Why are Cancer Patients at Increased Risk for Infection?

Infection is the most common complication of cancer and cancer treatment. Having cancer raises your risk of experiencing a serious infection because of the changes happening in the immune system. Even a small wound can become a medical emergency for a person with cancer.

These changes in the immune system are due to cancer itself, treatments, poor nutrition, and other chronic health problems.

This article will describe why individuals with cancer are at an increased risk of developing infections and what to do about it.

Risk of Serious Infections Due to Cancer - Illustration by Jiaqi Zhou

Verywell / Jiaqi Zhou

Cancer and the Immune System

The immune system is made up of organs, cells, and proteins that work together to protect our bodies from infection. An infection can be caused by bacteria, viruses, protozoa, or fungi. 

The body has several ways of protecting itself from infection, including:

  • Skin: The skin is the body’s largest organ and protects the body from infection. When there is a cut or tear in the skin, it is easier for an infection to enter the body.
  • Mucous membranes: Mucous membranes are the moist tissues that line the inside of the nose, mouth, throat, eyelids, digestive system, urethra, and vagina. Mucous membranes protect our bodies from infection when we breathe and eat. Some cancer treatments can damage the cells in the mucous membranes, leading to open sores. 
  • White blood cells: Once an infection enters the body through the skin or mucous membranes, the immune system’s job is to fight it off. The white blood cells are an important part of the immune system and include neutrophils, lymphocytes, monocytes, and macrophages. These cells recognize and attack invaders that cause infection.

People with cancer are more likely to experience infections in the following body parts:

  • Skin
  • Mucous membranes
  • Mouth 
  • Digestive tract
  • Lungs
  • Bladder
  • Kidneys
  • Brain
  • Spinal cord 

Because cancer can change the immune system, people with cancer are at an increased risk of developing a serious infection. Certain types of cancer affect the immune system’s response to infections. For example, Hodgkin lymphoma, non-Hodgkin lymphoma, multiple myeloma, and most types of leukemia begin in white blood cells and cells that regulate the immune system. When these cells are not able to function normally, they are less likely to effectively fight infections. 

Other types of cancer may grow on the skin or mucous membranes. This damages those protective tissues and raises the risk of an infection entering the body.

Finally, some cancers change the way the immune system functions. Mutated cancer cells can change healthy immune cells and make them interfere with the immune system itself. When cancer cells spread to the bone marrow, they attack and compete with healthy cells. When too many bone marrow cells are destroyed, they cannot make white blood cells to fight off infection. 

Recap

Certain types of cancer change the immune system and the way it responds to germs. These changes raise the risk of infection.

Cancer Treatments Can Increase Risk

Most cancer treatments change the way the immune system works. This can lead to an increased risk of infection. The most common cancer treatments include:

  • Chemotherapy: Chemotherapy is designed to kill cancer cells and is the most common cause of a weakened immune system in those with cancer. That is because chemotherapy also damages healthy immune cells in the process. Chemotherapy is known to decrease the number of neutrophils in the blood. This is called neutropenia and raises the risk of infection. 
  • Radiation: Radiation raises the risk of infection because it also can damage healthy cells and may lower the number of white blood cells in the body. Total body irradiation affects the entire body and is the most likely type of radiation to raise the risk of infection. 
  • Surgery: Surgery for any reason weakens the immune system. A surgical incision can become infected and lead to infection entering the body. Anesthesia may affect the immune system’s function for months. If you are undergoing surgery for cancer, your doctor may recommend taking antibiotics to lower your risk of infection. 
  • Targeted therapy: Targeted therapy is designed to help the immune system by targeting specific cancer cells or proteins on the cells. However, these therapies may also change how the immune system works.
  • Immunotherapy: Immunotherapy works by boosting the immune system’s response to better recognize and fight cancer cells. By doing this, some immunotherapy treatments change the way the immune system works, which may raise the risk of infection.
  • Stem cell therapy: Stem cell therapy is used in cancer treatment to replace cells in the bone marrow that were destroyed by chemotherapy or radiation. People who require a stem cell transplant are at increased risk for infection because their immune systems have been significantly weakened by high-dose chemotherapy or total body irradiation. 
  • Steroids: Medications like steroids suppress the immune system and raise the risk of serious infection. 

If the increased risk of infection is due to cancer treatment, then the risk is usually temporary. Once the treatment is finished, the immune system should recover over time. 

Other Increased Risk for Infection in Cancer Patients

In addition to the immune system changes due to cancer and cancer treatments, there are other factors that raise the risk of infection in people with cancer. 

Nutrition 

It is common for people with cancer to experience poor nutrition. When our bodies don’t receive the nutrients they need, the cells cannot grow and work normally. This affects immune cells and their ability to fight infection.

People with cancer usually need more nutrition than they used to because of their treatment side effects. Your immune system needs extra calories and protein to have the energy and fuel to fight cancer cells. After surgery, your body needs an adequate supply of nutrients to heal. 

People with cancer often experience poor nutrition because of:

  • Nausea and vomiting from chemotherapy
  • Painful mouth sores from chemotherapy and radiation
  • Difficulty eating and drinking due to cancer of the mouth, throat, or digestive system 

If you have been experiencing poor nutrition during cancer treatment, talk with your healthcare provider. Your medical team may include a dietician to help you increase your nutrients and help your body heal. 

Immunosuppression 

Most people with cancer have a compromised immune system because of either cancer treatments or cancer itself. When the immune system is suppressed, it is less capable of fighting off infections. To know how susceptible you are to infections, your healthcare provider will regularly monitor your neutrophil count. 

Other Factors

When our bodies are under stress, they are not able to function normally. Cancer causes considerable stress in a person’s life. Emotional stress and lack of sleep are both factors that can affect the immune system’s function and raise the risk of infection.

Call your healthcare provider right away if you experience a fever or feel unwell during your cancer treatment period. Any sign of infection needs to be assessed and treated urgently. 

Summary 

People with cancer are at an increased risk for infection because their immune systems cannot function properly. In addition, cancer, cancer treatment, poor nutrition, and other factors can all increase infection risk. If you develop a fever or any sign of infection during treatment, seek medical care right away. 

A Word From Verywell

Being diagnosed with cancer has likely been one of the most stressful periods of your life. This is an overwhelming time, and having to worry about further complications like the risk of infection may feel like too much. Know that your body is not as capable of fighting off infections right now, so it is essential to monitor yourself for any signs, such as a fever. Talk with your healthcare provider about how to protect yourself from infection.

Frequently Asked Questions

  • Are people with cancer at higher risk for COVID?

    People with cancer are at a higher risk of developing severe illness from COVID-19. Talk with your healthcare provider about how to lower your risk of being exposed to the virus and other steps that you can take to protect yourself. Wash your hands frequently, avoid crowds, and ask your doctor if you are eligible for the COVID-19 vaccine. 

  • Can cancer cause frequent infections?

    Yes, people with cancer can experience frequent infections because their immune systems are not working normally. This may be due to treatment side effects or cancer itself. 

  • How do you assess the risk for infection?

    Your healthcare provider and medical team will stay in regular contact with you to monitor your cancer symptoms and any treatment side effects. To assess your risk of infection, your healthcare provider will order a blood test to measure your neutrophil count. Neutrophils are white blood cells that fight infection. 

  • What infections are common in cancer patients?

    People with cancer are more likely to experience infections in the following body parts:

    • Skin
    • Mucous membranes
    • Mouth 
    • Digestive tract
    • Lungs
    • Bladder
    • Kidneys
    • Brain
    • Spinal cord
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5 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. Causes of infections (germs).

  2. American Cancer Society. Why people with cancer are more likely to get infections.

  3. Johns Hopkins Medicine. The immune system

  4. Centers for Disease Control and Prevention. Preventing infections in cancer patients.

  5. National Cancer Institute. Coronavirus: What people with cancer should know.

Additional Reading