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Side Effects

Causes of Infections (Germs)

Infection is one of the most common complications of cancer and cancer treatment. This is because cancer and cancer treatments can weaken the immune system for a period of time. An infection happens when germs enter the body, multiply, and cause the immune system to react.

The immune system is a group of organs, tissues, and cells that work together to resist and fight infections. Some infections can spread to other parts of the body and might become life-threatening if not found early. The main types of germs that can cause infections are: 

  • Bacteria
  • Viruses
  • Protozoa (some of which act as parasites)
  • Fungal organisms (also called fungi).

Certain types of cancer itself can increase your risk of getting an infection. For example, blood cancers such as lymphoma, leukemia, and multiple myeloma start in immune systemm blood cells. Read more about this in Why People with Cancer Are More Likely to Get Infections.

Certain types of cancer treatment can also cause you to have a higher risk of infection. Once the cancer cells are treated 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. But every patient is different and the side effects of treatments can be very different. So, your risk of infection depends on the type of cancer you have and the treatment you get. For example, surgery and radiation therapy do not weaken a person’s resistance to infection nearly as much as a bone marrow transplant that uses high doses of chemotherapy (chemo). And some drugs used to treat cancer are less likely than others to affect a person’s ability to resist infection.

Some infections can be very serious

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 and can lead to the person becoming seriously ill, and possibly dying.

One example is people who have recently received or are currently receiving immune-suppressive treatment and are bitten by a tick or mosquito that is carrying an illness. When infected with a tick-borne or mosquito-borne virus, these people are at higher risk for getting seriously ill and not recovering well.

If you have cancer, it’s important to find and treat infections early, before they get worse and spread. Talk to your cancer care team about your risk for infection.

Parts of the body most likely to get infection

Common sites of infection in people with cancer include :

  • The skin (anything that can cause a break in the skin, such as an injury, scrape, surgical incision, IV site, insect or other bug or animal bite)
  • Mucous membranes (soft linings, like inside the mouth, vagina, and intestines)
  • The digestive system (mouth, esophagus, stomach, and intestines)
  • The lungs and breathing passages (sinuses and throat)
  • The urinary system (bladder and kidneys)
  • The nervous system (brain and spinal cord)
  • The skin and tissue around a central venous catheter (CVC). A CVC is a tube or catheter put in a vein and used to draw blood and give IV drugs or fluids

Risk factors for infection

  • Neutropenia. Some types of cancer treatment, such as chemotherapy, radiation therapy, stem cell transplant, or bone marrow transplant can cause the immune system to be suppressed. Neutropenia (a decrease in the number of neutrophils, a component of white blood cells, in your blood). This means your immune system is weaker and your body may not be able to fight infections as well as it should.
  • Medications such as steroids can make your immune system weaker and increase your risk of infection.
  • Certain types of cancers, such as those that affect the bone marrow or those that can spread to the bone, may increase the risk of an infection. Ask your doctor if your cancer puts you at an increased risk for infection.
  • Mucositis. Irritation or soreness of the digestive tract lining. Patients with mucositis will often have mouth sores.
  • Having other medical conditions such as diabetes, chronic obstructive pulmonary disease (COPD), autoimmune disease, among others. If you have other medical conditions, ask your doctor if they put you at increased risk for infection.
  • Other factors, such as poor nutrition, stress, or lack of sleep.

Know your risk of infection

It’s important to weigh the risk of infection and other side effects against the benefits of cancer treatment. Each patient's situation is different because people with cancer might have other health problems that can affect how they respond to cancer treatment. Talk with your doctor before and during cancer treatment about your risk for infection. Here are some questions you can ask your doctor or cancer care team about infection:

  • Does my type of cancer or cancer treatment make me more likely to get infections? If so, when am I at increased risk?
  • What kinds of infections are most common for someone in my situation?
  • What signs or symptoms should I watch for and when should I call you?
  • What symptoms would need urgent care at the emergency room? If I have to go to the emergency room, is there anything special I need to tell the people who work there?
  • Will you do anything to help keep me from getting infections during treatment?
  • What can I do to lower my risk of infection?
  • If I get a fever, does that mean I have an infection?
  • How will you decide how to treat my infection?

Signs of infection in people with cancer

It’s important to watch for early signs of infection and tell your health care team about them right away. This way treatment can be started as early as possible to prevent the infection from spreading to other parts of the body. This is even more important for people who have a low white blood cell count (neutropenia).

Signs and symptoms of an infection might include:

  • Fever (higher than normal body temperature). Your cancer care team will tell you what temperature they consider a fever.
  • Shaking chills or sweats (often goes along with fever)
  • Sore throat
  • Sores or white coating on your tongue or in your mouth
  • Cough or shortness of breath
  • Nasal congestion
  • Burning or pain when urinating; bloody or cloudy urine
  • Redness, swelling, drainage, or warmth at the site of an injury, surgical wound, or IV such as a central venous catheter (VAD), or anywhere on the skin including the genital and rectal areas
  • Pain or tenderness in the stomach or abdomen (the belly)
  • Stiff neck
  • Sinus pain, ear pain, or headache

Fever is especially important because it’s often the first sign of an infection in people with cancer. Sometimes, fever is the only sign of an infection. Patients with neutropenia may not have other signs or symptoms of an infection, except for fever. You should have a thermometer to check your temperature – you can’t rely on how you feel to know when you have a fever. Patients may be told to call their doctor or nurse if they have a fever, or if they have other signs and symptoms of infection. Don’t take medicines to reduce your fever without checking with your doctor first. Ask your doctor what you should do and when you should call. Be sure you know how to reach your health care team after hours, including nights and weekends.

Key things you need to know

It’s important for people with cancer and their families and friends to know these things:

  • Your risk for infection
  • How long your immune system is likely be weak after treatment
  • How to take your temperature the right way, when to check it, and how often to check it
  • When to report a fever or other signs and symptoms of infection to the doctor or nurse
  • The importance of hand washing and hygiene for the patient and the people they come in contact with
  • How to take good care of your mouth and check for sores and signs of infection
  • How to clean cuts, scrapes, or other breaks in the skin and keep them clean to help prevent infection
  • The importance of cleaning around the anus after each bowel movement, using moist towelettes or baby wipes
  • Good care of IVs and central venous catheters (CVCs, like ports and PICC lines)
  • Where to look for signs of infection (skin, mouth, and CVC sites)
  • The importance of good nutrition, a balanced diet, and drinking plenty of fluids
  • The importance of sleep and exercise
  • The need to take medicines as prescribed
  • That the doctor knows about all medicines you’re taking (prescription, over-the-counter, vitamins, herbs, and supplements) – keep a list and update it at each doctor visit
  • Ways to prevent dryness of the skin and mucous membranes
  • The importance of talking with your health care team or doctor before getting vaccinated (immunized) and before getting close to children or adults who have recently had vaccinations.

Review these points with your cancer care team before and during treatment to get the information you need. Double check with them on how you should handle these things and find out if there are any special steps you should take during cancer treatment.

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.

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.

Cancer.Net. Infection. 2018. Accessed at on August 21, 2019.

Center for Disease Control and Prevention (CDC). Information for patients: Fight the bite. Accessed at on November 16, 2023.

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.

Kapadia RK, Staples JE, Gill CM, Fischer M, Khan E et al. Severe arboviral neuroinvasive disease in patients on rituximab therapy: A review. Clinical Infectious Diseases. 2023;76(6):1142-1148. Accessed at on November 16, 2023.

National Cancer Institute (NIH). Infection and neutropenia during cancer Treatment. 2018. Accessed at on August 16, 2019.

National Comprehensive Cancer Network (NCCN). Prevention and treatment of cancer-related infections. 2018. Version 1.2019. Accessed at 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.

Taplitz RA, Kennedy EB, Bow EJ, Crews J, Gleason C, Hawley DK, Langston AA, Nastoupil LJ, Rajotte M, Rolston K, Strasfield L, Flowers CR. Outpatient management of fever and neutropenia in adults treated for malignancy: American Society of Clinical Oncology and Infectious Diseases Society of America Clinical Practice Guideline Update. Journal of Clinical Oncology. 2018; 36(14):1443-1454.

Last Revised: November 16, 2023

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