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What is a Carcinogen?




Can bacon really cause cancer? What about paint? Alcohol? What is a carcinogen, anyway?

Cancer happens due to either DNA changes a person inherited from their parents or DNA changes that occur after they’re born—essentially a question of nature and nurture. Many things that can cause cancer via DNA changes during a person’s life. Researchers and doctors tend to categorize them into a few groups:

  • Radiation
  • Viruses
  • Obesity
  • Hormones
  • Physical inactivity
  • Chronic inflammation
  • Carcinogens

 Nature and Nurture Pull QuoteA carcinogen is usually defined as a chemical or other exposure that can lead to cancer. Well known examples are tobacco and UV light. There are several agencies involved in research of carcinogens: the International Agency for Research on Cancer, the U.S. National Toxicology Program, the U.S. Environmental Protection Agency (EPA), the CDC, the FDA, the National Cancer Institute, and the California Environmental Protection Agency.

Most of these agencies test chemicals on cells in petri dishes or on lab animals, because testing them on humans is unethical. Some research can be done to evaluate whether people who were exposed to a chemical during the normal course of their lives later developed cancer—for example a study could work to find out whether people who worked at ski resorts were more likely to develop cancer than their same-age peers working in an industry with less sun exposure. The information gleaned from these studies, when taken together, helps scientists make recommendations as to what chemicals may cause cancer in humans. Often, the chemicals are then ranked as to how confident scientists are in that recommendation.



Chemicals classified as "known human carcinogens" that you may recognize:

  • Acetaldehyde (a chemical in alcoholic beverages)
  • Alcoholic beverages
  • Arsenic
  • All forms of asbestos and everything that contains asbestos (including talc, which was found in some types of baby powder until the 1970s)
  • Emissions from the burning of coal, as well as coal tar
  • Diesel engine exhaust
  • Ethanol in alcoholic beverages
  • Hepatitus B and C viruses
  • Human papilloma virus (HPV)
  • Leather dust
  • Untreated or mildly treated mineral oils
  • Nickel metal compounds
  • Eating processed meats
  • Radium (which was used to make clock faces glow in the dark until the 1960s)
  • Inhalation of soot
  • Tobacco (both smoked and smokeless, as well as firsthand or secondhand)
  • Wood dust


Chemicals classified as "probable carcinogens" that you may recognize:

  • Art glass
  • Emissions from the burning of biomass fuels like wood and animal dung
  • Workplace exposures for those who work as barbers or hairdressers
  • Emissions from high-temperature frying
  • Lead compounds
  • Consumption of red meat


Some agencies may disagree on the level of confidence with which they call a chemical a carcinogen. For instance, the National Toxicology Program says they “reasonably expect” acetaldehyde to be a carcinogen, while the International Agency for Research on Cancer calls it a known human carcinogen.

Having said all that, a single exposure to any one carcinogen doesn’t guarantee that a person will have cancer. The American Cancer Society says, “Carcinogens do not cause cancer at all times, under all circumstance. Some may only be carcinogenic if a person is exposed in a certain way (for example, swallowing it as opposed to touching it). Some may only cause cancer in people who have a certain genetic makeup. Some of these agents may lead to cancer after only a very small exposure, while others might require intense exposure over many years.”

 Carcinogen Pull QuoteAdditionally, even though two carcinogens might both be classified as known carcinogens, one may lead to cancer more often than another. For instance, smoking tobacco is more likely to cause cancer than eating processed meat. They’re grouped in the same category (known human carcinogen) because the evidence that both cause cancer is very strong, not because they’re equally risky.

The American Cancer Society explains, “Even if a substance or exposure is known or suspected to cause cancer, this does not necessarily mean that it can or should be avoided at all costs. For example, estrogen is a known carcinogen that occurs naturally in the body. Exposure to ultraviolet (UV) radiation from sunlight is also known to cause cancer, but it’s not practical (or advisable) to completely avoid the sun.”

So, yes, bacon can probably cause cancer, along with paint and alcohol. But these things are associated with very different levels of risk. The American Cancer Association says, if you’re concerned about something, you should probably speak with your doctor so they can help you evaluate the risks.


Cancer. (2018, March 09). Retrieved from https://www.mayoclinic.org/diseases-conditions/cancer/symptoms-causes/syc-20370588

Known and Probable Human Carcinogens. (n.d.). Retrieved from https://www.cancer.org/cancer/cancer-causes/general-info/known-and-probable-human-carcinogens.html

Talcum Powder and Cancer. (n.d.). Retrieved from https://www.cancer.org/cancer/cancer-causes/talcum-powder-and-cancer.html


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