Cancer treatments can increase infection risk

Most cancer treatments used today can increase the risk of infection.


Any type of major surgery can suppress the immune system within hours of surgery. Anesthesia (the drugs used to make the patient sleep) may play a role. It might take from 10 days to many months for the immune system to recover completely.

Surgery also breaks the skin and mucous membranes and can expose internal tissues to germs. The wound caused by surgery (the incision) is a common place for infection.

Because surgery is often used to diagnose, stage, or treat people with cancer, it’s important to know that surgery can increase the risk of certain infections. Things that raise the risk of infection after surgery include:

  • How long the person is in the hospital
  • The extent of the surgery (how much cutting was done)
  • How long the operation took
  • The amount of bleeding during surgery
  • The person’s nutritional status
  • Prior cancer treatment, such as chemotherapy or radiation or medical problems such as diabetes, or heart or lung problems

People with cancer may get antibiotics before and for a short time after having surgery to help protect them from infection.


Chemotherapy (often called chemo) is the most common cause of a weakened immune system in people getting cancer treatment. The effects on the immune system depend on many things, including:

  • Which chemo drugs are used
  • Chemo dose (how much of each drug is given at once
  • How often chemo is given
  • Past cancer treatments
  • The person’s age (older people are more likely to get infections, with or without cancer)
  • The person’s nutritional status
  • The type of cancer
  • How much cancer there is (the stage of the cancer)

Some drugs affect the bone marrow and immune system more than others. But chemo drugs can have different effects on how well the body makes white blood cells, red blood cells, and platelets. In most cases, white blood cells are the ones most affected by chemo. (See How does your body normally resist infections? for more on the bone marrow and blood cells.) After treatment ends, your blood cell counts usually go back to normal over time.

Radiation therapy

The effects of radiation therapy on bone marrow cells can be much like the effects of chemo. It also can cause low white blood cell counts, which increases the risk for infections.

Many things affect how radiation therapy affects the immune system, such as:

  • The total radiation dose
  • The radiation schedule
  • The part of the body being treated with radiation
  • How much of the body is treated with radiation

Total body irradiation or TBI (where a person’s entire body is treated with radiation) is the only type of radiation likely to cause very low white blood cell counts. This type of radiation may be used during the bone marrow or stem cell transplant process.

Radiation is most often given to just one part of the body, so the whole immune system isn’t damaged by it. Still, depending on the dose and the part of the body being treated with radiation, the skin or mucous membranes may be damaged, so you’re less able to keep germs out.

Today, radiation treatments are most often given over many sessions rather than in one large dose. This helps decrease the amount of skin and tissue damage, immune suppression, and the risk of infections.


Immunotherapy is sometimes used to make your immune system better able to recognize and attack cancer cells. This can be done by helping your own immune system work harder or smarter, or by giving you things like man-made immune system proteins. Immunotherapy is sometimes used by itself to treat cancer, but it’s often used along with or after another type of treatment to add to its effects.

These treatments promote immune reactions against cancer cells, but sometimes they change the way the immune system works. Because of this, people who get biologic therapies may be at risk for immune suppression.

When certain white blood cell (lymphocyte) levels are low, the chance of getting certain serious viral and fungal infections becomes very high. Other white blood cell counts may drop, too. Most of the time they return to normal after treatment stops, but the lymphocyte counts can stay low for months.

Stem cell transplant (bone marrow transplant)

Stem cell transplant (SCT) is the term now used to include bone marrow transplant (BMT), peripheral blood stem cell transplant (PBSCT), and umbilical cord blood stem cell transplant (UCBSCT). These transplants allow doctors to use very high doses of chemo and/or total body irradiation (TBI) to try to kill all the cancer cells in the body.

In the process of killing the cancer cells, the blood-forming stem cells of the patient’s normal bone marrow are also killed. Because of this, stem cells (either from the blood or bone marrow) are removed from the patient and saved before the high-dose chemo is given. Or, stem cells may be taken from a donor or banked umbilical cord blood. Once the cancer cells are killed, the saved or donated stem cells are given to the patient so that blood cells can be made and the immune system rebuilt.

High-dose chemo used with TBI causes more severe immune weakness that lasts for a longer time. It can also damage the skin and mucous membranes and make them less able to keep germs out of the body.

For more information on these types of transplants, see Stem Cell Transplant for Cancer.

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