How Do Chemo and Radiation Affect the Immune System?

Chemotherapy and radiation are two of the most common and effective treatments for cancer, but they can weaken your immune system for months after treatment. That makes you vulnerable to illness and infection.

This article will go over changes to the immune system after chemo and radiation, the risks of these treatments, what to do about treatment effects, and when to seek medical help.

Doctor talking to cancer patient

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How Does Cancer Treatment Affect the Immune System?

Chemotherapy (chemo) and radiation therapy (also called radiotherapy) kill cancer cells. The problem is, they also kill rapidly dividing healthy cells.

Each treatment has its own effects. When the two treatments are combined, which is common, you can end up with side effects of both.


Chemotherapy is a systemic treatment, meaning it affects your whole body. Many types of chemo are given as injections or infusions. It can also be given by mouth, in pill form.

Cancer cells grow and divide quickly. Chemo is designed to go after fast-growing cells like cancer.

However, it can’t tell one fast-growing cell from another. That means it kills many types of cells in your body.

That includes bone marrow cells. One of their jobs is to produce white blood cells for the immune system. White blood cells are responsible for attacking and killing viruses, bacteria, and other pathogens. But when chemo kills off bone marrow cells, your immune system doesn’t have enough white blood cells to fight off infections.

The most common chemo-related problem is neutropenia. This is a decrease in neutrophils (white blood cells), which are important for immunity.


Chemotherapy kills fast-growing cells, including cancer and bone marrow cells. Damage to bone marrow means it can't produce disease-fighting immune-system cells. Low white blood cell counts (neutropenia) can result.


Radiation works differently than chemo. It exposes your cells to high doses of radiation (high-energy beams) that damage their DNA (genetic material).

This means cells either die or become unable to divide, which is how cells reproduce. This shrinks tumors or slows their growth.

As with chemo, healthy cells are damaged by radiation, too. But radiation may have less of a damaging effect on the immune system in general. That's because radiation isn't systemic. Rather, it is targeted right at your tumor.

Oftentimes, however, radiation does have to travel through areas of healthy cells to get to the tumor, so either those cells or cells nearby the tumor can be affected.

Metastatic Disease

When cancer spreads, called metastasis or metastatic disease, the whole body may need radiation. This causes a reduction in the immune system's ability to fight off infection, called immunosuppression, much more like that of chemotherapy.

Depending on where the tumor being treated is located in the body, radiation may directly damage your immune system. It may also cause other conditions that harm the immune system.

For example, radiation near the underarm can damage lymph nodes, which are part of the immune system. The damage can lead to an increased risk of infection in the arm.

Radiation can deal a lot of damage when it’s aimed at bones. The effect on bone marrow is similar to that of chemo. Neutropenia is common.


Radiation damages cellular DNA. This kills cancer but can impair immune-system cells. Effects are usually milder than with chemo but are also less predictable. Immune system damage may be direct or caused by complications of radiation.

How Strong Is Your Immune System After Cancer Treatment?

After chemo and radiation, your immune system can stay suppressed for several months. 

A study of people who had chemo for breast cancer found the immune system often took nine months or more to fully recover. Several types of immune-system cells were depleted.

In people who smoked, some immune cells were only at 50% of normal levels after nine months. That’s compared to an 80% rate in nonsmokers.

Researchers say the immune-system damage could leave you vulnerable to some illnesses even if you’ve been vaccinated. These include tetanus (a bacterial infection) and pneumonia (inflection causing inflammation of the air sacs of the lungs).

Specific chemo drugs have different effects. In the study, people given the drug anthracycline (a type of chemotherapy that is an antibiotic) had normal immune function by the end of the study period. Those who took anthracycline plus taxane, a more traditional chemo drug, recovered much more slowly.

While newer research has been illuminating, much remains to be learned about the specific immune-system effects of cancer treatments. 


It can take months for the immune system to rebound after chemo and radiation. The specific drug(s) can make a difference in recovery time. Smokers tend to recover more slowly.

Ways to Support Your Immune System After Chemo and Radiotherapy

After chemo and/or radiation it’s important to protect yourself from infection. You can do this by:

  • Getting a flu shot every year
  • Getting a COVID-19 vaccination
  • Following COVID-19 prevention strategies even if you’re vaccinated (wearing a mask, washing hands, sanitizing, social distancing, and avoiding sick people and crowds)
  • Getting enough sleep
  • Eating a healthy diet
  • Avoiding unpasteurized dairy, cooking meat well, washing produce thoroughly
  • Avoiding animal waste, such as from cleaning a litter box or picking up dog feces, or soil contaminated with them
  • Not changing diapers
  • Staying as active as you safely can
  • Managing your stress
  • Treating cuts and scrapes properly

Also, ask your care team if you’d benefit from medicine to increase your white blood cell count.

Managing Comorbidities

If you have other medical conditions (comorbidities), make sure you manage them well during and after cancer treatment.

When to Seek Professional Treatment

It’s important to get treatment for illness or infection right away. Symptoms to watch for include:

  • Fever and chills/sweats
  • Vomiting
  • Diarrhea
  • Sore throat
  • Cough
  • Nasal congestion
  • Pain, redness, swelling, and warmth anywhere in your body

If you go to urgent care or the emergency room for treatment, be sure to tell the staff you’ve had cancer and what kind of treatments you have had. This will help them understand the seriousness of the situation.

Lasting Side Effect

Healthy cells damaged by chemotherapy generally heal well once treatment ends. An exception is nerve cells in your hands and feet. They can have permanent damage that leads to a painful condition called peripheral neuropathy.


Chemotherapy kills fast-growing cells, which includes many healthy cells, along with cancer cells. Bone marrow cells are frequently damaged and unable to produce white blood cells. This hampers your immune system.

Radiation damages the genetic material of cells. This kills both cancer and immune-system cells. Effects tend to be less than with chemo. Radiation may directly damage the immune system or may cause other conditions that impair your immunity. Much of this depends on where the cancer is.

Your immune system may take months to rebound after chemo and radiation. Be sure to take steps to protect yourself from infection. If you notice symptoms of infection, get medical attention right away.

A Word From Verywell

More people are surviving and thriving after cancer all the time. Once you beat the disease, though, you can’t let up your guard. Impaired immunity can pose a real threat.

Just being aware of the problem is a start. Adopting good habits, enlisting friends and family to help, and staying in touch with your care team can help you stay healthy until your immune system is strong enough to protect you again.

Frequently Asked Questions

  • Do chemo and radiation affect the immune system permanently?

    No, effects aren't permanent. It takes time, but the immune system does recover. The amount of time that takes varies by treatment type, duration, and other factors. One study found normal or near-normal immune function within nine months of ending chemo.

  • Do chemo and radiation shorten your lifespan?

    Research suggests cancer and its treatments may shorten life expectancy by 30%. A major review of studies found causes of death among cancer survivors included complications of treatment such as:

    • Heart disease
    • Pulmonary fibrosis (lung scarring)
    • Hormone-related disease

    Researchers suspect cancer treatments may mimic the effects of aging.

  • How long does it take for your immune system to go back to normal after chemo and radiation?

    Most people recover a large amount of immune function within nine months of chemo. It may take longer for smokers.

    Radiation's effects are less predictable. Ask your care team what to expect based on the tumor's location and the type of radiation you had.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American Cancer Society. Why people with cancer are more likely to get infections. Updated March 13, 2020.

  2. Cancer Treatment Centers of America. How do cancer treatments damage the immune system. Updated May 7, 2020.

  3. National Institutes of Health, National Cancer Institute. Radiation therapy to treat cancer. Updated January 8, 2019.

  4. How radiation therapy affects the immune system. Updated August 15, 2014.

  5. Verma R, Foster RE, Horgan K, et al. Lymphocyte depletion and repopulation after chemotherapy for primary breast cancer. Breast Cancer Res. 2016;18(1):10. Published 2016 Jan 26. doi:10.1186/s13058-015-0669-x

  6. Verma R, Foster RE, Horgan K, et al. Lymphocyte depletion and repopulation after chemotherapy for primary breast cancer. Breast Cancer Res. 2016;18(1):10. Published 2016 Jan 26. doi:10.1186/s13058-015-0669-x

  7. Centers for Disease Control and Prevention. Know the signs and symptoms of infection. Updated November 10, 2020.

  8. How chemotherapy affects the immune system. Updated September 4, 2014.

  9. Cupit-Link MC, Kirkland JL, Ness KK, et al. Biology of premature ageing in survivors of cancer. ESMO Open. 2017;2(5):e000250. Published 2017 Dec 18. doi:10.1136/esmoopen-2017-000250

By Adrienne Dellwo
Adrienne Dellwo is an experienced journalist who was diagnosed with fibromyalgia and has written extensively on the topic.