Chemotherapy can lower the levels of infection-fighting white blood cells, a condition known as neutropenia. Your doctor is going to be most concerned with your level of neutrophils, the most abundant of the different types of white blood cells. These cells contain tiny packets filled with potent chemicals called enzymes that can destroy bacteria when the chemicals are released. Bacteria are the most common source of infection for patients receiving chemotherapy. The normal number of white blood cells in one microliter of blood (a tiny droplet, one millionth of a liter) is between 4,000 and 11,000; the risk of infection is increased when the neutrophil count drops to 1,000 or fewer. If your neutrophil count dips below this number, you might experience chills, fever, or sweats.

If you are feeling unwell in any way after receiving chemotherapy, it’s important to take your temperature. Temperatures from 99°F (37.2°C) to 100°F (37.8°C) are fairly common. But if your temperature rises to 100.5°F (38.1°C) or above, call your doctor or nurse immediately. Fever may be your only sign of an infection. Unless fever is treated promptly, infections can become life-threatening. Make sure you have a good thermometer that is easy to use and read (the digital ones are fine). Also, be sure to have your doctor’s telephone number in case there is a problem.