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Cancer and cancer treatments can weaken the immune system. The immune system is a complex system the body uses to resists infection by germs, such as bacteria or viruses.
When the immune system is weakened, there is a higher risk for infection. Because of this, infection is a common complication of cancer and cancer treatment, and certain types can be life-threatening if not found and treated early.
If you're getting treatment for cancer, your cancer care team will talk to you about any increased risk for infection you may have, and what can be done to help prevent infection. Usually the risk is temporary because the immune system recovers after a period of time, but each person is different.
For cancer patients who finished treatment a few years ago or longer, their immune systems have most likely recovered. But this depends a lot on the type of cancer you had, the type of treatment you received, and other medical problems you might have that can affect your immune system.
Different cancer treatments can affect people in different ways. Each patient's immune system responds to, and recovers from, treatment differently. The US Centers for Disease Control and Prevention (CDC) provides guidance for cancer patients, caregivers, and their health care teams about how to prevent infection. Patients with cancer, those in active treatment, and those who have finished any type of treatment may need to take special precautions to prevent infections from viruses and bacteria. They can look at the CDC information and talk to their cancer care team to find out if special precautions are needed, such as if they need to limit or avoid social activities or wear any protective equipment (masks, gloves, etc.).
If you are getting any type of treatment for cancer or previously had cancer that was treated with surgery, radiation therapy, chemotherapy, targeted therapy, immunotherapy, hormone therapy, stem cell or bone marrow transplant, or have used any other types of treatments, it is best to discuss your risk of getting an infection with a doctor who understands your situation and medical history.
Here are some things you can do that might help prevent infection and illness when your immune system is weak due to cancer and/or cancer treatment:
Be aware of and watch for signs and symptoms of infection. Talk to your doctor about what you should watch for and what you need to report right away.
Infections can be picked up from food and drinks. So, food safety is very important when your immune system is weaker than normal. Talk to your cancer care team about whether you need to follow a special diet during your cancer treatment. Wash your hands before handling any food products. Make sure all meat products (this may include chicken, beef, and other meat products) are cooked thoroughly to kill any bacteria that may be present.
Fresh fruits and vegetables can have germs on the outside which can cause illness. Some doctors tell their patients who have weak immune systems not to eat any fresh fruits or vegetables to help lower the risk of infection. Others allow their patients to eat fresh fruits and vegetables as long as they are washed thoroughly first. It’s important to know that even when the outer part of a fruit (such as the peel or rind) isn’t eaten, it still needs to be washed before it’s peeled. If it isn’t, germs can get on the part that is eaten when the peel or rind is cut. It may also be a good idea to avoid certain foods that have been linked to outbreaks before, such as raw vegetable sprouts, fresh salsa, and berries. Be careful eating at salad bars, as they have been sometimes associated with certain bacterial infections.
Talk with your doctor about any dietary questions or concerns you may have, or ask to talk with a registered dietitian. For more detailed information about safely handling foods, see Food Safety During Cancer Treatment
Sometimes, doctors prescribe medicines when a person’s immune system is very weak – even though there’s no sign of infection. The drugs are given to help keep you from getting an infection.
Anti-bacterial, anti-viral, and/or anti-fungal drugs may be used to help prevent infection. You may hear this called prophylactic antibiotic use, or just prophylaxis. Prophylaxis is only used when there’s a very high risk of getting infections (the immune system is very weak). You might also be given antibiotics if you are taking other medicines that can weaken your immune system, such as a long course of steroids or certain chemotherapy drugs.
The preventive drugs are stopped when your immune system is no longer so weak (often some time after the immune-weakening drugs are stopped). Using antibiotics in this way does not prevent all infections. That means it’s still important to use the same precautions as when you aren’t taking preventive drugs, and be sure to tell your doctor about any new signs of infection.
Growth factors are proteins your body makes to help your blood cells grow. They are also known as colony-stimulating factors (CSFs) or myeloid growth factors. Growth factors stimulate the bone marrow to make more white blood cells to help the body fight infection. You can be given injections of man-made CSFs. They are most often used after chemo to help prevent infection. Your doctor also may give you a CSF if your immune system is weak and you have a serious infection that’s getting worse even though you’re getting treatment.
Growth factors can have side effects in some people, but they can reduce the risk of infection in the patients who need them. Talk to your cancer care team about the risks and benefits of CSFs. Talk to your cancer care team about what side effects you might have while using CSFs and what you can do to manage the side effects.
Many cancer treatments and cancers can cause changes in your blood counts. A low white blood cell (WBC) count can put you at higher risk of infection.
The WBC count measures your body’s ability to fight infection. There is usually a total WBC count reported in lab results. When your total WBC count is low, you’ll need to watch for signs of infection so that you can get treatment right away. There can also be different types of WBCs reported in lab results underneath the total WBC count. Neutrophils are one of the most important types of WBC counts in a lab report because when they are low, your risk for infection is higher. Monocytes are another type of WBC. A high number of monocytes can mean you have an infection and that your body is helping to fight it by making more monocytes.
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.
Balducci L, Shah B, Zuckerman K. Neutropenia and thrombocytopenia. In DeVita VT, Lawrence TS, Rosenberg SA, eds. DeVita, Hellman, and Rosenberg’s Cancer: Principles and Practice of Oncology. 11th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2019:2069-2076.
Brant JM, Stringer LH. Neutropenia & infection. In Brown CG, ed. A Guide to Oncology Symptom Management. 2nd ed. Pittsburgh, PA: Oncology Nursing Society; 2015:377-378
Centers for Disease Control and Prevention. Preventing infections in cancer patients. 2018. Accessed at https://www.cdc.gov/cancer/preventinfections/index.htm on March 25, 2020.
Freifeld AG, Kaul DR. Infection in the patient With cancer. In Niederhuber JE, Armitage JO, Kastan MB, Doroshow JH, Tepper JE, eds. Abeloff’s Clinical Oncology. 6th ed. Philadelphia, PA: Elsevier; 2020:544-562.
National Comprehensive Cancer Network (NCCN). Prevention and treatment of cancer-related infections. 2018. Version 1.2019. Accessed at https://www.nccn.org/professionals/physician_gls/PDF/infections.pdf on August 27, 2019.
Palmore TN, Parta M, Cuellar-Rodriguez J, Gea-Banacloche JC. Infections in the cancer patient. In DeVita VT, Lawrence TS, Rosenberg SA, eds. DeVita, Hellman, and Rosenberg’s Cancer: Principles and Practice of Oncology. 11th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2019:2037-2068.
Last Revised: August 25, 2023