mouth during and after treatment to lower your risk of infection.
Bleeding. Chemotherapy reduces your body's ability to stop bleeding if it starts. Mild bleeding from your mouth might cause some spotting when you brush your teeth. Sometimes bleeding is severe and can be difficult to stop.

When your mouth sores bleed, continue cleaning your mouth as best you can. That may mean just rinsing with water.
Problems eating and swallowing. Painful mouth sores can make it hard to eat and drink. If you're quickly losing weight, your health care provider may recommend a feeding tube to get you the nutrients you need.