When you get chemotherapy for breast cancer, you’ll very likely run low on white blood cells called neutrophils. Doctors call this neutropenia. It’s a normal part of going through chemo.

With neutropenia, you’re more likely to get infections and fever. That’s because neutrophils are part of your body’s front-line immune response. So with fewer of them available to fight off threats, you’re more vulnerable.

Keep in mind that neutropenia is a temporary side effect of chemo – and you can take simple precautions to help avoid catching an infection.

Do these things to help protect yourself:

• Get all your vaccinations that your doctor recommends. This includes the flu shot and the COVID-19 vaccine and boosters. Ask about other vaccines, like those for hepatitis B and pneumonia. If you’re getting chemotherapy, your immune system needs the help no matter what your age is.
• Wash your hands often.
• Avoid contact with people who you know to be sick. Do this even if they say they feel OK or aren’t infectious anymore.
• Avoid busy indoor spaces. “If you need to go to an indoor place like church or the grocery store, wear a mask and limit the amount of time you’re there as much as you can. I would even suggest wearing a mask if you’re at a crowded outdoor event,” says Jeremy Pappacena, PharmD, a clinical pharmacy specialist in hematology and oncology at Allegheny Health Network in Pennsylvania.
• Prepare your food carefully. Cook food thoroughly. “Avoid having meats on the rarer side or things like sushi or other uncooked fish, and wash and scrub raw fruits and vegetables,” Pappacena says.
• Have the people help protect you. Ask family members and others who live with you to follow similar precautions as much as possible.

You don’t have to take your temperature every day during chemotherapy. But if you notice symptoms of infection – like feeling flushed or chilled, being short of breath, or feeling weak or otherwise unwell – tell your doctor.

If you develop a fever while getting chemotherapy, call your doctor immediately and tell them your symptoms.

“They might tell you that everything is OK, or they might want you to go to your doctor’s office or nearest emergency department,” says Nan Chen, MD, a breast cancer specialist at the University of Chicago. “If you go to the ED, be sure to tell the doctor there that you are on chemotherapy.”

How severe neutropenia is and how long it lasts varies. It partly depends on the kind of chemotherapy you’re getting, Pappacena says.

“Most people see their lowest points of neutropenia somewhere around the middle of their treatment cycle,” Pappacena says. “If you’re getting chemo every 4 weeks, then your neutropenia will usually be at its lowest around 2 weeks after the last treatment. It definitely can get worse as treatment continues.”

The main treatments that doctors use to help shorten neutropenia and protect you from infection are medications called G-CSFs (granulocyte colony-stimulating factors). You usually get them by injection about 24 hours after a dose of chemotherapy.

“If we are giving chemotherapy that has a moderate or high risk of leaving you neutropenic for many days, we will give you G-CSF medication after chemotherapy to bump up your white blood cells,” Chen says.

For most people who get chemotherapy that can cause neutropenia, doctors prescribe long-acting G-CSF medications. With long-acting G-CSF medication, you only have to have one injection after each chemotherapy treatment. You can either go back to the cancer center where you got your chemotherapy for your injection the next day, or you can self-inject the medication at home (or have a partner inject it for you).

A newer option for delivering long-acting G-CSFs is called Onpro. It comes in a kit with a prefilled syringe inside a blister pack that is applied to your skin (usually on your upper arm). Your health care provider prepares an area of skin and applies the on-body injector pack. They will insert a short needle that delivers the medication under your skin about 27 hours later.

“Once the injector is activated, it will slowly administer the medication over about 45 minutes,” Pappacena says. “You have to be careful not to accidentally knock it off or take it off too soon so that you don’t get a full dose of the medication. There’s a nice little ‘fuel gauge’ on the package so that you know when the medication is fully dispensed. When it says ‘Empty,’ then you can take it off and dispose of it.”

“If you are uncomfortable with using a needle yourself and don’t want to have to go back to the doctor’s office the next day for an injection, this is a good option,” Chen says.

There are also shorter-acting G-CSF medications that need multiple injections between doses of chemotherapy.

“Those have mostly fallen out of favor with the availability of longer-acting medications that only require one shot,” Pappacena says. “But some patients might have more severe side effects with the longer-acting agents, and for them we might try the shorter-acting drugs.”

The most common side effects of G-CSFs are usually bone and muscle pain and a mild fever. “Usually, these can be managed by taking a nonsteroidal anti-inflammatory drug, or even an over-the-counter anti-allergy medication,” Chen says.

Chemo is strong medicine that doesn’t just affect your cancer.

“Chemotherapy works against cancer cells because it is designed to kill cells that are rapidly dividing, like cancer cells,” Chen says. “But some of the healthy cells in your body also divide quickly, including white blood cells called neutrophils that are very important in the body’s defense against infection.”

When bacteria or viruses enter your body, “neutrophils are among the first cells to respond, quickly dividing to mount an immune response,” Chen says. “So they’re very vulnerable to medications that kill rapidly dividing cells.”

Just remember that it’s to be expected with chemo. “Neutropenia tends to follow a pretty typical pattern, and your doctor will know how to manage it,” Chen says.