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Fever During Chemo: Neutropenic Fever and When to Get Help Now

A fever during chemo can feel scary, especially in the middle of the night. Here's the most important thing to know: a fever is a reason to call right away, not to wait and see. Calling early isn't overreacting. It's exactly what your care team wants you and your family to do.

ℹ️ General information to help you and your loved ones talk with your care team, not medical advice. Read our disclaimer.

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🌡️ The number to remember: 100.4°F (38°C)

If your temperature is 100.4°F (38°C) or higher, call your cancer care team right away, day or night, even if you feel OK. This is the threshold the CDC uses. Your team may give you a different number; if they do, follow theirs.

Call 911 for trouble breathing, chest pain, confusion, or fainting.

Why fever is an emergency during chemo

Many chemo drugs lower your neutrophils (infection-fighting white blood cells). This is called neutropenia (low white blood cells). When they're low, your body can't fight germs well, and a fever may be the first, or only, sign of infection. Neutropenic fever (fever with low white blood cells) can turn serious quickly, so care teams treat it fast, often with antibiotics within an hour of arrival. Learn more in our guide to Neutropenia (low blood counts and infection risk).

✅ Call-now checklist

Call your care team right away if you have any of these during treatment:

A temperature of 100.4°F (38°C) or higher
Chills, shaking, or sweating, even without a high reading
A new cough, shortness of breath, or sore throat
Burning or pain when you pee, or cloudy urine
Redness, swelling, warmth, or pus around a port, IV site, or wound
New diarrhea, belly pain, or vomiting that won't stop
Mouth sores that make it hard to eat or drink
Feeling dizzy, weak, or "just not right"

📞 What to have ready when you call

Your temperature and when you took it
The name of your chemo and the date of your last treatment
Any other symptoms and when they started
Your drug and allergy list

Your team may tell you to come to the clinic or go to the ER. Tell the ER staff right away, "I'm on chemo and have a fever." Bring your wallet card or treatment list if you have one.

🌡️ How to check your temperature

Keep a reliable digital thermometer at home, and check whenever you feel warm, chilled, or unwell.
Use an oral thermometer. Don't take rectal temperatures during chemo unless your team says to.
Wait about 30 minutes after eating, drinking, or smoking.
Write down each reading and the time.

🏠 Lowering your infection risk

The CDC's advice for people getting chemo comes down to a few everyday habits:

Wash your hands often, and ask everyone around you to do the same.
Stay away from people who are sick, and avoid big crowds when your counts are low.
Ask your team about flu and COVID-19 vaccines for you and your household.
Handle food safely: cook meat and eggs fully, and wash fruits and vegetables.
Let someone else clean the litter box, bird cage, or fish tank.
Ask whether a white blood cell booster shot is part of your plan.

💜 How loved ones can help

Save the after-hours number in your phone, and keep a thermometer handy.
If they have a fever, make the call together instead of waiting until morning.
Keep a go-bag ready with their medicine list, a phone charger, and a snack.
Stay home if you're sick, or wear a mask and wash your hands often.

Questions people often ask

What temperature is a fever during chemo?

The CDC says to treat a temperature of 100.4°F (38°C) or higher as a fever and call your care team right away, any time of day or night. Your team may give you a different number, so follow their plan.

Should I take Tylenol (acetaminophen) for a fever during chemo?

Call your care team before taking anything. Fever-reducing medicine can hide a fever your team needs to know about. Many teams also ask you to avoid ibuprofen or aspirin when counts are low.

When should I go to the ER instead of calling?

Call 911 or go to the nearest ER if you have trouble breathing, chest pain, confusion, fainting, or you can't reach your team. Otherwise, call your team first, and they'll tell you where to go.

When are counts usually lowest?

For many chemo regimens, white blood cells are lowest about 7 to 12 days after treatment (often called the nadir), but it varies. Ask your team when your low point is likely.

What is neutropenic fever?

Neutropenic fever (fever with low white blood cells) means you have a fever while your neutrophils, the white blood cells that fight bacteria, are low. Infections can get serious fast, so it's treated as an emergency, usually with antibiotics right away.

Written by the Cancer Side Effects Guide team from FDA labels and leading cancer centers. Not medical advice. · Last updated: October 15, 2026 · How we write

Not medical advice. This page is general information to help you talk with your care team. It can't replace advice from your doctor or nurse. If you have a fever of 100.4°F (38°C) or higher during treatment, or any symptom that worries you, call your care team now. In an emergency, call 911.

Sources

Last updated: October 15, 2026. We summarize these sources in our own words.