Is Cancer Contagious?

A Common Question With Uncommon Considerations

Cancer is not contagious. It cannot be transmitted from one person to another by breathing the same air, sharing a toothbrush, touching, kissing, or having sex. With a few rare exceptions—such as organ transplant recipients and mother-to-fetal transmission—the immune system will recognize and destroy any foreign cells that get into the body, including cancer cells from another person.

Though cancer is not contagious, some infections that are contagious can increase a person's risk of developing cancer. Cancer may run in families, but instead of being transmitted, this risk is related to genetics or common exposures that increase risk.

This article will cover why cancer isn't contagious, and the stigma people with cancer face because of the misinformation. 

Mature ethnic woman with cancer wearing headwrap on couch
FatCamera / Getty Images

Why Cancer Is Not Contagious

Cancer cells aren't contagious in humans. That's because they can't live outside the body, and the immune system recognizes cancer cells entering the body.

What Does Cancer Spreading Mean?

Cancer does not spread from person to person. "Cancer spreading" describes metastasis, when cancer moves from the primary location to a new location in the body. This can occur through the lymphatic system, the bloodstream, or growing into surrounding tissues.

In an unethical experiement conducted in the 1950s and 1960s, a researcher and physician named Dr. Chester Southam injected live cancer cells into people to see if he could "cause" cancer. The people did not know that they had been given cancer cells. With only one exception, the immune systems of the people in the experiment fought off the cancer cells before they got beyond the nodule stage.

Our immune cells see cancer cells from another person as they would see disease-causing viruses or bacteria. The fact that cancer isn't contagious is better understood when looking at how cancer develops.

Why Cancer Happens

Cells normally grow and divide to keep the body’s organs working. When old ones die, new ones replace them. 

With cancer, the body's cells start to change, divide, and multiply out of control. This happens when there is damage, or a mutation, to the DNA in the cells. The cell makes copies of itself that are abnormal and starts to invade tissues in the body.

These cell mutations can happen because of lifestyle factors like UV sun exposure or smoking. Genetic mutations can also be inherited.

Cancer Clusters

Sometimes, cancer cases seem to “cluster” in an area, which can make it seem as though people are “catching” it from each other. The truth is that cancer clusters are more likely related to shared risk factors, such as something in the environment, that all the people diagnosed with cancer have in common.

Cancer Risk in Families

Genetics plays a role in cancers that seem to “run in families.” Even when cancer is found in multiple members of a family, it does not mean that cancer is being passed from one person to another like a contagious illness. Instead, it may have to do with genes that are passed down in a family. 

However, having a genetic predisposition to cancer does not mean that a person will get cancer. Hereditary cancer accounts for about 10% of cancers overall. The influence of genetics can vary by cancer type. 

Many gene mutations associated with cancer (such as BRCA) occur in tumor suppressor genes. These genes code for proteins that fix damaged DNA or get rid of it before it can turn into cancer cells. 

Having a mutated gene does not cause cancer—rather, it gets in the way of the body's ability to repair damaged cells. Even without a genetic predisposition, cancer may seem to cluster in families for other reasons like shared lifestyle habits (like smoking or diet) and exposure to environmental carcinogens, such as radon exposure in the home. 

Cancers can also be related to exposure to the virus (like hepatitis B) that can be spread between family members.

Organ Transplants and Cancer Risk

If cancer cells from someone else's body got into your body, your immune system should be able to destroy them. However, there have been cases of cancer being transmitted from one person to another through organ transplants. It’s thought that transfusion-related cancer may occur in about 3 out of 5,000 transplant recipients.

With organ transplants, two factors contribute to the risk of cancer:

  • Instead of just a few cancer cells (such as with a needle stick), a large volume of tumor cells is implanted in a person (from a mass in the transplanted organ). 
  • People receiving organ transplants are usually severely immunocompromised because of the medications they have to take to prevent organ rejection.

Recent studies have shown that people who receive organ transplants are at a higher risk for certain cancers. For example, a 2022 study by researchers at the Mayo Clinic showed that organ transplant patients were at a significantly higher risk for skin cancer than the general population.

A 2022 study of patients in Finland found that solid organ transplant recipients had a higher risk for cancer than the general population, and were also more likely to die from cancer.

An older but larger study done in 2011 by researchers at the National Cancer Institute looked at more than 175,000 organ transplant recipients to see how many of them developed cancer. The study showed that the patients who got organ transplants were at a higher risk for 32 types of cancer compared to the general population, with the most common being non-Hodgkin lymphoma, lung cancer, liver cancer, and kidney cancer. 

However, the study also noted that the type of transplant a patient had was often linked to their cancer risk. For example, the risk for lung cancer was higher in people who had lung transplants, and the risk for liver cancer was higher in people who had liver transplants. All organ transplant recipients in the study had a higher risk for kidney cancer, regardless of what organ transplant they had received. 

Cancer and Blood Transfusions

There is no evidence of cancer being transmitted through a blood transfusion. However, there are limitations on when people with cancer can donate blood.

Cancer Transmission During Pregnancy

There are a few reported cases of cancer transmission during pregnancy. While rare, this transmission could happen in a few ways:

  • From the pregnant parent to the fetus. While tumors may spread to the placenta, the placenta usually prevents cancer cells from reaching the fetus. About 1 in 1,000 pregnant people are thought to have cancer. The chance of cancer being transmitted is estimated at only 0.000005%. When it does happen, cancer transmission is most common with leukemia/lymphomas and melanoma.
  • Twin-to-twin transmission of leukemia. It’s rare but might be possible for twins to transmit leukemia to one another in the womb.
  • Choriocarcinoma. Choriocarcinoma is a rare tumor of the placenta. The tumor may spread to both the pregnant parent and the fetus. This is the only case of serial transmission of cancer—that is, from the placenta to the pregnant person, and then from the pregnant person to recipients of organs donated by the pregnant person.

A pregnant person cannot transmit cancer by breastfeeding. However, if they are being treated for cancer, they may not be able to breastfeed because the medications could be passed to their baby through breast milk.

Infections That Increase Cancer Risk

Some infections that can be passed from person to person are thought to lead to cancer. However, when this happens, it's not cancer that’s contagious, but the infection that may or may not lead to cancer. 

In 2018, it's estimated that there were 2.2 million infection-attributable cancer cases diagnosed in the United States.

While infections that could be linked to cancer are common, it’s not common to get cancer from them. Most cancers have more than one cause. Other factors such as exposure to carcinogens, immunosuppression, genetics, and lifestyle can combine with an infection to lead to cancer. 

Infections may lead to cancer in different ways. For example, some infections cause inflammation that leads to cancer because there is an increase in the division of cells that are involved in repair. Other infections can cause immunosuppression that may contribute to cancer, or cause DNA damage and mutations linked to cancer.

Viruses associated with cancer include:

 Microbe Types of Cancer
Parasitic worms Bladder and bile duct cancer
Human papillomavirus (HPV) Cancers of the cervix, vagina, vulva, penis, anus, and some cancers of the head, and neck
Epstein-Barr virus (EBV) Nasopharyngeal cancer, lymphoma of the stomach, Hodgkin lymphoma, and Burkitt lymphoma
Hepatitis B virus (HBV) and hepatitis C virus (HCV) Liver cancer
Human herpes virus type 8 (HHV-8) Kaposi sarcoma (only with a weakened immune system)
Human T-lymphotropic virus-1 (HTLV-1) Adult T-cell leukemia/lymphoma (ATL)
Merkel cell polyomavirus Merkel cell carcinoma
Helicobacter pylori (H. pylori) Stomach cancer
Chlamydia trachomatis Cervical cancer
  • Human papillomavirus (HPV). HPV is the most common sexually transmitted infection (STI). It has been linked with cervical cancer, anal cancer, penile cancer, vaginal cancer, and head and neck cancers. In most cases, an HPV infection goes away on its own, but when it does not, it may lead to inflammation and cancer. However, not all strains of HPV are linked to cancer.
  • Hepatitis B and hepatitis C virus. Both hepatitis B and C are associated with liver cancer. They are the most significant cause of this type of cancer worldwide.
  • Epstein Barr virus (EBV). EBV is best known for causing mononucleosis, but it has been linked to several cancers including Burkitt's lymphoma, gastric carcinoma, Hodgkin lymphoma, and nasopharyngeal carcinoma. While 90%-95% of people are infected with EBV globally, only about 1% of them will develop cancer.
  • HIV/AIDS. Several types of cancer are associated with HIV/AIDS and are related to immunosuppression. Human herpesvirus Type 8 (HHV-8) or Kaposi sarcoma herpes virus may lead to Kaposi's sarcoma in people with HIV.
  • Human T-lymphotropic virus-1 (HTLV-1). HTLV-1 is associated with some leukemias and lymphomas, While the infection is relatively common, cancers from it are not.
  • Merkel cell polyomavirus. The Merkel cell polyomavirus is very common worldwide but rarely leads to a type of skin cancer called Merkel cell carcinoma.

Bacteria associated with cancer include:

Parasites associated with cancer include:

  • Liver flukes. Two different liver flukes are linked with bile duct cancer. They are found primarily in East Asia.
  • Schistosomiasis. The worm that causes this disease is also associated with bladder cancer.

In addition to these specific organisms, microorganisms on or in our bodies could be associated with an increased or decreased risk of cancer. For example, the normal bacteria of the skin (microbiome) might be related to the development of skin cancer. Also, having a balance of good gut bacteria may lower your risk of lymphoma.

Stigma Due to Myth That Cancer is Contagious

Cancer patients may face stigma because of the misbelief that cancer is contagious. If the people in a person’s life do not understand how cancer happens, they may avoid that person out of fear of “catching cancer.” People with cancer may also be left out or shamed by others if they are considered to be capable of spreading the disease to other people. 

Having cancer is a profoundly challenging and frightening experience and a person needs support from their loved ones. 

If friends, family, coworkers, and even strangers mistakenly believe that they will get cancer just from being around someone with it, a person who is trying to cope with the diagnosis and get through treatment may have to face that difficult time alone. 

Even if a person has cancer that may have been related to an infection that can be spread between people, it does not mean that they will give cancer—or even the infection—to another person. 

If you are trying to manage a cancer diagnosis and your loved ones do not understand, talk to your provider. They might be able to help your loved ones understand why cancer happens and show them that it is not contagious and that they do not have to worry about getting cancer just from being around you and supporting you. 

Summary

Cancer is not contagious. Cancer happens for more than one reason, like genes and environmental factors, that come together over a person’s lifetime. While certain infections can increase the chances of getting some kinds of cancer, it does not mean that cancer is contagious even if the infection is. 

If you have a loved one with cancer, know that you cannot catch cancer just from being around them. You can feel safe supporting them as they navigate the diagnosis and treatment. 

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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.
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Additional Reading
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By Blyss Splane
Blyss Splane is a certified operating room nurse working as a freelance content writer and former travel nurse. She works as a freelance content writer for healthcare blogs when she's not spending time with her husband and dog.

Originally written by Lisa Fayed