What do a cell phone and a career as a hairdresser have in common? Both could possibly be carinogenic (or cause cancer), according to the International Agency for Research on Cancer (IARC).
It’s no wonder why IARC classifications cause hysteria. IARC’s purpose is to determine if specific agents could cause cancer in humans, not to communicate the nuances of their classifications. So, let’s figure out how these analyses work and what they mean.
What is IARC?
IARC, the International Agency for Research on Cancer headquartered in Lyon, France, operates under the auspices of the World Health Organization. IARC convenes groups of scientists from around the globe three times a year, and these Working Groups evaluate the weight of the evidence that an agent, chemical compound, complex mixtures (including individual foods), occupational exposures, physical and biological agents and lifestyle factors, can influence the risk of cancer in humans.
How does IARC classify compounds with respect to their cancer risk?
IARC classifies compounds into four groups based on the available scientific evidence for increasing cancer risk in animals and humans. In 2019, IARC revised its classifications. The four classifications are Groups 1, 2A, 2B and 3. For definitions of these groups, please see the Preamble.
| Classification | Definition | Real life example |
| Group 1 | Carcinogenic to humans | Sunlight; outdoor air pollution; wood dust |
| Group 2A | Probably carcinogenic to humans | Diesel engine exhaust; working as a barber/hairdresser; night shift work |
| Group 2B | Possibly carcinogenic to humans | Gasoline exhaust; aloe vera |
| Group 3 | Not classifiable as to its carcinogenicity to humans | Caffeine; hair coloring products; fluorescent lighting; coffee |
For more information on IARC methods and classifications, please see the IARC Preamble.
How many compounds have received a classification from IARC?
Of the more than 900 substances classified by IARC to date, only one chemical compound has been classified as Group 4 (probably not carcinogenic to humans). Over 500 substances have been classified as Group 3 (not classifiable as to its carcinogenicity), and over 400 have received a classification of Group 2B or higher. For a complete list of IARC classifications, please see Agents Classified by the IARC Monographs.
Are there compounds present in foods that have been classified as Group 2B or higher by IARC?
Yes, compounds present in foods have been given a Group 2B or higher classification by IARC. Coffee itself was classified in Group 2B based on limited evidence in humans in 1990, although there is now evidence that coffee can actually reduce the risk of cancer. Other compounds in foods that are classified by IARC include acrylamide (Group 2A) and furan (Group 2B) that are formed naturally in food as part of normal cooking processes. Acetaldehyde and caffeic acid are also Group 2B compounds that occur naturally in foods such as fruits and coffee.
What does a classification of Group 2B mean?
IARC defines a Group 2B classification as “the agent is possibly carcinogenic to humans.” This category is used by IARC when there is only limited scientific evidence in human studies that a compound increases cancer risk in humans and when there is sufficient evidence of an increased cancer risk in experimental animals. IARC also uses information on biological mechanisms to alter the determination of final classifications.
Does this mean that consumption of food containing those compounds classified as Group 2B and above will cause cancer in humans?
No, the IARC classification is a Hazard Identification determination only, the first step in the risk assessment process. IARC does not engage in risk assessments, so the IARC classifications do not mean that consuming a food containing those compounds will cause cancer in humans.
