If you're about to begin cancer treatment, be aware that certain treatments can cause mouth sores (oral mucositis). Mouth sores can be painful and distressing. They can range from an inconvenience to a severe complication that may make you unable to continue your cancer treatment.

As you begin your cancer treatment, understand how your treatment can cause mouth sores and what steps you can take to help prevent this complication. If you're already experiencing mouth sores, find out what you and your doctor can do to minimize the pain. Understanding how to manage any side effects you experience can make you feel more in control of your body as you go through cancer treatment.

Cancer-related mouth sores are red sores or ulcers that form on the lining of the inside of your mouth (mucous membranes) or on your lips. The sores appear burn-like and can be painful, making it difficult to eat, talk, swallow and breathe. Sores can appear on any of the soft tissues of your lips or your mouth, including your gums, your tongue or the roof and floor of your mouth.

Chemotherapy and head or neck radiation can both cause mouth sores during cancer treatment. That's because these treatments are intended to stop rapidly growing cells — such as cancer cells. Some healthy cells in your body also divide and grow rapidly, including the cells that line the inside of your mouth. Unfortunately these healthy cells are also damaged by chemotherapy and radiation. Damage to the cells in your mouth makes it difficult for your mouth to heal itself and to fend off bacteria, leading to sores and infections.

Bone marrow or stem cell transplants also can lead to mouth sores if you develop graft-versus-host disease (GVHD). In GVHD the transplanted cells or stem cells try to reject your body's normal cells. The transplanted cells view your body's cells as foreign and attack them. Mouth sores are just one sign of GVHD.

Whether or not you experience mouth sores during cancer treatment depends on a number of factors, including your individual treatment. Some people are more likely to develop mouth sores, including:

• Younger people
• People with pre-existing gum disease
• People who don't brush and floss regularly
• People taking certain medications, including certain medications for depression and certain pain medications

People who receive both chemotherapy and head or neck radiation are most likely to experience mouth sores.

Here's what you can expect with each type of cancer treatment:

Chemotherapy
Whether you experience mouth sores while undergoing chemotherapy depends on the type and dose of medication you receive, as well as how often you receive your treatment. The chemotherapy drugs most likely to cause mouth sores include:

• Cytarabine (Cytosar-U)
• Doxorubicin (Adriamycin, Rubex)
• Etoposide (Etopophos, Toposar, Vepesid)
• Fluorouracil (Adrucil)
• Methotrexate
• Capecitabine (Xeloda)

Mouth sores usually develop a few days after treatment begins and go away 10 to 14 days after treatment ends. Sores may begin as mild pain or burning in your mouth. White patches may form on the gums and soft tissues in your mouth. As the sores grow and lose their covering, they become large red lesions. The mouth sores usually reach their peak around the seventh day of chemotherapy treatment. In severe cases, mouth sores can bleed or cause extreme pain that makes it impossible to eat, drink or speak.

Head or neck radiation therapy
Only radiation aimed at your head or neck causes mouth sores. Whether or not your radiation treatment will cause mouth sores depends on how much radiation you'll receive. Unlike with chemotherapy, mouth sores caused by radiation usually develop later in your treatment and can last longer after treatment ends. You may begin to experience mouth pain two to three weeks after you begin radiation. Patchy lesions may develop in your mouth in the following weeks. More intense doses of radiation will cause mouth sores to develop more quickly. Mouth sores from radiation usually last six to eight weeks.

Bone marrow or stem cell transplant
Mouth sores associated with GVHD develop two to three weeks after a bone marrow or stem cell transplant. People who receive transplants usually receive high-dose chemotherapy or radiation to prepare their bodies for the transplant. Since these therapies also cause mouth sores, it can be difficult to tell whether the sores are from treatment or GVHD. Your doctor may test cells from your mouth to determine what's causing your mouth sores.

No guaranteed way to prevent mouth sores exists. But there are many ways to reduce your risk of developing them. Talk to your doctor about your risk of developing mouth sores and whether you should try preventive measures. Your doctor might recommend that you:

• Get a dental checkup. Visit your dentist before you begin treatment to take care of any unresolved dental issues, such as gum disease, cavities or teeth that need to be pulled. Any pain or infections in your mouth will only worsen once you begin treatment.
• Take care of your teeth. Get in the habit of brushing your teeth and rinsing your mouth several times a day. Floss every day, especially after eating. Developing a routine for your mouth care now will make it easier to continue throughout your treatment.
• Stop smoking. Smoking during treatment will only make it harder for your mouth to heal itself.
• Eat a well-balanced diet. Vary your diet to include plenty of fruits and vegetables. You'll need the vitamins and nutrients they provide to help your body fight infections during treatment.
• Drink plenty of water. Drink 2 to 3 quarts of water every day. Keeping hydrated enhances your overall well-being and keeps your body running smoothly as you prepare for treatment.

Depending on your cancer and your treatment, your doctor may recommend other techniques for reducing your risk of mouth sores, such as:

• Cold therapy (cryotherapy). If you're receiving fluorouracil, sometimes called 5-FU, as part of your chemotherapy treatment, it might help to swish ice chips around in your mouth for the first half-hour of your treatments. The cold limits the amount of the drug that reaches your mouth, reducing your risk of mouth sores.
• Medication to repair mouth cells. Palifermin (Kepivance) stimulates the growth of cells on the surface of your mouth. If the cells of your mouth recover quickly, you're less likely to experience severe mouth sores. Palifermin is only approved in people with leukemia and lymphoma who receive bone marrow transplants. However, it's being tested in people with other types of cancer.
• Low-energy laser therapy. Exposing your mouth to laser energy can stimulate cell growth after high doses of chemotherapy and during and after radiation therapy. Laser therapy requires expensive equipment and specialized training, so it isn't available everywhere. It may only be available at specialized cancer centers.

Despite efforts to prevent mouth sores, you can still develop this treatment side effect. Treating mouth sores primarily involves minimizing your pain until the cells of your mouth heal and begin regenerating after your treatment ends.

Tell your doctor if you develop any sensitivity in your mouth or notice any sores forming. Your doctor may recommend treatments, such as:

• Coating agents. These medications coat the entire lining of your mouth, forming a film to protect the sores and minimize the pain you might feel while eating or drinking.
• Topical painkillers. These medications can be applied directly to your mouth sores. Your mouth may feel numb when using painkillers, so be careful when eating or brushing your teeth because you won't be able to feel if you're causing more injury to your mouth.

In addition to medications, you can take simple steps to reduce the pain you feel from mouth sores. You might:

• Avoid painful foods. Stay away from acidic foods and spicy foods that could further irritate your mouth. Avoid sharp and crunchy foods, such as chips, crackers and pretzels, and instead opt for softer foods cut in small pieces. Caffeine and alcohol also can irritate an already sore mouth. Eat foods at room temperature or slightly warm, since 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. A straw for drinking keeps liquids away from sore areas in your mouth.
• Continue cleaning your mouth. If it's too painful to use a toothbrush, ask your health care team or your dentist about special foam swabs, which are easier on your gums. Rinse out your mouth several times a day. Avoid mouthwashes that contain alcohol. Mix a weak saltwater solution to swish around in your mouth or use plain water.

If your mouth sores progress, they can become severe and cause other complications. Sometimes these complications become so severe that you have to stop your cancer treatment temporarily. Complications can include:

• Infection. Mouth sores offer a convenient way for germs and viruses to get into your body. Since cancer treatment can weaken your immune system, serious infection can result. Continue cleaning your teeth and mouth during and after treatment to reduce your risk of infection.
• Bleeding. Chemotherapy reduces your blood's ability to clot. Bleeding from your mouth can be mild, with some spotting when you brush your teeth, to severe, with bleeding that's difficult to stop. Your doctor will monitor your blood counts and give you medications to help your blood clot. When your mouth sores bleed, it's important to continue cleaning your mouth as best you can — even if that means just rinsing with water.
• Difficulty eating and swallowing. Painful mouth sores can make eating and drinking difficult. If eating small meals of soft foods isn't helping and you're quickly losing weight, your doctor may recommend a feeding tube to get you the nutrients you need to fuel your body.

Researchers are working to develop new ways to prevent mouth sores, to relieve pain and to prevent further complications. Until then, work with your health care team and your dentist to make sure your mouth is in good shape as you prepare for treatment. Though mouth sores can be distressing, know that they are temporary and the pain can be minimized.