Mouth sores during chemo — care & relief for your child

The inside of your child’s mouth — the cheeks, gums, tongue, and throat — is lined by a thin layer of cells that replaces itself every seven to fourteen days. Chemotherapy works by targeting cells that divide and grow rapidly. Cancer cells divide fast, which is why chemotherapy is effective. But the mouth lining also divides fast, so chemotherapy affects it too.

When the mouth lining breaks down faster than it can repair itself, the result is oral mucositis — painful inflammation that can progress to open ulcers. Mouth ulcers from chemotherapy in children are not caused by a virus or bacteria, and they are not contagious. They are a direct side effect of how the medicines work. In medical grading systems, mucositis is scored from Grade 1 (mild redness, some discomfort) through Grade 4 (so severe that the child cannot swallow at all and needs hospital support).

Not every child on chemotherapy develops significant mouth sores. The severity depends on which medicines are used, the doses given, and individual factors in how your child’s body responds. Your child’s oncology team will warn you in advance if the planned regimen is known to carry a higher risk of mucositis. This is one of the most predictable side effects of treatment, which means it can be prepared for and managed — you are not facing this without a plan.

Mucositis can also affect the lining of the gut — causing nausea, abdominal cramping, or diarrhoea — because the same rapidly dividing cells line the digestive tract. This page focuses on mouth sores child chemo parents most commonly ask about: the visible, painful ulcers in the mouth and throat. If your child is also experiencing significant digestive symptoms, raise these at the next oncology visit, as they may need separate management.

Keeping your child nourished when they have painful mouth ulcers during chemotherapy is one of the most challenging parts of home care. The goal during this period is to maintain calorie and fluid intake in the least painful way possible. You are not aiming for a normal diet — you are aiming for enough.

Foods that are easier to manage with mouth sores: smooth yoghurt, room-temperature or cool porridge, mashed potato or banana, scrambled eggs, soft rice, custard, milkshakes blended without citrus fruit, smoothies made from banana or mango, soft-boiled or poached fish, ice cream, ice lollies, and soft idli or soft dosa soaked in mild dal. Cool or room-temperature foods are typically more comfortable than hot foods, because heat increases blood flow to already-irritated tissue.

Foods and drinks to avoid: anything with sharp edges (dry biscuits, toast, crisps, papadums), acidic items (citrus fruit and juice, tomatoes, tamarind, raw mango), spicy foods, very hot foods and drinks, alcohol (including in cooking for older teenagers), and carbonated beverages. These all worsen inflammation and pain in already-damaged tissue. Salty foods can sting but small amounts of salt in rinsing water are fine — the concentration in food is typically higher.

Some children find that drinking through a straw reduces the contact between acidic or flavoured liquids and painful areas. Others prefer wide-rimmed cups to avoid touching the lips. Let your child guide you on what feels least painful — they will often have strong preferences, and honouring those gives them a sense of control during a period when much is out of their hands.

Internal link: for broader guidance on supporting your child through the full treatment period, visit our page on caring for your child on chemo at home, or return to the paediatric cancer overview for information on all aspects of childhood cancer care at CION.