The short answer
Mouth Sores can happen during cancer treatment for several reasons. Track timing and severity, use care-team-approved self-care, and contact the care team promptly for red flags such as trouble drinking, inability to eat, fever, white coating, bleeding, or pain that interferes with sleep.
Mouth Sores can happen during treatment and has more than one possible cause.
Tell the care team early so they can treat symptoms and protect the treatment plan.
Helpful self-care may include gentle mouth care, soft foods, avoiding alcohol-based rinses, and reporting pain early.
Urgent or same-day help may be needed for trouble drinking, inability to eat, bleeding, or pain that interferes with sleep. Fever, chills, or a white coating during chemotherapy needs a call right away, day or night.
Choose how you want to read this
The whole article, with every detail and caution.
This page is for people with mouth sores from cancer treatment. It covers why they happen, how to prevent and manage them, and when to get help.
Why mouth sores happen
Cancer treatment can injure the cells lining your mouth and throat. Radiation to the head and neck can harm the salivary glands and the tissue in your mouth. Chemotherapy and immunotherapy can injure fast-growing cells there too, including in your mouth, throat, and lips. Doctors call these sores and irritation mucositis (say: myoo-koh-SY-tis).
Getting ahead of it before treatment starts
See a dentist before treatment begins, if there is time. Finishing any needed dental work first lowers your risk of infection later. During treatment, check your mouth every day for sores, redness, or white patches. Rinse with a warm water, baking soda, and salt solution after meals, and use a very soft toothbrush.
Managing sores day to day
Choose soft, wet foods, and use sauces or broth to soften dry foods. Avoid crunchy, salty, spicy, or sugary foods, and skip alcohol and alcohol-based mouthwash. Cold foods, like a smoothie or ice chips, can be soothing for some people. Ask your team about numbing sprays or lozenges if pain makes eating hard.
Why fever with mouth sores is different
Mouth sores can become an entry point for infection, especially when your blood counts are low from treatment. A fever with mouth sores is not something to wait out.
When to get help sooner
- Call 911 or go to an emergency department if you cannot swallow your own saliva, or your mouth or throat swells enough to make breathing hard. Do not drive yourself.
- Call 911 or go to an emergency department if you cannot keep fluids down or cannot swallow enough to drink. Do not drive yourself.
- Ring your care team at once, at any hour, if your temperature reaches 100.4°F (38°C) or higher, or you feel chilled and shaky, during treatment. CDC's guidance is plain: fever during chemotherapy is a medical emergency. NCI says infections during treatment can be life threatening. If no one answers quickly, go to an emergency department and tell them you are in cancer treatment.
- Call your care team the same day if pain in your mouth, lips, or throat stops you from eating, drinking, or sleeping.
- Call your care team right away, day or night, if you see white patches or a white coating in your mouth, or a sore throat or chills, while you are having chemotherapy. These can be signs of infection, and a normal temperature is not a reason to wait.
- Call your care team the same day if your gums or sores bleed and the bleeding does not stop.
- Call your care team within a day or two if sores are slowly getting worse, or you are drinking less than usual.
Do not wait for your next scheduled visit for any of these.
What to ask your team
- Should I see a dentist before treatment starts?
- What rinse and mouth-care routine do you recommend for my treatment?
- What pain relief options are safe with my other medicines?
- What temperature or symptom means I should call immediately?
- Are there foods or products I should avoid completely during treatment?
Sources
- National Cancer Institute — Mouth and Throat Problems and Cancer Treatment
- National Cancer Institute — Oral Complications of Cancer Therapies (PDQ) Patient Version
- National Cancer Institute — Infection and Neutropenia during Cancer Treatment
- CDC — Watch Out for Fever (Preventing Infections in People With Cancer)
Common questions
Why can mouth sores happen during cancer treatment?
It can happen because of chemotherapy, radiation to the head and neck, targeted therapy, immunotherapy, infection, dry mouth, or low blood counts. Your team can help sort out the likely cause.
What should I track?
Track when it started, severity, triggers, medicines taken, related symptoms, and whether it is getting better or worse.
When should I call?
Ask your team for a personal call plan. Red flags include trouble drinking, inability to eat, fever, white coating, bleeding, or pain that interferes with sleep.
Questions to ask your doctor
Being prepared helps you get the most out of your appointments. Save or print these questions.
Tap a question to save it to your list (kept on this device).
Your next step
Write down timing, severity, triggers, and what helps.
Talk with a trained specialist or navigator
Cancer Explained provides educational guidance, but does not replace trained specialists, social workers, or your medical team.
Talk to a trained cancer information specialist
Free, confidential assistance from NCI Cancer Information Service via phone, chat, or email.
Contact your oncology team
Locate after-hours contact numbers, portal messages, or urgent triage phone lines.
Find a patient navigator
Get one-on-one help with appointments, logistics, translation, and care coordination.
Find a genetic counselor
Discuss inherited mutation risk, family history, and genetic testing options.
Find an oncology social worker
Access emotional counseling, family support groups, and mental health resources.
Find a financial navigator
Locate copay assistance foundations, grant programs, and lodging/travel support.
Find a clinical-trial specialist
Search matching studies and speak with NCI trial information specialists.
Get urgent help
Fever of 100.4°F (38°C) or higher during chemo, severe pain, or trouble breathing: call your cancer care team right away, day or night. Call 911 for an emergency.
Know someone who needs this?
Plenty of people are looking for something like this and do not know where to start. If this would help a friend or someone you love, send it on — we have written an opening line so you do not have to stare at an empty message. You can change every word of it.
Your message is written and sent in your own email or messaging app — we never see who you send it to, and nothing is added to any list.
Plain-language explanation of the published sources cited on this page. AI-assisted, source-checked, not clinician-reviewed.
Sources last checked: 2026-08-13 what this meansLast updated: 2026-09-30Next planned review: 2027-01-20
Review details and limits
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status — Editorial review complete. This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
General education — varies by person. Answers genuinely differ between people. This page explains what commonly varies and points you to your care team for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Words to know
Tap any term to see what it means.
Knowledge check
0 of 3 answered
This self-assessment checks understanding of educational content only. It is not medical advice.
How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Editorial review complete — This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Read more about our editorial process, our use of AI, and our corrections policy.
Spotted a problem? Report an error — a factual mistake, broken or outdated source, confusing wording, or anything that seems unsafe. Please do not include names, medical record numbers, dates of birth, addresses, or other identifying medical information in your report.
After using this page, do you understand what to do next?
Anonymous — we only record the answer, never who gave it.