While you’re receiving treatment for cancer, some of the drugs you take can cause painful sores to develop inside your mouth. You can also get them if you’ve had a bone marrow (stem cell) transplant as part of your cancer care.

Although they often heal on their own, these mouth sores can make it uncomfortable to eat and talk. We’ll discuss what you can do to relieve the pain and prevent them from getting worse.

Mouth sores can be a common side effect of cancer treatment. The condition, known as stomatitis or mucositis, is an inflammation of the tissues inside your mouth.

Whitish, ulcer-like sores can form on your cheeks, gums, lips, tongue, or on the roof or floor of your mouth. Even if you don’t develop mouth ulcers, you may have patches that feel inflamed and painful, as if they’ve been burned.

Anyone who is receiving chemotherapy, radiation therapy, or a bone marrow (stem cell) transplant can develop mouth sores as a side effect of these treatments.

If you have dry mouth or gum disease, or if your teeth and gums are not well taken care of, you may be at a higher risk of getting mouth sores during your treatment. Women and people who smoke or drink alcohol are also at a higher risk, according to the Oral Cancer Foundation.

If you’re receiving chemotherapy, the sores could begin forming anywhere from 5 days to 2 weeks after your treatment. Depending on the specific cause, the sores could go away on their own in a few weeks, or they could last longer.

It’s important to find ways to manage your pain and to watch for signs of an infection. Cancer-related mouth sores can lead to weight loss, dehydration, and other serious complications.

You may notice symptoms anywhere between a few days and a few weeks after your cancer treatment. Here’s what you may see and feel as mucositis develops:

  • red or white patches
  • open sores (like ulcers or canker sores)
  • pain
  • swelling
  • bleeding
  • sore throat
  • difficulty eating, drinking, or swallowing
  • necrosis (“dead” tissue)

You may notice that the sores become slightly crusty as they heal. It’s important to keep track of your symptoms and let your oncologist know if the sores aren’t healing on their own.

Contact a doctor right away if you:

  • develop a fever
  • begin to lose weight because you can’t eat or drink properly
  • your sores worsen or become more painful

Untreated mouth sores can lead to malnutrition, dehydration, and life-threatening infections.

How long do mouth sores last?

The length of time your mouth sores may last depends on the specific cancer treatment you’ve had. Here are some estimates broken down by treatment:

  • Chemotherapy. If you have sores following chemotherapy, they will probably heal within 2 to 4 weeks, as long as an infection doesn’t develop.
  • Radiation therapy. If your sores are related to radiation therapy, the healing process can take a little longer — generally 6 to 8 weeks.
  • Chemoradiation. If you have had chemoradiation with a stem cell transplant, sores may go away in as little as 2 weeks.
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There are a few different ways that you can help mouth sores heal and avoid prolonger pain or an infection.

Good dental hygiene

While the sores are healing, it’s very important to keep the inside of your mouth clean to prevent an infection from developing.

The National Cancer Institute recommends that you gently clean your teeth every 4 hours and just before you go to sleep at night. Here are a few tips to consider:

  • Use a toothbrush with very soft bristles to clean your teeth. You can soften bristles by running your toothbrush under hot water.
  • Rinse with a mild mouthwash that doesn’t contain alcohol. Rinsing with plain water is fine.
  • If the sores get crusty, you can rinse with a solution made with equal parts water or saltwater and 3 percent hydrogen peroxide. Limit this treatment to only 2 days, as it can slow the healing of the sores if used longer.
  • Keep up with a gentle daily flossing routine.
  • To reduce pain, dab a topical oral pain medication like benzocaine (Orajel) onto affected areas.

Regular rinses

If the pain from mouth sores is interfering with your ability to eat and drink, a doctor may treat the condition with a opioid mouthwash or one containing doxepin or lidocaine.

To ease discomfort and keep your mouth from feeling dry, you may want to try rinsing with a mild saltwater or baking soda solution. Here’s how to make each of them:

  • Saltwater solution. Stir 1 teaspoon (5 grams) salt into 4 cups (1 liters) of water until dissolved.
  • Baking soda solution. Add 1 teaspoon (5 grams) baking soda to 8 ounces (240 milliliters) of water and mix thoroughly.

Your cancer care team may recommend that you use a lubricating liquid (artificial saliva) to moisten the inside of your mouth if dryness is a problem. These liquids are usually gel-like. They coat your mouth with a thin film to help ease discomfort and promote healing.

Some people have found it useful to rinse with a blend of medications called the magic mouthwash. Formulas for this mouthwash vary, but most of them include a combination of medications to treat different symptoms, including:

  • antihistamines
  • corticosteroids
  • antifungals
  • anesthetics
  • antacids
  • antibiotics

Magic or miracle mouthwash solutions usually have to be prescribed by a doctor and prepared by a pharmacist, although some people mix up an over-the-counter version at home.

There isn’t enough research to say for sure whether magic mouthwash works. If you think you’d like to try it, talk with your oncologist or a healthcare professional about whether it’s a good idea for you.

More tips for dealing with mouth sores

Here are a few more things you can try at home that may help ease pain from mouth sores:

  • Chew ice chips to help numb painful areas.
  • Stop smoking or using tobacco products.
  • Dab on an over-the-counter oral pain medication to ease discomfort.
  • Limit or avoid spicy, salty, and acidic foods.
  • Choose soft foods that don’t require you to chew a lot.
  • Make sure your food is not too hot or too cold.
  • Pass up foods with sharp edges, such as chips, that could be painful to eat.
  • Rinse your mouth often with cool water, a medicated rinse, saltwater, or baking soda solutions.
  • Take care of your teeth and gums with good dental hygiene practices.
  • Eat fruits, vegetables, and high-quality proteins to promote your overall health.
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Cancer cells can grow very quickly. The aim of cancer treatment is to stop or slow down that growth. The cells in the mucous membranes lining your mouth are also fast-growing cells, so cancer treatments affect them, too.

Cancer treatments also keep the cells in your mouth from being able to repair themselves efficiently when they’re damaged.

Dry mouth

Radiation therapy can also damage the glands in your mouth that make saliva. A dry mouth is more susceptible to infections that cause mouth sores.


Chemotherapy and radiation can both change the microbiome in your mouth, upsetting the balance between good and bad bacteria. The growth of harmful bacteria in your mouth can also lead to mouth sores.

Sometimes cancer treatments suppress your immune system, which may make it more likely that you’ll get a bacterial, viral, or fungal infection that causes mouth sores. An older infection (such as the herpes simplex virus) can also suddenly flare up again.

Graft-versus-host disease

If you’ve had a bone marrow (stem cell) transplant, sores may be a sign that you’ve developed a condition known as graft-versus-host disease (GVHD).

When this happens, the cells in your body are attacking the transplanted cells as though they were an unhealthy invader. According to research published in Journal of Clinical and Experimental Dentistry, short-term (acute) GVHD occurs in 50 to 70 percent of stem cell transplant cases and longer-term (chronic) GVHD is seen in 30 to 50 percent of cases.

The form of GVHD that causes mouth sores is usually mild, and doctors often treat it with corticosteroid medications.

It’s important to talk with a doctor if you develop mouth sores after a stem cell transplant, as some kinds of GVHD can turn serious if left untreated.

There is a good chance that you’ll experience mouth sores at some point during your cancer treatment. Researchers estimate that 20 to 40 percent of those who have chemotherapy and 80 percent of those who have high-dose chemotherapy will develop mucositis afterward.

Still, there are steps you and your cancer care team can take to lower your risk, reduce the severity of the sores, and promote faster healing.

Preventative dental care

About a month before your cancer treatment begins, schedule an appointment with a dentist to make sure your teeth and gums are healthy. If you have cavities, broken teeth, or gum disease, it’s important to come up with a dental treatment plan to take care of these conditions so they don’t lead to infections later, when your immune system may be vulnerable.

If you wear braces or dentures, ask a dentist to check the fit and remove any part of the device you don’t need during your treatment.

It’s very important to maintain good oral hygiene practices throughout your treatment to lower your risk of infection. Brush and floss gently but regularly, avoiding any painful areas. You can also ask a dentist whether a mouth rinse with fluoride is advisable in your case.

Preventative treatments


For certain kinds of chemotherapy (bolus 5‐fluorouracil chemotherapy and some high-dose therapies), your healthcare team may give you ice chips to chew for 30 minutes before your treatment. This type of cold therapy can lower your risk of getting mouth sores later.


During treatment of some blood cancers, doctors may give you injections of palifermin, also known as human keratinocyte growth factor-1 (KGF-1), to prevent mouth sores.

Low-level laser therapy

If you’re scheduled to receive high-dose chemotherapy or radiotherapy, your cancer care team may prepare your mouth using low-level laser therapy beforehand to keep you from getting mouth sores.

Benzydamine mouthwash

For people who have radiation therapy for head and neck cancers, doctors may prescribe this medicated mouthwash to minimize mouth sores.

Mouth sores are one of the most common side effects of cancer treatment. Shortly after chemotherapy, radiation, or transplant treatments, painful, ulcer-like sores can form on the inside of your mouth.

These sores may go away on their own. If they don’t, it’s important to seek medical treatment for them because they can lead to very serious complications.

Before you start cancer treatments, visit a dentist to make sure your teeth and gums are healthy. Keeping up good dental hygiene practices during and after cancer treatment will help limit mouth sores.

If the sores are keeping you from eating and drinking, talk with your oncologist about medications could relieve the pain and speed up the healing process, so you can enjoy a better quality of life during treatment.

It’s really important to keep track of any sores in your mouth so you can reach out to your healthcare team if they don’t improve. Sores that deepen or worsen can lead to serious — even life-threatening — complications.