(Matt Rourke/Associated Press)

In the 45 years the World Health Organization's cancer research arm has been studying carcinogenic agents it's looked at nearly 1,000 things you might eat, be exposed to, or do that might put you at higher risk of getting cancer. They've determined that about half of them do cause cancer or "probably" or "possibly" cause it.

When it comes to business, public health and the environment, this cancer list is enormously influential. It affects everything from workplace safety to dietary guidelines and pollution controls around the world. But much of this debate has been happening behind the scenes and the WHO's International Agency for Research on Cancer was hardly a household name.

That changed on Monday when the IARC announced a shocker (at least for the average citizen) -- that it would be adding as a processed meats like hot dogs, sausages, bacon, ham and other processed meats to its list of highest risk carcinogens, causing furor and confusion among meat-loving folk all over the planet. The expert panel also declared red meat a probable carcinogen.

A new World Health Organization study found that processed meat like bacon and hot dogs cause cancer. It is the most prominent group to declare it a cause of the disease, and the U.S. beef industry isn't happy about it. (Jenny Starrs/The Washington Post)

[WHO says hot dogs, bacon cause cancer. Does this news mean people should become vegetarians?]

There may be other high-profile, controversial additions coming up as the IARC has announced it will investigate other food products in the near future.

Next up for study: coffee, which will be discussed at a meeting in late May 2016.

Below is a look at some of the other cancer-causing agents that have been added to the IARC growing list over the years. They include a slew of industrial chemicals you've probably never heard of as well as some ubiquitous and often unavoidable aspects of modern life: air pollution, tobacco smoking, alcohol, and X-rays.


The yellow leaves of a gingko tree hold to a branch in the Asian Collection at the U.S. National Arboretum. An extract made from the plant is marketed as a dietary supplement that can boost cognitive function, among other things. (Carolyn Kaster/Associated Press)

Group 1 - Carcinogenic:

This is the group for which there is the most evidence of cancer risk. But being in this group doesn't mean that the risk associated with each agent is the same -- for example, that the impact of smoking is the same as eating some bacon. There are about 120 agents listed.

  • Arsenic and arsenic compounds
  • Asbestos
  • Coal, indoor emissions; gasification; coal-tar distillation; coal-tar pitch
  • Viruses: Epstein-Barr, chronic infection with Hepatitis B or C, HIV type 1, HPV types 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59 and 66
  • Hormonal contraceptives containing both estrogen and progestogen; estrogens (both non steroidal and steroidal); estrogen therapy for postmenopausal women
  • Ethanol in alcoholic drinks
  • Formaldehyde
  • Herbal remedies containing plant species of the genus Aristolochia
  • Mustard gas (Sulfur mustard)
  • Radioactive substances: Plutonium-239 and its decay products, as aerosols; Radioiodines; Radium-224 and its decay products; Radium-226 and its decay products; Radium-228 and its decay products; Radon-222 and its decay products
  • Outdoor air pollution, as well as particulate matter
  • Solar radiation
  • Tamoxifen6
  • Tobacco, smoking, second-hand smoke
  • Ultraviolet radiation
  • X-Radiation and gamma radiation
  • Processed meat

Group 2A - Probably carcinogenic:

Limited evidence of carcinogenicity in humans, sufficient evidence of carcinogenicity in experimental animals. This group has about 75 agents.

  • Androgenic steroids (often used to stimulate muscle growth)
  • Glyphosate (contained in Roundup and other insecticides or herbicides)
  • Inorganic lead compounds
  • Occupational exposure as a hairdresser or in petroleum refining.
  • Shift work that disrupts sleep patterns
  • Red meat

Glass of whisky with ice. (iStock)

Group 2B - Possibly carcinogenic:

Limited evidence of carcinogenicity in humans, less than sufficient evidence of carcinogenicity in experimental animals. This group has nearly 300 agents.

  • Chloroform
  • Radiofrequency electromagnetic fields
  • Magenta dyes
  • Pickled vegetables
  • Gingko biloba extract
  • Welding fumes
  • Carpentry and joinery
  • Dry cleaning, occupational exposure
  • Firefighting, occupational exposure

[Bacon, hot dogs cause cancer, World Health Organization says]

Group 3 - Not classifiable:

By far the largest group with more than 510 substances or exposure risks.

Group 4 - Probably not carcinogenic:

There's only one agent in this group -- caprolactam, a chemical used in the production of a type of nylon.

Read more:

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