Constipation & diarrhoea from cancer treatment in children — what every parent needs to know

This is one of the most common calls paediatric oncology teams receive. After a chemotherapy infusion — especially one that includes anti-nausea medicines — the bowel often slows. If your child has not passed a stool for two to three days and is not in significant pain and the abdomen is soft, contact your care team during normal hours to ask whether to start a stool softener. Do not give any over-the-counter laxative, suppository, or enema without checking first — some preparations are not safe during chemotherapy, and some protocols have specific bowel management medicines already built into the plan. Increasing fluids gently and encouraging light movement (even a short walk if the child feels well enough) supports the bowel while you wait for guidance.

When constipation is accompanied by marked abdominal pain, a noticeably distended or hard belly, or vomiting, call your child's oncology team the same day — even outside normal clinic hours if your unit has an on-call number. In children whose blood counts are very low (neutropenia), severe constipation can occasionally be a feature of a serious condition called neutropenic enterocolitis (typhlitis) — an inflammation of the bowel wall that requires prompt hospital assessment. Most cases of pain with constipation are straightforward, but the combination of low blood counts and abdominal pain with no stool for several days is one that your oncology team needs to know about promptly so they can decide whether your child needs to come in for examination and possibly an abdominal X-ray.

Mild diarrhoea — around two to four extra loose stools above your child's normal pattern in a day — is common in the days following certain chemotherapy drugs. With mild diarrhoea and no fever or blood in the stool, the focus at home is on keeping fluids up. Give small, frequent sips of water or oral rehydration solution (ORS) rather than large amounts at once. Temporarily avoid high-fibre foods, raw fruits and vegetables with skins, dairy products other than plain yoghurt, and anything spicy or fatty. Plain rice, boiled banana, and plain toast or roti are generally well tolerated. Let your team know at the next clinic visit or call if it continues beyond 24 hours or worsens — they may advise a stool culture to rule out an infection.

Blood or mucus in a child's stool during cancer treatment is always a reason to call your oncology team immediately — do not wait until morning or the next scheduled appointment. In a child whose bowel lining has been made fragile by chemotherapy, blood in the stool can indicate significant mucosal damage (mucositis of the gut). It may also signal an infection from a bacterium that is particularly dangerous in children with low immunity, such as Clostridium difficile (C. diff). Dark, tar-like stools rather than bright red blood can indicate bleeding higher up in the gut. None of these need to be confirmed before calling — the presence of any blood or mucus in stool is a threshold that warrants immediate contact with your care team or, out of hours, the hospital emergency department.

Children dehydrate faster than adults. The warning signs to watch for are: a dry mouth and tongue, no tears when crying, sunken eyes, skin that does not spring back quickly when gently pinched, not passing urine for eight hours or more, or unusual drowsiness. If your child has been having diarrhoea and shows any of these signs, go to the hospital emergency department or call your oncology on-call number without waiting. Children on chemotherapy who develop significant dehydration may need intravenous fluids and monitoring. If the child also has a fever above 38°C at the same time as diarrhoea and dehydration, that is an oncology emergency — call immediately. Fever during a period of low blood counts (febrile neutropenia) always requires urgent assessment regardless of what else is happening.

Some children on longer-term treatment cycles experience a pattern where the bowel swings between being slow and over-active — sometimes constipated for several days, then loose stools once the backup clears, then slowing again. This alternating pattern can be confusing for parents and may also reflect the timing of anti-nausea medicines relative to the bowel's recovery between cycles. Keeping a simple written record of your child's bowel movements — frequency, consistency, and whether any pain accompanies them — is genuinely useful to share with your oncology nurse. It helps the team identify whether the bowel is moving in a pattern that matches the chemotherapy schedule, and allows them to adjust laxatives or diet advice accordingly. There is no embarrassment in discussing this: the oncology team ask about bowel health at every cycle because it matters for your child's comfort and safety.