Cancer isn’t a sickness that you can “catch.” This is because a healthy immune system immediately identifies cancerous cells and gets rid of them before they can grow and spread.

There is some evidence that cancer can be spread through organ transplants if your immune system is weak. Also, your risk of developing certain cancers can increase if you’re exposed to infectious bacteria or viruses like human papillomavirus (HPV), which are contagious.

But in general, you can’t get cancer from another person or pass it on to someone else. Let’s get into the details about why cancer typically can’t be spread and the very small number of cases in which your risk can be increased.

The simplest answer here? No, you can’t catch cancer.

Unlike other contagious bacterial or viral conditions, cancer can’t be spread in any of the following ways:

  • kissing or exchanging spit in some way, such as by sharing utensils or a toothbrush
  • having sex, either protected or unprotected
  • coming into contact with the blood of someone who has cancer
  • touching the skin of someone with skin cancer
  • sharing a toilet seat with someone who has cancer
  • breathing in air that someone with cancer has breathed out

Cancer happens because of damage or mutations in the DNA that makes up otherwise healthy cells.

Over time, the healthy cells die off and are replaced with damaged DNA. These damaged cells multiply and eventually cause the growth of cancerous tissue around the area, which can then spread to other parts of your body (known as metastatic cancer).

If already cancerous cells get into the body of someone with a healthy immune system, the immune system is in a much better position to fight off and destroy the cancerous cells before they can grow and spread.

Cancer isn’t contagious like a typical infectious disease, but your parents can pass down genes that may increase your risk of developing certain types of cancer, which are called hereditary cancers.

These genes include:

  • Tumor suppressor genes. These genes are responsible for keeping cells from growing out of control. If they mutate, they can cause tumors to form. Examples include p53, Rb, and APC.
  • DNA repair genes. These genes help correct DNA mistakes before cells divide. If these genes mutate, they can’t prevent DNA mistakes from spreading, allowing cancerous cells to develop and grow out of control. Examples include BRCA1 and BRCA2.

Keep in mind that having these genes doesn’t mean you’re sure to get cancer at some point in your life. Like many other genes, these genes are affected by various factors, such as your diet or environment, that influence whether you get cancer.

The chances of passing cancer to your child at birth are very low. Even having cancer while pregnant is a rare occurrence in itself — it only happens in about 1 of every 1,000 pregnancies.

Cancer can be spread to the placenta while your baby’s in the womb, but research finds this to be extremely rare.

Here’s one case where cancer was spread from mother to child: In 2009, a woman in Japan with acute lymphoblastic leukemia (ALL) passed cancerous cells to her unborn child through the placenta.

The woman died shortly after the birth due to complications from ALL, and the baby was born with no signs of her mother’s cancer, as doctors expected.

But after 11 months, doctors discovered that the baby had inherited a mutation in her BCR-ABL1 gene from her mother. This caused the baby’s immune system not to recognize that the cells were cancerous and fight them off, and she eventually developed cancerous tumors.

Again, this is an extremely unique case linking a woman’s cancer with a specific gene mutation that allowed it to spread from mother to daughter. Cases like this are very rare.

Some infectious conditions can increase your risk of developing cancer. If you contract an infection from with an individual harboring certain viruses or bacteria, your cancer risk increases.

Here are some infectious conditions that have been shown to increase certain cancer risks:

Getting cancer from an organ transplant is rare. It only happens in about 2 of every 10,000 transplants. And many precautions are taken before transplanting an organ. This includes making sure that the donor doesn’t have cancer or a family history of cancer.

In cases where this does happen, it’s usually because of two main factors:

  • Your immune system is suppressed by medications meant to keep your body from rejecting the new organ as if it’s a foreign object.
  • You’re already at risk for developing cancer, especially skin cancer or kidney cancer.

You can’t get cancer from someone who has it.

If you do have cancer, it’s important to have a strong support system. Having a strong network of friends and family around can help you maintain a good quality of life.