What are infections and who is at risk?

Infections are caused by germs (also called microbes or microorganisms) that enter the body, multiply, and cause harm, illness, or even death. The main types of germs are bacteria, viruses, protozoa (some of which act as parasites), and fungal organisms (also called fungi).

Cancer itself can increase your risk of getting a life-threatening infection. So can certain types of cancer treatment. Once the cancer is gone and treatment is over, the risk of infection usually goes back down. For most people with cancer, the greatest risk of getting a serious infection only lasts for a limited time. And most people with cancer are not at a high risk of getting the kinds of serious infections described here. Your risk of infection also depends on the type of cancer you have and the treatment you get. For example, surgery does not weaken a person’s resistance to infection nearly as much as a bone marrow transplant. And some chemotherapy drugs are less likely than others to affect a person’s ability to resist infection. (See What makes people with cancer more likely to get infections? for more on this.)

Infections that develop in people who have cancer or who are getting cancer treatment can be more serious than those in people who are otherwise healthy. They can also be harder to treat. If you have cancer, it’s important to find and treat infections early, before they get worse and spread. This information can help you learn what to look for and what to do if you do get an infection. This is one part of a series on information about cancer patients and their risk of infection.

This information is about people with cancer and their risk of infection. If you are looking for information on infections that can cause cancer, see Infections That Can Lead to Cancer.

Know your risk of infection

It’s important to weigh the risk of infection and other side effects against the benefits of cancer treatment. Talk with your doctors before or during chemotherapy or radiation therapy to see how this information applies to you. Here are some questions you can ask your doctor or cancer care team before and during cancer treatment:

  • Will this cancer treatment make me more likely to get infections?
  • Will you do anything special to help keep me from getting infections during treatment?
  • What can I do to lower my risk of infection?
  • How will I know if I have an infection?
  • What kinds of infections are most common for someone in my situation?
  • What should I do if I think I have an infection?
  • If I get a fever, does that mean I have an infection?
  • How will you decide how to treat my infection?
  • What will you do if the treatment doesn’t get rid of my infection?
  • What are the likely side effects of the treatments for infection?

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Medical Review: February 16, 2015 Last Revised: February 25, 2015