Carcinogens are substances that may increase your risk of cancer. There are more than 100 known carcinogens. Carcinogens may be physical, such as ultraviolet rays from the sun; chemical, like asbestos; or biological, such as infections caused by certain viruses. Simply having contact with a carcinogen doesn’t mean you’ll develop cancer.

What are carcinogens?

Carcinogens (pronounced “kahr-sin-o-jens”) are substances that may increase your risk of developing cancer. Experts have identified more than 100 carcinogens. Carcinogens may be physical, such as ultraviolet rays from the sun; chemical, like asbestos; or biological, such as infections caused by certain viruses. Simply having contact with a carcinogen doesn’t mean you’ll develop cancer. While you may not be able to avoid some carcinogens, there are steps you can take to reduce your risk of developing cancer from carcinogen exposure.


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How do carcinogens cause cancer?

To understand how carcinogens cause cancer, it may help to know more about the relationship between carcinogens and your genetic makeup.

Your DNA is in your genes. Your genes contain instruction manuals for making proteins. Proteins control millions of actions, including how cells grow and multiply. When a carcinogen changes your DNA, it triggers a chain reaction that turns normal cells into cancerous cells.

Sometimes, carcinogens do direct damage to your DNA so it stops working as it should. Other times, cells that typically repair DNA damage from carcinogens can’t take care of the issue. Left unrepaired, damaged DNA may lead to changes (mutations) in certain genes.

Depending on the specific mutation or change, your genes may start giving cells instructions to multiply uncontrollably, becoming cancerous tumors or blood cancer. But cancer doesn’t develop right away. Carcinogens build up over time. It may take years before a carcinogen in your body begins the chain reaction that leads to cancer.

How would I have contact with a carcinogen?

You may have contact with a carcinogen if:

  • You have certain lifestyle habits such as using tobacco.
  • You spend time in a workplace that uses carcinogenic chemicals to make products.
  • You have certain viruses, like human papillomavirus (HPV), that cause cancer.

Again, simply having contact with a carcinogen doesn’t mean you’ll develop cancer. Factors that increase cancer risk include:

  • Longtime exposure to a carcinogen. For example, someone who uses tobacco, has used tobacco for many years or is exposed to second-hand smoke is more likely to have cancer than someone who’s never used tobacco, quit using tobacco and avoids second-hand smoke.
  • Extensive exposure to a carcinogen.For example, drinking significant amounts of beverages containing alcohol increases your cancer risk. According to the American Cancer Society, men and people assigned male at birth (AMAB) should limit their intake to two drinks a day. Women and people assigned female at birth (AFAB) should limit intake to one drink a day.
  • Genetic (inherited) mutations. About 5% to 12% of cancers are inherited, meaning people are born with genetic mutations that cause cancer. Someone who has an inherited cancer and is exposed to carcinogens has an increased risk of developing cancer.

Who decides if something is a carcinogen?

In the United States, the National Toxicology Program (NTP) evaluates research and publishes lists of known and possible carcinogens. The International Agency for Research on Cancer (IARC) also evaluates research and publishes its findings.

In general, both agencies rely on laboratory tests and epidemiology research (studies in people) to determine if a substance is a carcinogen.

The most recent NTP report lists 63 carcinogenic substances. The report also lists 193 substances that may cause cancer. The most recent IARC research lists 122 substances known to cause cancer, 93 substances that probably cause cancer and 319 substances that may cause cancer.

What are types of carcinogens?

The IARC has three categories of carcinogens:

  • Physical carcinogens, like ultraviolet rays from the sun and ionizing radiation from sources like radon in homes or X-rays and other medical imaging tests.
  • Chemical carcinogens, like asbestos, tobacco smoke, beverages containing alcohol, aflatoxin (a fungus that contaminates food) and arsenic that appears naturally in the air, water and soil.
  • Biological carcinogens, such as infections from certain viruses, bacteria or parasites.
What are common carcinogens?

Some common carcinogens include:

  • Beverages containing alcohol. The NTP lists alcohol as a known carcinogen. Studies show the more alcohol you consume, the higher your chance of developing several different kinds of cancer, including head and neck cancer, liver cancer and esophageal cancer.
  • Tobacco products, including smokeless tobacco and second-hand smoke. Tobacco use is the leading cause of cancer in the United States.
  • Ultraviolet rays from the sun or from radiation therapy may cause skin cancer.
  • Radon. This is a colorless, odorless gas. You may be exposed to radon when you’re inside buildings like businesses, schools or even your own home. Radon is the second leading cause of lung cancer.
  • Asbestos. Asbestos once was a common form of insulation. You may be exposed to asbestos if you spend time in buildings constructed before 1989, when the U.S. Environmental Protection Agency (EPA) banned all new uses of asbestos. Asbestos is linked to malignant (cancerous) mesothelioma, lung cancer, laryngeal cancer and ovarian cancer.
  • Formaldehyde. Studies suggest people exposed to high levels of formaldehyde in the workplace have an increased risk of acute myeloid leukemia and rare cancers in their nasal cavities and sinuses.
  • Processed meat. Meat that’s been transformed by salting, curing or smoking is linked to colorectal cancer.

How can I reduce my exposure to carcinogens?

Unfortunately, you can’t avoid all carcinogens. But you can avoid some known carcinogens by:

  • Not using tobacco.
  • Avoiding beverages containing alcohol.
  • Getting vaccinated against viruses that are considered carcinogens.
  • Protecting your skin from the sun and other sources of ultraviolet radiation.
When should I talk to a healthcare provider about my carcinogen risk?

You may want to talk to a provider if you use tobacco or regularly drink beverages containing alcohol. Providers may recommend programs to help you quit smoking. They may recommend you cut back on the amount of beverages with alcohol that you drink.

You may want to ask a provider about your lifetime risk of developing cancer. (The National Cancer Institute publishes lifetime risk data.) If you have an increased lifetime risk of a certain cancer, you may want to avoid carcinogens linked to that type of cancer.

Depending on your situation, a provider may recommend you have specific cancer screening tests.

A note from Cleveland Clinic

Carcinogens are substances that can cause cancer. There are more than 100 known carcinogens. You may encounter carcinogens in your daily life. For example, there may be tiny amounts of arsenic in drinking water. Ultraviolet rays from the sun are carcinogens. There may be carcinogenic chemicals in your home or workplace.

You may worry that you don’t know enough to decide if you’re at risk. That’s understandable. But research shows the carcinogens mostly likely to cause cancer involve common lifestyle activities you can manage. For example, tobacco is a known carcinogen linked to several cancers. You can reduce your risk by quitting tobacco.

If you’re concerned about carcinogen exposure, talk to a healthcare provider. They’ll evaluate your overall situation and provide perspective on your personal risk of cancer from carcinogens. Knowledge is power. Knowing your risk and how to reduce it will help you manage your overall health. More than that, it may give you peace of mind.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 06/19/2023.

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