Medical Oncologist
Urgent care
Gut infections during chemotherapy
Fever is the difference that matters. Loose motions from the drugs come without a fever, follow the cycle and settle. Loose motions with a fever, during the days when white cells are low, may be an infection in the bowel wall — one of the most dangerous situations in chemotherapy care, because the lining is thin and there are almost no white cells to defend it. Early treatment usually goes well; waiting does not.
NG
Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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The short answer
How is a gut infection different from ordinary loose motions?
Fever is the difference that matters. Loose motions from the drugs themselves come without a fever, follow the rhythm of the cycle, and settle. Loose motions with a fever, during the days when white cells are low, may be an infection in the bowel wall, and that is one of the most dangerous situations in the whole of chemotherapy care.
It is dangerous because the bowel lining is thinned by the treatment and the body has almost no white cells to defend it. Bacteria can cross into the bloodstream quickly. People who are managed early usually do well; people who wait until morning sometimes do not.
What this means in practice
Any fever during chemotherapy is an emergency, and a fever alongside loose motions or stomach pain is more urgent still. Do not take an anti-diarrhoeal, do not start a leftover antibiotic, and do not give paracetamol and wait to see whether the night passes.
Keep a thermometer in the house from the first cycle and use it properly. "He feels a bit warm" is not something a team can act on.
!
Go to the emergency department now
A fever, with or without loose motions · loose motions with severe stomach pain · a swollen, hard or very tender stomach · blood in the motions · vomiting where nothing stays down · shivering uncontrollably · dizziness, a racing heart or breathlessness · very little urine passed since the morning. Go to the nearest emergency department and say clearly that the person is on chemotherapy. Do not give paracetamol first, do not take an anti-diarrhoeal, and do not start an antibiotic left over from a previous illness.
Not sure whether this applies to you?
Ask an oncologistTelling them apart
Side effect, or infection?
More likely the treatment itself
Treat as infection until proven otherwise
No fever at any point
Any fever, however mild it seems
Starts a few days after a cycle and eases
Comes on suddenly, or keeps getting worse
Mild cramping that eases after a motion
Severe stomach pain, or a hard tender stomach
No blood, motions otherwise normal in colour
Blood in the motions, or black tarry motions
Drinking normally, passing urine normally
Not keeping fluids down, or passing little urine
Alert, steady, otherwise themselves
Shivering, drowsy, confused or dizzy standing
What they can be
The gut infections that matter during treatment
Listed so you understand what your team is looking for. They are told apart by tests, not by symptoms at home.
Infection of the bowel wall during low counts
The most serious. Fever, stomach pain and loose motions during the days when white cells are lowest. It needs hospital treatment, antibiotics into a vein and close observation, started quickly.
Never at home
- No anti-diarrhoeal
- No waiting until morning
Infection after antibiotics
Antibiotics given for something else can clear the normal gut bacteria and let a harmful one take over, causing frequent watery motions and cramping. It is treatable, and it is diagnosed on a stool test.
Always mention any antibiotics taken recently, even for an unrelated problem.Ordinary food and water infections
These do not stop happening because someone is on chemotherapy, and they hit harder when counts are low. Street food, pre-cut fruit, unsafe water and food left standing are the usual routes.
Viral gut infections
Picked up from family or visitors. In someone with normal immunity they pass in a day or two; during the low-count days they cause far more dehydration and need reviewing rather than riding out.
What to expect
What happens when you go in
It moves faster than people expect, and that is deliberate. Blood is taken to check the counts and for infection markers, blood cultures are sent, and if the white cells are low, antibiotics are started immediately rather than waiting for results. Waiting for confirmation costs more than it saves.
What else is done
Fluids into a vein to correct dehydration. A stool sample to identify what is causing it. An examination of the stomach, and often a scan if there is significant pain or tenderness. The bowel may be rested — nothing by mouth for a period — while things settle.
What to take with you
Every medicine in the house including anything bought over the counter, the chemotherapy schedule or treatment card, recent blood reports, your written record of motions and temperatures, and details of any antibiotics taken recently. Take the family member who knows the answers.
Say the words at the desk
"On chemotherapy, with a fever." That sentence changes how quickly someone is seen in any emergency department in the country, and it is worth saying at reception rather than waiting to be asked in the queue.
Most people treated early recover well and return to treatment. The delay is what causes harm, not the infection alone.Leave a number, we will call you
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Being straight with you
What this page cannot tell you
It cannot tell you whether what you have is an infection. Loose motions from the drugs and loose motions from an infection feel much the same from the inside, which is exactly why the rule is built around fever rather than around how the symptoms feel. Blood tests and a stool sample are what separate them.
It also cannot tell you how low your counts are on any given day. That is why the safest approach during chemotherapy is to treat a fever as an emergency every time, rather than trying to judge whether this particular day is one of the risky ones.
What to do next
Keep a thermometer in the house and check the temperature properly whenever anything is wrong. Write the helpline number where the whole household can see it, and decide now which hospital you would go to at night. Ask your team when your counts are expected to be lowest, and treat those days with particular care around food and water.
Questions we are asked
Common questions about gut infections
Why can we not just take an anti-diarrhoeal and see?
Because slowing the gut keeps an infection inside it rather than letting it clear, and during the low-count days that can let bacteria cross into the bloodstream. With a fever present, this is one of the genuinely dangerous self-medication decisions in cancer care.
Is it safe to wait until the morning clinic?
No, not with a fever. Infection during low counts can move quickly overnight, and emergency departments are used to seeing patients on chemotherapy at any hour. A night spent waiting is what turns a treatable problem into an admission to intensive care.
How do we lower the risk at home?
Freshly cooked hot food, nothing left standing, no street food, no pre-cut fruit, and boiled or bottled drinking water. Handwashing before eating and cooking, by everyone in the house. Keep visitors with coughs, colds or upset stomachs away during the low-count days.
He has loose motions but no fever. Do we still call?
Call if they are increasing through the day, if fluids are not keeping up, if there is blood or severe pain, or if he is passing little urine. Mild loose motions that are settling, with normal drinking, can usually be managed at home — but do not take an anti-diarrhoeal without your team's say-so.
Can family members catch it?
Some gut infections spread within a household, which is why handwashing and separate towels matter. The greater risk usually runs the other way — a family member's ordinary stomach upset hitting someone with no white cells to fight it. Anyone unwell should keep their distance during the low-count days.
Will this delay the next cycle?
Probably, and that is the right decision rather than a setback. Your oncologist will want the infection cleared and the counts recovered before continuing, and may adjust what comes next. Delays for infection are a normal part of treatment and most people resume.
What temperature counts as a fever?
Ask your own team for the reading they want you to act on, and write it down, because units set slightly different thresholds. Whatever the number, shivering uncontrollably, feeling suddenly very unwell or a rapidly rising temperature all warrant going in regardless of what the thermometer says.
Should we keep antibiotics at home just in case?
Only if your team has specifically given them to you with instructions, which does happen for some patients. Otherwise no. Starting an antibiotic before assessment masks the fever, confuses the blood cultures and can delay the right treatment being chosen.
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Sources
- National Cancer Institute — Gastrointestinal Complications (PDQ)
- Cancer Research UK — Infections and cancer treatment
- Macmillan Cancer Support — Infection and cancer treatment
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
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