Immunotherapy and Mouth Sores: Causes, Care, and When to Seek Help

Immunotherapy can cause mouth sores (oral mucositis) in some people. ^[1] Mouth sores are a known side effect across several cancer treatments, including chemotherapy, head and neck radiation, targeted therapy, bone marrow transplant, and immunotherapy. ^[2] These sores may range from mild irritation to painful ulcers that can make eating and drinking difficult. ^[2]

What mouth sores feel like and when they start

Mouth sores can appear on the tongue, lips, gums, inner cheeks, or throat and may feel swollen, tender, or ulcerated. ^[3] With immunotherapy, symptoms can start as early as 3 to 10 days after the first treatment in some cases. ^[3]

Why this matters

Severe mouth sores can interfere with oral intake, leading to pain, dehydration, and unintended weight loss, and sometimes may require adjusting cancer treatment. ^[2]

How to cope at home

• Rinse regularly: Swish a gentle solution every 4 to 6 hours (or more often if needed). ^[3] Use alcohol‑free, peroxide‑free mouthwash or a homemade rinse (1 teaspoon salt in 1 quart/4 cups water; you may add 1 teaspoon baking soda). ^[3]
• Oral hygiene: Use a soft‑bristled toothbrush to reduce trauma to the gums and oral lining. ^[3]
• Food choices: Avoid acidic, salty, or spicy foods, and foods that are very hot to the touch. ^[4]
• Habits: Don’t smoke or use tobacco products, as these can worsen irritation and delay healing. ^[4]
• Lip care: Keep lips moisturized with a simple lip balm to prevent cracking. ^[4]
• Consider oral cryotherapy: Ask your care team whether using ice chips (“oral cryotherapy”) around treatment times is suitable for you to reduce mucosal inflammation. ^[4]

When to call your care team

Contact your oncology team if you get mouth sores often, have pain with eating or swallowing, or cannot drink enough fluids to stay hydrated. ^[4]

How clinicians grade severity

Healthcare teams often use CTCAE criteria to grade mucositis severity:

• Grade 1: mild, no intervention needed
• Grade 2: moderate pain or ulcers, oral intake maintained (often with modified diet)
• Grade 3: severe pain that interferes with oral intake
• Grade 4: life‑threatening consequences, urgent intervention needed. ^[5]

Understanding your symptom grade helps guide treatment decisions, such as topical treatments, pain control, nutritional support, and whether cancer therapy needs to be paused or adjusted. ^[5]

Additional supportive measures you can discuss

• Pain control and topical therapies: Your team may suggest topical anesthetics, coating agents, or systemic pain relief to help you eat and drink more comfortably. ^[6]
• Professional oral care: Regular assessment and early management can reduce complications and improve comfort. ^[6]
• Evidence‑based guidelines: Clinical practice guidelines exist for preventing and managing mucositis caused by cancer therapies, and your oncology team will tailor strategies based on these standards and your treatment plan. ^[6]

Key takeaways

• Mouth sores can occur with immunotherapy, though not everyone will experience them. ^[1]
• Gentle, regular oral care and avoiding irritants are core self‑care steps. ^[3]
• Seek help promptly if pain limits eating/drinking or if sores are frequent or worsening. ^[4]