Fever During Chemotherapy: Why It Can Be Urgent

This page is for people having chemotherapy and their caregivers. It explains why a fever matters, which temperature to act on, and when to get care.

A fever during chemotherapy can be a medical emergency. Chemotherapy can lower the white blood cells that fight infection. With fewer of them, an infection can become life-threatening, and it needs urgent medical attention. Most cancer teams give each patient a specific temperature and a written plan for what to do. The CDC says a fever during chemotherapy may mean an infection, that this is a life-threatening condition, and that you should be seen quickly.

This page does not replace the exact instructions your care team gave you. Follow those first, and treat a fever as something to act on right away, not later in the day.

Chemotherapy can reduce neutrophils, a type of white blood cell that fights infection. Doctors call a low neutrophil count neutropenia. When neutrophils are low, your body has a much harder time containing an infection that a healthy immune system would handle easily. The CDC notes that a fever may be the only sign that you have an infection. That is why cancer teams treat it as urgent rather than waiting to see what happens.

The CDC says to call your doctor immediately if you have a temperature of 100.4°F (38°C) or higher. Your own team may have given you a lower number as part of your personal plan. If so, follow their number. One reading at or above the number is enough to call. If you were never given one, ask for it now, and use 100.4°F (38°C) as your number until you have a specific answer. The CDC also says to take your temperature any time you feel warm, flushed, chilled, or not well.

If you can do it quickly and safely, note your temperature, the time you took it, and any other symptoms: chills, a new cough, pain, or burning when you urinate. This detail helps your team make decisions fast once you reach them. Recording these details should never come before calling. If you are unsure whether to record first or call first, call first.

Do not wait to see if the fever passes. During chemotherapy, a fever is not something to sit on, even if you feel otherwise okay. Do not take fever-reducing medicine before checking with your team. The National Cancer Institute says to talk with your doctor or nurse before taking any medicine for a fever, even acetaminophen or ibuprofen.

Most cancer teams give patients a written threshold and clear instructions: who to call, what number to use during the day, and what number to use after hours or on weekends. That personal plan is the authority here, not this page or any general guideline. If you do not have one, ask for it at your next contact with your team, and do not wait for a fever to happen first.

• Call your care team right away, at any hour, if your temperature reaches 100.4°F (38°C), or the lower number your team gave you. The CDC says, "If you get a fever during your chemotherapy treatment, it's a medical emergency" (CDC). One reading is enough. This is the call their after-hours number exists for. It is not a wait-until-morning call and not a wait-until-office-hours call. If nobody picks up within a few minutes, go to the emergency room and say at the desk that you are on chemotherapy.
• Call 911 if a fever or shivering comes with confusion, shortness of breath, a racing heart or weak pulse, or clammy, sweaty skin. The CDC lists these as possible signs of sepsis, a life-threatening medical emergency, and they cannot wait for a phone call to be returned. Do not drive yourself.
• Call your care team right away, at any hour, even without a fever, if you have any of these signs of infection: chills or sweats, a new or changed cough, a sore throat or new mouth sore, shortness of breath, a stuffy nose, a stiff neck, burning or pain when you urinate, peeing more often, unusual vaginal discharge, diarrhea, vomiting, pain in your belly or rectum, or any new pain. The same goes for redness, soreness or swelling anywhere, including a surgical wound or where a catheter or port enters your body. The CDC lists all of these as reasons to call your doctor right away during chemotherapy (CDC).
• Call your care team right away, at any hour, even without a fever, if you notice other signs of infection the National Cancer Institute lists, such as sores or a white coating in your mouth or on your tongue, or cloudy or bloody urine. NCI says infections during cancer treatment can be life-threatening and need urgent medical attention, so do not wait until morning or wait to see if they settle.

Whichever route you take, tell the staff you are on chemotherapy and may have a low white blood cell count. The CDC says to tell the person checking you in at the emergency room that you are a cancer patient having chemotherapy, because a fever may mean an infection and you should be seen quickly.

• What exact temperature should make me call you or go to the ER?
• What number do I call, day or night?
• When in my treatment cycle are my white blood cells expected to be lowest?
• Are there other symptoms, besides fever, that you want treated as urgent?

This page is general education, written from CDC and NCI guidance and checked against those sources. It is not medical advice, and it is not a substitute for your own care team's emergency instructions.

• National Cancer Institute — Infection and Neutropenia During Cancer Treatment
• CDC — Watch Out for Fever
• CDC — Neutropenia and Cancer Treatment
• CDC — About Sepsis