Mouth Sores (Oral Mucositis)

Mouth sores, medically called oral mucositis, are a common and painful side effect of cancer treatment. They occur when chemotherapy or radiation damages the rapidly dividing cells lining the mouth and throat.

Medically reviewed by Dr. Sarah Chen, DDS, MD, Oral Medicine Specialist Last updated: January 2025

What is Oral Mucositis?

Oral mucositis is inflammation and ulceration of the mucous membranes lining the mouth and throat. It's one of the most debilitating side effects of cancer treatment, causing significant pain, difficulty eating and drinking, and reduced quality of life.

How Does It Develop?

The process occurs in five phases:

Initiation (Days 0-2): Chemotherapy or radiation damages DNA and generates free radicals
Upregulation (Days 2-3): Inflammatory signals are activated
Signal Amplification (Days 3-5): Inflammation cascade intensifies
Ulceration (Days 5-14): Visible sores develop as the mucosal lining breaks down
Healing (Days 14-21+): Tissue repair and regeneration occurs

Mucositis vs Stomatitis

Mucositis: Inflammation and ulceration specifically caused by chemotherapy or radiation
Stomatitis: General term for any inflammation of the mouth (includes mucositis, canker sores, infections)

In cancer care, these terms are often used interchangeably.

Impact on Treatment

Severe mucositis can lead to:

Treatment delays or dose reductions
Hospitalization for pain management and nutrition support
Increased risk of infection (especially with low white blood cells)
Reduced survival in some cancers if treatment is compromised

Causes and Risk Factors

Chemotherapy-Induced Mucositis

Certain chemotherapy drugs are more likely to cause mouth sores:

High-Risk Drugs (30-40% incidence)

5-Fluorouracil (5-FU): Especially with continuous infusion
Methotrexate: High-dose regimens
Cytarabine (Ara-C): High-dose
Doxorubicin: Particularly doxorubicin
Etoposide: Part of many regimens
Melphalan: High-dose for stem cell transplant

Moderate-Risk Drugs (10-30% incidence)

Docetaxel and paclitaxel: Taxanes - see paclitaxel
Irinotecan: Colorectal cancer treatment
Capecitabine (Xeloda): Oral 5-FU prodrug
Gemcitabine: Various cancers

Radiation-Induced Mucositis

Head and neck radiation: 80-100% develop mucositis
Severity increases with: Higher doses, larger treatment fields, concurrent chemotherapy
Timing: Usually begins week 2-3, peaks week 4-5, resolves 2-4 weeks after completion

Risk Factors

Patient Factors

Younger age: Children and young adults have faster cell turnover
Female gender: Unclear why, but consistently shown in studies
Poor oral hygiene: Pre-existing dental disease, gum disease
Poor nutritional status: Low albumin, vitamin deficiencies
Smoking and alcohol use: Irritate mucosa
Dehydration: Dry mouth increases risk

Treatment Factors

High-dose chemotherapy: Stem cell transplant conditioning
Continuous infusion: 5-FU given over days rather than bolus
Combination chemotherapy: Multiple mucositis-causing drugs
Concurrent chemoradiation: Synergistic effect
Neutropenia: Low white blood cells delay healing

Symptoms and Grading

Common Symptoms

Redness and swelling: Early sign before sores develop
Pain and burning: Can be severe, interfering with eating, drinking, talking
White or yellow patches: Areas of breakdown and ulceration
Open sores (ulcers): Visible breaks in the lining
Bleeding: Especially when brushing teeth or eating
Dry mouth: Reduced saliva production
Thick saliva or mucus: Difficulty swallowing
Difficulty swallowing (dysphagia): Pain with swallowing
Taste changes: Metallic or altered taste

WHO Mucositis Grading Scale

Healthcare providers use standardized grading to assess severity:

Grade	Description	Impact
Grade 0	No symptoms	Normal oral intake
Grade 1	Mild soreness, redness (erythema)	Can eat regular diet with minimal discomfort
Grade 2	Painful redness, ulcers; can eat solids	Can eat soft foods, needs pain medication
Grade 3	Painful ulcers; can only eat liquids	Liquid diet only, requires IV hydration often
Grade 4	Severe ulceration; cannot eat or drink	Requires IV nutrition (TPN) or feeding tube

Timeline

Chemotherapy: Usually appears 5-10 days after treatment, peaks at 7-14 days, resolves in 2-4 weeks
Radiation: Begins week 2-3 of treatment, worsens during treatment, peaks 1-2 weeks after completion, resolves 2-6 weeks later

Prevention Strategies

While mucositis cannot always be prevented, several strategies can reduce severity:

Baseline Oral Care

Before starting cancer treatment:

Dental evaluation: See dentist 2-4 weeks before treatment
Address dental problems: Treat cavities, gum disease, remove problematic teeth
Professional cleaning: Remove plaque and tartar
Establish baseline: Document existing oral conditions

Evidence-Based Prevention

Oral Cryotherapy (Ice Chips) - HIGHLY EFFECTIVE

For certain chemotherapy drugs only: 5-FU (bolus), melphalan, high-dose chemotherapy

Method: Suck on ice chips starting 5 minutes before chemotherapy and continuing for 30 minutes total
Mechanism: Cooling causes vasoconstriction (blood vessel narrowing), reducing drug delivery to mouth tissues
Effectiveness: Reduces mucositis incidence by ~40-50%
Not for all drugs: Doesn't work for continuous infusions or drugs with prolonged half-lives

Low-Level Laser Therapy (LLLT)

Evidence: Strong evidence for prevention in stem cell transplant and head/neck radiation
Method: Painless red or infrared laser applied to oral tissues
Availability: Limited to specialized centers
Mechanism: Stimulates cellular repair and reduces inflammation

Palifermin (Kepivance)

FDA approved for: High-dose chemotherapy before stem cell transplant
Mechanism: Growth factor that protects and heals mucosal cells
Dosing: 60 mcg/kg IV daily for 3 days before and 3 days after chemotherapy
Effectiveness: Reduces severe mucositis by ~40%
Cost: Very expensive, limited use

Good Oral Hygiene - ESSENTIAL

The single most important prevention strategy for all patients (see detailed protocol below).

Unproven or Ineffective Strategies

NOT recommended: Chlorhexidine mouthwash (no benefit shown, may worsen symptoms)
Insufficient evidence: Honey, glutamine, benzydamine, vitamin E, zinc

Oral Care Routine

Meticulous oral hygiene is the cornerstone of mucositis prevention and management.

Basic Oral Care Protocol

Brushing

Frequency: After every meal and at bedtime (minimum 4× daily)
Toothbrush: Extra-soft bristle brush
Toothpaste: Mild fluoride toothpaste (avoid strong flavors or whitening agents)
Technique: Gentle circular motions, brush for 2 minutes
Replace brush: Every 2-4 weeks or when bristles fray
If platelets low (<50,000): Use ultra-soft brush or foam swab to avoid bleeding

Rinsing

Frequency: Every 2-4 hours while awake and after eating
Solution: Baking soda rinse (1 teaspoon baking soda + 1 teaspoon salt in 1 quart warm water) OR plain saline (salt water)
Duration: Swish for 30-60 seconds, then spit out
AVOID: Alcohol-based mouthwashes (Listerine, Scope) - they are drying and irritating

Flossing

Continue daily if platelets >50,000 and gums not bleeding
Be gentle to avoid trauma
Stop if bleeding or platelets very low

Dentures

Clean daily with denture cleaner
Remove at night to allow tissues to rest
Ensure proper fit - poorly fitting dentures worsen mucositis
May need to avoid wearing if severe mucositis develops

Lip Care

Apply frequently: Petroleum jelly, lanolin, or water-based lip balm
Avoid: Flavored or medicated lip products that may be irritating
Keep lips moist to prevent cracking and bleeding

Hydration

Drink frequently: Sip water throughout the day
Goal: At least 8-10 cups of fluid daily (unless restricted)
Carry water bottle: Keep fluids readily available
Use humidifier: Especially at night to prevent dry mouth

Sample Daily Routine

Upon waking: Brush teeth, rinse with baking soda solution
After breakfast: Brush teeth, rinse
Mid-morning: Rinse with baking soda solution
After lunch: Brush teeth, rinse
Mid-afternoon: Rinse with baking soda solution
After dinner: Brush teeth, rinse
Before bed: Brush teeth, rinse, apply lip balm
Throughout day: Sip water frequently, apply lip balm as needed

Treatment Options

Once mucositis develops, treatment focuses on symptom management and supporting healing.

Pain Management

Pain control is critical for maintaining nutrition and quality of life.

Topical Pain Relief

Magic Mouthwash

A compounded prescription mouthwash with varying formulations. Common ingredients:

Viscous lidocaine 2%: Numbing agent (local anesthetic)
Diphenhydramine (Benadryl): Antihistamine with mild numbing effect
Maalox or Mylanta: Antacid to coat and soothe
Optional additions: Nystatin (antifungal), hydrocortisone (anti-inflammatory)

How to use: Swish 5-10 mL in mouth for 1-2 minutes, gargle, then spit out (or swallow if esophageal involvement). Use 15-30 minutes before meals and as needed for pain.

Note: Effectiveness varies. Some patients find it very helpful, others do not.

Systemic Pain Medication

For moderate to severe pain:

Acetaminophen (Tylenol): Mild pain, no anti-inflammatory effect
NSAIDs (ibuprofen): Use with caution if platelets low or bleeding risk
Opioids: Necessary for severe mucositis
- Morphine liquid (Roxanol) - swish and swallow before meals
- Oxycodone liquid or tablets
- Fentanyl patches for continuous pain control
- IV pain medication if unable to swallow

Patient-Controlled Analgesia (PCA)

For severe Grade 3-4 mucositis requiring hospitalization
IV morphine or hydromorphone with patient-controlled dosing
Allows better pain control and less anxiety

Infection Prevention and Treatment

Open sores provide entry for bacteria, viruses, and fungi.

Fungal Infections (Oral Thrush)

Signs: White coating on tongue, inner cheeks that doesn't scrape off easily
Prevention: Good oral hygiene, antifungal prophylaxis if high risk
Treatment: Nystatin swish-and-swallow, clotrimazole troches, fluconazole (Diflucan) oral or IV

Viral Infections (Herpes Simplex)

Signs: Painful blisters, often on lips or hard palate
Prevention: Acyclovir prophylaxis in high-risk patients (stem cell transplant)
Treatment: Acyclovir, valacyclovir, or famciclovir

Bacterial Infections

Signs: Increased pain, pus, fever
Risk: Higher with neutropenia (low white blood cells)
Treatment: Systemic antibiotics based on culture results

Bleeding Management

If bleeding: Apply gentle pressure with ice chips or gauze soaked in cold water
Tranexamic acid mouthwash: May help control bleeding in severe cases
Platelet transfusions: If platelets very low (<10,000-20,000)

Supportive Care

Saline irrigation: Gentle rinsing to keep mouth clean
Saliva substitutes: For dry mouth (Biotene, Salivart)
Growth factors: Palifermin (Kepivance) may be given therapeutically in severe cases (off-label)

When to Seek Medical Attention

Contact your healthcare team immediately if you experience:

Fever ≥100.4°F (38°C): May indicate infection
Severe pain: Not controlled with prescribed medications
Unable to eat or drink: Risk of dehydration and malnutrition
Difficulty swallowing: Even liquids
Excessive bleeding: From mouth sores
Signs of dehydration: Dizziness, dark urine, very dry mouth
White patches that don't rinse off: May be fungal infection

Eating and Drinking with Mouth Sores

Maintaining adequate nutrition is challenging but crucial during mucositis.

Foods to Choose

Soft, Bland Foods

Proteins: Scrambled eggs, cottage cheese, yogurt, smooth nut butters, protein shakes, tofu
Grains: Oatmeal, cream of wheat, mashed potatoes, white rice, pasta, soft breads (remove crusts)
Fruits: Bananas, applesauce, canned peaches/pears, melons, smoothies
Vegetables: Well-cooked and pureed or mashed (sweet potatoes, squash, carrots)
Liquids: Water, milk, milkshakes, cream soups, broth, herbal teas (room temperature or cool)

Helpful Techniques

Puree or blend: Use food processor or blender to make foods smoother
Add moisture: Gravies, sauces, butter, cream to make foods easier to swallow
Cool or room temperature: Hot foods increase pain
Small, frequent meals: 6-8 small meals rather than 3 large ones
Use straw: May help bypass painful areas (but not if mouth wide open hurts)
Numb before eating: Use magic mouthwash 15-30 minutes before meals

Foods and Drinks to Avoid

Acidic: Citrus fruits/juices, tomatoes, vinegar, pickles - burn sores
Spicy: Hot peppers, curry, hot sauce - increase pain
Salty: Chips, pretzels, salted nuts - irritating
Rough/scratchy: Crackers, toast, granola, raw vegetables - abrasive
Very hot: Hot beverages, soups - increase pain
Alcohol: Irritating and drying
Carbonated beverages: Can sting painful areas
Extremely sweet: Can be irritating

Hydration is Critical

Goal: 8-10 cups (64-80 oz) of fluid daily
Best choices: Water, diluted juice (non-acidic), milk, nutritional shakes
Sip frequently: Small amounts throughout the day
Ice chips: Soothing and hydrating
Popsicles: Frozen fruit juice bars (non-acidic)

Nutritional Supplements

High-calorie, high-protein shakes: Ensure, Boost, Carnation Instant Breakfast
Medical nutrition products: Specialized formulas (Ensure Plus, Boost Plus)
Add protein powder: To soups, smoothies, puddings
Consult dietitian: For personalized recommendations

When Oral Intake Becomes Impossible

For severe Grade 3-4 mucositis:

IV hydration: Prevents dehydration
Total Parenteral Nutrition (TPN): IV nutrition if unable to eat/drink for extended period
Feeding tube: Rarely needed for chemotherapy mucositis; more common with head/neck radiation (placed before treatment starts)

Sample Meal Plan for Severe Mucositis

Breakfast: Cream of wheat with butter and brown sugar, scrambled eggs (very soft), whole milk
Mid-morning: Protein shake (Ensure Plus)
Lunch: Cream soup (potato, butternut squash), soft white bread with butter, applesauce
Afternoon: Yogurt smoothie with banana
Dinner: Mashed potatoes with gravy, pureed chicken, cooked carrots (mashed)
Evening: Pudding or custard, whole milk
Throughout day: Water, ice chips, non-acidic juices (diluted)

Complications and Long-Term Effects

Potential Complications

Infection

Most serious complication, especially with neutropenia
Can lead to sepsis (life-threatening infection in bloodstream)
Requires hospitalization and IV antibiotics

Malnutrition and Dehydration

Inadequate oral intake due to pain
Weight loss, muscle wasting
Delayed healing, weakened immune system
May require hospitalization for IV fluids/nutrition

Treatment Interruption

Severe mucositis may require chemotherapy dose reduction or delay
Can impact cancer treatment outcomes
Radiation therapy generally continues but may need breaks

Chronic Pain

Severe mucositis can be extremely painful
May require strong opioid pain medications
Can affect quality of life significantly

Long-Term Effects

Most Mucositis is Temporary

Chemotherapy-induced: Heals completely within 2-4 weeks after blood counts recover
Radiation-induced: Resolves 2-6 weeks after completing radiation
No permanent damage in most cases

Potential Lasting Effects from Head/Neck Radiation

Xerostomia (dry mouth): Damage to salivary glands, can be permanent
Taste changes: May persist for months, usually improves
Fibrosis: Scarring and stiffness of tissues
Increased dental cavities: Due to dry mouth
Osteoradionecrosis: Rare bone damage requiring preventive dental care

Psychological Impact

Severe mucositis can cause significant distress
Fear of eating due to pain
Impact on social activities (talking, eating with others)
Anxiety about future treatment cycles
Support from psychologist/counselor can help

Frequently Asked Questions

How long will my mouth sores last?

For chemotherapy-induced mucositis, sores typically appear 5-10 days after treatment, peak around days 7-14, and resolve within 2-4 weeks as your white blood cells recover. For radiation therapy to the head and neck, mucositis usually begins in weeks 2-3 of treatment, worsens during treatment, peaks 1-2 weeks after completion, and heals over 2-6 weeks. Most patients see complete resolution, though radiation can cause longer-lasting effects.

Can I prevent mouth sores?

While you can't always prevent mucositis entirely, you can significantly reduce your risk and severity. The most important strategy is excellent oral hygiene - brushing with a soft toothbrush after every meal, rinsing frequently with baking soda solution, and keeping your mouth moist. For specific chemotherapy drugs like 5-FU bolus or melphalan, sucking on ice chips during and for 30 minutes after infusion can reduce mucositis risk by 40-50%. See your dentist before starting treatment to address any existing problems.

What is magic mouthwash and how do I use it?

Magic mouthwash is a prescription compounded solution that typically contains lidocaine (numbing agent), diphenhydramine (antihistamine), and an antacid (Maalox or Mylanta) to coat and soothe. The recipe varies by pharmacy. To use, swish about 5-10 mL (1-2 teaspoons) in your mouth for 1-2 minutes, then either spit out or swallow depending on your doctor's instructions. Use it 15-30 minutes before meals to numb your mouth for eating, and as needed for pain. Effectiveness varies among patients.

Should I use mouthwash like Listerine?

No, avoid alcohol-based commercial mouthwashes like Listerine or Scope during cancer treatment. The alcohol is very drying and irritating to already sensitive mouth tissues and can actually worsen mucositis. Instead, use a gentle baking soda rinse (1 teaspoon baking soda + 1 teaspoon salt in 1 quart warm water) or plain saline several times daily. If you want to use a commercial product, choose alcohol-free options like Biotene.

What can I eat when my mouth hurts?

Focus on soft, bland, moist foods at cool or room temperature. Good options include: scrambled eggs, yogurt, cottage cheese, mashed potatoes, oatmeal, cream soups, smoothies, protein shakes, applesauce, and pudding. Add gravies, sauces, or butter to make foods easier to swallow. Avoid acidic foods (citrus, tomatoes), spicy foods, salty or crunchy foods (chips, crackers), and very hot foods. Small, frequent meals are easier than three large ones. Use magic mouthwash 15-30 minutes before eating to numb your mouth.

When should I call my doctor about mouth sores?

Call immediately if you have: fever of 100.4°F or higher (may indicate infection), severe pain not controlled by medications, inability to eat or drink anything (risk of dehydration), difficulty swallowing even liquids, excessive bleeding from mouth, white patches that won't rinse off (possible fungal infection), or signs of dehydration (dizziness, very dark urine, extreme dry mouth). Don't wait - these symptoms require prompt medical attention, especially if you have low white blood counts.

Can I still brush my teeth if I have mouth sores?

Yes, and you should! Continuing to brush is very important even with mucositis, as good oral hygiene helps prevent infection and promotes healing. Use an extra-soft or ultra-soft toothbrush and be very gentle. If your platelets are very low (<50,000) or your gums bleed easily, you may need to use foam swabs instead of a brush. Brush at least 4 times daily (after each meal and at bedtime) and rinse with baking soda solution frequently. Never stop oral care completely.

Will the sores come back with every chemotherapy cycle?

Not necessarily. Some patients develop mucositis with the first cycle but not subsequent ones, while others experience it with every treatment. Your risk depends on the specific drugs, doses, your individual sensitivity, and how well you maintain oral hygiene. If you had severe mucositis, tell your oncologist - they may adjust your chemotherapy dose, add preventive measures (like ice chips if appropriate), or prescribe medications to reduce severity. Each person's experience is different.

Medical Disclaimer

The information provided on this page is for educational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.

If you think you may have a medical emergency, call your doctor or 911 immediately. Oncol.net does not recommend or endorse any specific tests, physicians, products, procedures, opinions, or other information that may be mentioned on this site.

Sources and References

National Cancer Institute. Oral Complications of Chemotherapy and Head/Neck Radiation (PDQ®). Updated 2024.
Multinational Association of Supportive Care in Cancer (MASCC). Clinical Practice Guidelines for Mucositis. 2024.
Lalla RV, et al. MASCC/ISOO Clinical Practice Guidelines for the Management of Mucositis Secondary to Cancer Therapy. Cancer. 2014;120(10):1453-1461.
Peterson DE, et al. Management of Oral and Gastrointestinal Mucosal Injury: ESMO Clinical Practice Guidelines. Ann Oncol. 2015;26(Suppl 5):v139-v151.
Villa A, Sonis ST. Mucositis: Pathobiology and Management. Curr Opin Oncol. 2015;27(3):159-164.
Blijlevens N, et al. Prospective Oral Mucositis Audit: Oral Mucositis in Patients Receiving High-Dose Melphalan or BEAM Conditioning Chemotherapy. J Clin Oncol. 2008;26(9):1519-1525.
Barasch A, Peterson DE. Risk Factors for Ulcerative Oral Mucositis in Cancer Patients. J Support Oncol. 2003;1(1):21-33.
Spielberger R, et al. Palifermin for Oral Mucositis after Intensive Therapy for Hematologic Cancers. N Engl J Med. 2004;351(25):2590-2598.