What to Know About Chemotherapy and Your Immune System

What to Know About Chemotherapy and Your Immune System

Reviewed by Jasper Clinical Board

Last updated 5/24/21

Chemotherapy affects almost every part of your body. And while this makes it a powerful tool for treating cancer, it also brings a slew of side-effects you’ll want to be aware of—especially when it comes to your immune system. 
Your immune system is an incredibly complex network that keeps you healthy by fending off invaders. Chemotherapy temporarily weakens this system, which can make you more vulnerable to infections—i.e., you become “immunocompromised.” 
For most people, this passes and immunity returns to normal after several weeks or months (depending on your overall health, your treatment course, and other factors). Until then, you’ll want to be very thoughtful about protecting yourself from bacteria, fungi, parasites, and viruses. We’ll dive into that below—but first, some background.

How doctors track your immune health

One of the key players in your immune system is called the neutrophil. This is a type of white blood cell that acts as a “first responder,” showing up and neutralizing dangerous invaders. During and after chemo treatments, your healthcare team will track your neutrophil numbers to understand your infection risk. 
This measurement is called your Absolute Neutrophil Count (ANC), and it ends up being a very important number. If your ANC is 1500 or above, you’re in the normal, healthy range. If it’s less than that, you may be diagnosed with “neutropenia”—a risky neutrophil shortage. Below 500 is considered severe neutropenia, and puts you in a very high-risk category for infections. 
Neutropenia occurs in 25-40% of first-time chemo patients, which makes it one of the most common side effects of chemotherapy. Even so, doctors take this condition very seriously. Infections of any type can be dangerous when you’re immunocompromised, so it’s best to act quickly and decisively. Call your doctor as soon as you notice any symptoms they’ve told you to watch out for (these might include fever, or excessive vomiting or diarrhea).

Infection risks & how to minimize them

While you’re immunocompromised, the major infection risks include:
  • Breaks in the skin. That means small cuts, injection or IV punctures, etc.
  • Communicable illnesses like the common cold, the flu, and Covid-19.
  • Foodborne illnesses contracted from unsanitary food or drinks.
  • Inhaled pathogens like mold and fungal spores.
To keep your infection risk low, closely follow your doctor’s advice around social distancing. Wash your hands frequently, avoid sick people, brush your teeth regularly (choose a soft or ideally extra soft brush, as your gums can be sensitive), and be scrupulous in washing your vegetables and handling raw meat, fish, and eggs to reduce the risk of food poisoning.

Some less common but still significant risks include: handling cat & dog litter, changing babies’ diapers, contact with fish tanks and reptiles (lizards, snakes, turtles), using communal baths / hot tubs, doing dusty construction / renovation work, gardening, and breathing spores from mulch, hay, or compost. (Note that some of these tasks, like gardening, might seem safer if you wear gloves, but you can still inhale spores from the soil). If you’re planning to travel abroad, check with your healthcare team first to assess the risks.

Boosting your immune system naturally

To build up your immune system during and after cancer treatment, you can trust in the same common-sense practices that you always hear about. That means getting as much sleep as you need, minimizing your daily stress, eating as healthfully as possible, exercising reasonably, and so on.
Wellness practices like yoga, meditation, massage, and relaxation techniques may also hold promise for enhancing your immune function and lessening some of the other unpleasant side effects of cancer treatment. Of course, you should always work closely with your healthcare team to ensure a wellness practice is safe and appropriate before getting started.

Medical options to strengthen your immune system

If you’re diagnosed with neutropenia, your healthcare team will likely consider a range of options. The first is called “antibiotic prophylaxis.” This simply means using antibiotics alongside your chemo treatments to ward off potential bacterial infections.
Another option is prescribing medication to boost your neutrophil numbers. These are called “colony-stimulating factors” (CSFs). Some brand-name examples are Neupogen (aka filgrastim), Neulasta (aka pegfilgrastim), and Leukine / Prokine (aka sargramostim).
Finally, you have the option to pause chemotherapy until your ANC returns to healthy levels. Although this is sometimes necessary, doctors avoid it when possible because it can make your chemotherapy less effective.

When to get medical attention

If you believe you have an infection, tell your healthcare team right away! As we said above, infections at this time can be very serious. 
It’s important to note that your body may not have the typical reaction to bacterial infections— such as redness, swelling, and pus—if you have neutropenia. So stay watchful and report any unusual feelings to your healthcare team. That includes chills, nausea, aches, and so on. 
Your doctor will probably ask you to take your temperature once or twice a day—and anytime you start to feel hot. If you have a fever above 100° F along with neutropenia, get medical attention immediately. Doctors call this condition “febrile neutropenia” and it is very serious. The standard treatment is an IV antibiotics course and hospitalization.

The content on this website is intended to provide the best possible information for you, but should not be considered—or used as a substitute for—medical advice. If you have questions about your diagnosis or treatment, please contact your health care provider(s). For questions or comments about this content, please email us at