Chemotherapy Mouth Sores: Causes, Prevention, and Care

Chemotherapy can cause mouth sores, also called oral mucositis, and this is a well‑recognized side effect. ^[1] These sores can be painful, look like burns, and make it hard to eat, drink, talk, and even breathe in severe cases. ^[2] They may appear on the lips, gums, tongue, inner cheeks, and roof or floor of the mouth, and sometimes extend into the esophagus. ^[2] In some people, severe sores can lead to dehydration, weight loss, infections, and even delays or changes in cancer treatment, so early prevention and care are important. ^[3]

What Are Mouth Sores (Oral Mucositis)?

• Oral mucositis refers to inflammatory and/or ulcerative lesions of the mouth lining caused by anti‑cancer treatments. ^[4] The mouth’s lining renews quickly, and chemotherapy can damage these rapidly dividing cells, leading to redness, pain, and ulcers. ^[5] Symptoms typically include mouth pain, visible sores, bleeding, and a higher infection risk when the mouth’s protective barrier is broken. ^[6]

Who Is at Higher Risk?

• Risk varies by the chemotherapy drugs, dose, and whether treatments are combined. ^[7] Conventional chemotherapy causes mucositis in about 20%–40% of people, with higher rates in intensive regimens and bone marrow transplant settings. ^[7] Certain agents such as fluorouracil (5‑FU), capecitabine, methotrexate, cytarabine, doxorubicin, etoposide, melphalan, irinotecan, and bleomycin are more commonly linked to clinically significant mucositis. ^[7] Targeted therapies (for example, some tyrosine kinase inhibitors and mTOR inhibitors) can also cause mouth inflammation or stomatitis. ^[8] Individual factors like smoking, alcohol use, dry mouth, poor oral hygiene, and combined chemo‑radiation can increase severity. ^[9]

What Symptoms to Watch For

• Burning or soreness in the mouth, red or white patches, and ulcers that look like shallow craters. ^[2] Pain that interferes with eating or swallowing; in more severe grades it can limit oral intake and require modified diets or IV fluids. ^[10] Fever with mouth sores can signal infection and needs urgent medical assessment. ^[6]

Prevention Strategies

• Oral cooling (cryotherapy): Swishing or holding ice chips or cold water in the mouth during certain chemotherapy infusions (such as short‑infusion 5‑FU) can reduce drug delivery to the oral mucosa and lower sore risk. ^[11]
• Preventive medications: Depending on your regimen, your care team may recommend specific agents to lower risk; these are considered for select treatments and risk levels. ^[11]
• Consistent mouth care: Gentle, regular oral hygiene helps decrease irritation and infection risk during therapy. ^[6]

Daily Mouth Care Routine

• Brush gently 2–3 times daily with a soft‑bristle brush; if brushing is too painful, try foam swabs temporarily. ^[6]
• Use bland rinses frequently: dissolve 1/4–1/2 teaspoon of salt and/or baking soda in 8 oz (240 mL) of water and swish several times a day; avoid alcohol‑based mouthwashes that can sting. ^[6]
• Keep lips moisturized with a non‑irritating balm to prevent cracking. ^[6]
• Stay hydrated with cool fluids; choose soft, moist foods and consider high‑calorie, high‑protein options if intake drops. ^[6]
• Avoid triggers: spicy, acidic, rough, or very hot foods; alcohol and tobacco can worsen irritation and delay healing. ^[6]

Pain Relief and Symptom Control

• Topical anesthetics and coating agents can numb painful areas short‑term to help with eating and oral care. ^[6]
• “Magic mouthwash” is a commonly used compounded rinse that may include an antihistamine (for swelling), an antacid or coating agent, a local anesthetic, and sometimes an antifungal or corticosteroid; it can ease pain for some people, though effectiveness varies and it should be used as directed by your oncology team. ^[12]
• Systemic pain medicines (such as acetaminophen or prescribed analgesics) are often added when pain is moderate to severe to maintain nutrition and hydration. ^[6]

When to Call Your Care Team

• Inability to drink enough fluids, severe pain that prevents eating, signs of dehydration, or weight loss should prompt a call right away. ^[3] Fever, worsening redness, pus, or foul odor from sores can indicate infection and needs prompt evaluation, especially if white blood cell counts are low. ^[6] Severe mucositis (grade 3–4) can be dangerous and may require urgent interventions and treatment adjustments. ^[10]

Nutrition Tips That Help

• Choose cool or room‑temperature soft foods: yogurt, smoothies, scrambled eggs, oatmeal, mashed potatoes, and well‑cooked pasta. ^[6]
• Try high‑protein shakes if chewing is difficult, and sip frequently throughout the day to maintain hydration. ^[6]
• If weight is dropping despite efforts, ask about a dietitian referral for tailored strategies and supplements. ^[6]

How Clinicians Assess Severity

• Clinicians often use standard grading (CTCAE):
  • Grade 1: mild, no intervention needed
  • Grade 2: moderate pain/ulcers, modified diet
  • Grade 3: severe pain, limits intake
  • Grade 4: life‑threatening complications, urgent care needed. ^[10]
• Grading guides treatment decisions, including stronger pain control, infection prevention, nutritional support, and potential therapy adjustments. ^[10]

Key Takeaways

• Mouth sores from chemotherapy are common and range from mild irritation to severe, treatment‑limiting ulcers. ^[1] Early, gentle oral care, cooling strategies during certain infusions, and timely pain control can meaningfully reduce discomfort and complications. ^[11] If sores are severe, limit eating, or are accompanied by fever, reach out to your oncology team promptly for personalized care. ^{[3] [6]}

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Table: At‑a‑Glance Care Plan for Chemo‑Related Mouth Sores

• What it is: Oral mucositis (inflammation/ulcers of the mouth lining during cancer therapy). ^[4]
• Common triggers: Certain chemo drugs (e.g., 5‑FU/capecitabine, methotrexate, cytarabine, irinotecan), high‑dose regimens, combined treatments. ^[7]
• Daily care: Soft brush, bland rinses (salt/baking soda in water), lip balm, avoid alcohol‑based mouthwashes. ^[6]
• Food and drinks: Cool, soft, non‑spicy; high‑protein shakes; frequent sips to hydrate. ^[6]
• During infusion: Ice chips or cold water with specific regimens to lower risk. ^[11]
• Medications: Topical anesthetics/coaters; compounded “magic mouthwash” as prescribed; systemic pain control when needed. ^{[12] [6]}
• Red flags: Fever, inability to drink/eat, weight loss, worsening pain contact your team urgently. ^{[3] [6]}