The short answer
Thrush is an overgrowth of the fungus Candida in the mouth. Chemotherapy weakens the immune system, which is one of the situations that makes it more likely. It shows up as white velvety sores, and MedlinePlus says it can be cured with antifungal treatment.
MedlinePlus describes thrush as a yeast infection of the tongue and lining of the mouth caused by Candida overgrowth.
A weakened immune system, including from chemotherapy, is listed as a risk factor.
White velvety sores in the mouth or on the tongue are the classic sign.
Bleeding when brushing teeth and pain when swallowing are also listed symptoms.
On this page
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This page is for people getting chemotherapy who may have oral thrush, a yeast infection in the mouth. It covers warning signs, causes, how it is diagnosed and treated, and daily mouth care.
When to get help sooner
Call 911 if your throat swells so that breathing becomes difficult, or if you cannot swallow your own saliva.
Call your doctor or nurse immediately if you have a fever of 100.4 °F (38 °C) or higher while you are having chemotherapy. Fever during chemotherapy is a medical emergency in CDC's guidance. It says to call your doctor right away at that temperature, and to know which number to call when the office is closed. If you go to an emergency room, tell the person checking you in that you are a cancer patient getting chemotherapy.
Call your care team the same day if you have white sores in your mouth, difficulty swallowing, or pain in your mouth, lips or throat that makes it hard to eat, drink or sleep. MedlinePlus advises contacting your provider if you have thrush-like sores or trouble swallowing, especially during chemotherapy. NCI says to tell your team about mouth pain that makes it hard to eat, drink or sleep.
An infection in someone whose immune system is suppressed is not something to watch for a week.
What you are looking at
MedlinePlus describes thrush as a yeast infection of the tongue and lining of the mouth. It is caused by overgrowth of a fungus called Candida.
A weakened immune system, including from chemotherapy, makes it more likely.
The signs MedlinePlus lists are:
- White velvety sores in the mouth or on the tongue.
- Bleeding when you brush your teeth or scrape the sores.
- Pain when swallowing.
Why chemotherapy patients get it
MedlinePlus lists people with weakened immune systems, naming HIV and AIDS and chemotherapy, among those at higher risk.
The other risk factors are worth knowing. Several can add up during cancer care:
- Recent antibiotic use. Antibiotics kill the bacteria that normally keep fungus in check.
- Steroid medicines. These are part of many cancer regimens.
- Diabetes with high blood sugar.
- Ill-fitting dentures.
- Poor health generally, or advanced age.
If you have recently finished a course of antibiotics for another infection, and you are on steroids as part of your regimen, you have collected several of these at once. That is not bad luck or poor hygiene. The risks simply add up.
How it is confirmed
MedlinePlus says providers usually identify thrush through visual examination. Sometimes a sore is scraped so the cells can be looked at under a microscope. In severe cases, throat cultures may be taken.
This is one reason to have someone look at it rather than describe it over the phone.
Treatment
MedlinePlus separates mild from more serious cases.
For mild thrush it mentions yogurt or acidophilus pills. For moderate to severe cases it lists antifungal mouthwash, lozenges, or oral medicines such as fluconazole.
Ask your care team rather than buying something at the store. You are on cancer treatment, and drugs can interact. Is fluconazole right for you, and is it safe with everything else you are taking? That decision needs your medication list in front of someone qualified to read it.
The outlook
MedlinePlus states that oral thrush can be cured. That is reassuring, and worth holding onto when your mouth is sore and you are tired of setbacks.
It also says that if your immune system is weak, thrush may come back or cause more serious problems. If your immunity stays low through several more cycles, thrush may return. Knowing that in advance means you can catch it early the second time rather than spending a week wondering.
Daily habits that support your mouth
NCI's guidance for cancer treatment recommends checking your mouth every day for sores or white spots. This habit can help you catch thrush early.
It also recommends gently brushing with a very soft toothbrush after meals and at bedtime. It also suggests rinsing through the day with a warm water, baking soda and salt mixture. Gentle and frequent is the goal.
If you wear dentures, remember that MedlinePlus lists ill-fitting dentures as a risk factor. If yours have stopped fitting well, that is worth mentioning too.
Sources
Common questions
How is thrush diagnosed?
MedlinePlus says healthcare providers typically identify thrush by looking at it. Confirmation may involve scraping a sore to examine under a microscope, or throat cultures in severe cases.
What makes it more likely besides chemotherapy?
MedlinePlus lists HIV and AIDS, poor health or advanced age, diabetes with high blood sugar, recent antibiotic use because antibiotics kill protective bacteria, ill-fitting dentures, and steroid medicines.
Can I treat it myself?
MedlinePlus mentions yogurt or acidophilus pills for mild cases, and antifungal mouthwash, lozenges or oral medicine for moderate to severe cases. Because you are in cancer treatment, this should be your team's call rather than yours.
Will it keep coming back?
MedlinePlus states that oral thrush can be cured, but recurrence is possible in people who are immunocompromised. That is worth planning for rather than being surprised by.
Questions to ask your doctor
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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.
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Sources last checked: 2026-08-11 what this meansLast updated: 2026-09-29Next planned review: 2027-08-11
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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: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right 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.
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