Mouth Sores from Cancer Treatment: What to Know and How to Cope

Mouth sores during cancer treatment (oral mucositis)

Mouth sores are a common side effect of cancer therapy. They can make eating, drinking, and talking uncomfortable. The medical term is oral mucositis. Your oncology team has ways to help. Learning what to expect and how to care for your mouth can make this side effect easier to manage.

Why might I get mouth sores?

Chemotherapy can injure the fast-growing cells that line your mouth. Radiation to the head or neck can also irritate mouth tissues. Not everyone gets mouth sores. Your risk depends on the medicines, doses, and your overall health.

With chemotherapy, sores often begin a few days after treatment and peak around the first week.
With head and neck radiation, sores usually start within 2–3 weeks and build during treatment.
Dry mouth, dental problems, or infections can also play a role. Your team can check the cause.

If you have had mouth sores before, tell your care team before your next cycle so you can plan ahead together.

What do mouth sores feel like?

Symptoms can be mild or severe, and may affect your lips, tongue, cheeks, gums, and throat.

Red, swollen, or shiny areas; burning or tingling
White patches that can turn into open sores
Pain with chewing or swallowing; sore throat
Dry mouth, taste changes, or bad breath

Severe mouth sores can make it hard to eat or drink. If this happens, contact your care team promptly.

Can mouth sores be prevented?

Some steps may lower your chance of getting mouth sores. Talk with your oncology team before starting any new routine.

Get a dental checkup before treatment if possible. Treating cavities or gum disease first may help.
Ask whether using ice chips during certain chemotherapy infusions (sometimes called cryotherapy) is appropriate for you.
Use a bland baking soda mouth rinse as a preventive mouthwash, starting on day one of treatment, if your team agrees. Mix 1/2 teaspoon of baking soda in 1 cup (8 oz) of warm water. Swish gently for 30 seconds and spit. Repeat several times a day, especially after meals and at bedtime. Do not swallow. If salt does not sting, you may add a small pinch, but baking soda alone is fine.
Begin gentle daily mouth care early and keep it going every day.

These steps can help keep your mouth clean, neutralize acids, and reduce irritation.

What can you do on your own?

Gentle mouth care and smart food choices can ease symptoms and support healing. Check any new steps with your team.

Rinse often: use the baking soda mouth rinse after meals and before bed. Avoid alcohol-based mouthwashes, peroxide, or iodine unless your team advises them.
Brush gently twice a day with a soft toothbrush. Use a small amount of mild toothpaste. If brushing hurts, ask about foam swabs.
Floss gently once a day if your team says it is safe. Stop if you see bleeding that doesn’t stop.
If you wear dentures, remove and clean them often. Limit wear time if your gums are sore.
Keep lips moist with a plain, non-irritating balm. Avoid tobacco products.
Choose soft, moist, cool, or room-temperature foods: yogurt, smoothies, oatmeal, eggs, mashed potatoes, soups, and well-cooked pasta.
Avoid spicy, acidic, salty, rough, or dry foods (chips, crusty bread), and very hot drinks. Limit caffeine and alcohol.
Stay hydrated with small, frequent sips of water or other gentle fluids. If eating is hard, ask your team about high-calorie, high-protein drinks and a dietitian referral.

What other treatments can help?

Your clinician can suggest options based on your symptoms, medical history, and treatment plan.

Medicinal mouth rinses that numb and coat sores to ease pain before meals
Pain medicines taken by mouth when needed
Treatment for infections if they develop
Clinic-based options your center may offer for prevention or symptom relief

If you cannot eat or drink enough because of mouth pain, short-term IV fluids or nutrition may be used until your mouth heals. Ask your team what is right for you.

When will my mouth sores get better?

With chemotherapy, sores usually improve within several days and often heal before the next cycle. They may return depending on the drug and dose.
With head and neck radiation, sores often build week by week. Healing usually begins a few days after radiation ends and continues over weeks.

Healing time varies. Gentle mouth care, rest, and good nutrition support recovery.