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Fever during chemotherapy

Is 99, 100 or 101 Degrees — an Emergency?

A fever during chemotherapy is not the same as an ordinary fever. It can mean your white blood cell count has fallen and your body cannot fight infection — which is a medical emergency. The number on your thermometer tells you what to do right now.

Medically reviewed by Dr. Owais Mohammed, Medical Oncologist · Last reviewed September 2026

  • Different from an ordinary fever — Chemotherapy lowers white blood cells. Without them, your body cannot fight infection the normal way.
  • One reading is enough — You do not need repeated readings to act. A single high reading is enough to call or go now.
  • Both scales covered — Every threshold below is given in Fahrenheit and Celsius so you can act on what your thermometer shows.
  • Never wait until morning — Fever during chemotherapy can become life-threatening within hours. Call tonight.
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The threshold, per NCCN and ASCO guidance, is 100.4°F (38°C) on any reading — call your oncology team now — or 101°F (38.3°C) on a single reading — go to hospital now without waiting for a callback. You do not need to measure twice. One reading at or above these numbers is enough to act.

If a symptom below applies to you, do not wait for a callback. Call 1800-202-8726 or go to your nearest emergency department.

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Our helpline is answered by clinical staff. If a symptom is on the list above, do not wait for a callback — call, or go to your nearest emergency department.

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Not sure whether this counts as an emergency?

Call the helpline. It is always better to check than to wait.

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What should I do right now?

  • Take your temperature orally — under the tongue — not under the arm, which reads lower.
  • Note the reading and the time you took it.
  • Check the table below for your exact number.
  • 101°F (38.3°C) or above: go to hospital now. Do not call first.
  • 100.4°F (38°C) or above: call your oncology helpline now, even in the middle of the night.
  • Do not take paracetamol or any fever medicine before calling — it can mask how serious the infection is.
  • Have your chemotherapy card and the helpline number ready before you call.

What does each temperature reading mean?

Your readingWhat it meansWhat to do
Below 99°F / 37.2°CBelow thresholdWatch closely. Call your team immediately if it rises or you feel unwell.
99°F / 37.2°CMild elevation — not yet at thresholdCheck again within one hour. Call if it rises any further, or if you feel unwell at all.
100°F / 37.8°CClose to the action thresholdCall your oncology helpline now. Do not wait for another reading.
100.4°F / 38°CAt the NCCN and ASCO thresholdCall your oncology helpline now — tonight, not in the morning.
101°F / 38.3°C or aboveEmergency threshold on a single readingGo to hospital now. Do not wait for a callback.
Any reading with shaking chills, breathing difficulty, or confusionEmergency regardless of the numberGo to hospital now.
Typically startsOften within the first two weeks after a chemotherapy dose, when white blood cells reach their lowest point. This is when fever is most dangerous.Do not wait to see if it passes. Call tonight.

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Common questions

Frequently asked questions

Is 100°F (37.8°C) dangerous on chemotherapy?

Yes, and it needs a call tonight. 100°F is close enough to the action threshold that your oncology team needs to know now. Fever during chemotherapy can rise quickly — especially in the one to two weeks after a dose, when white blood cells are at their lowest. Call your helpline even if you are not sure whether it counts.

Do I need two readings to confirm it, or is one enough?

One reading is enough. NCCN and ASCO guidance for febrile neutropenia does not require a sustained fever before you act. A single reading of 100.4°F (38°C) means call your team now. A single reading of 101°F (38.3°C) means go to hospital — do not wait for a second reading to confirm it.

Can I take Crocin or paracetamol first to bring the temperature down?

No — not before speaking to your team. Paracetamol lowers your temperature and can make the situation look less serious than it is, which delays the assessment and treatment you actually need. Call first. Your oncology team will tell you what to take and when.

My thermometer reads under the arm. Is that reliable?

Armpit readings tend to be lower than oral readings, which means you may underestimate a fever if you are measuring there. If your armpit reading reaches 100°F (37.8°C) or above, treat it as being at the threshold and call your oncology helpline now. When you have any doubt about the reading, call — your team would rather hear from you than have you wait.

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