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"By denying scientific principles, one may maintain any paradox." – Galileo Galilei


For years, the International Agency for Research on Cancer (IARC) has confused the public with hazard assessments that do not take into account exposure or real world scenarios. Since 1971, IARC has evaluated 998 agents and determined only one was “probably not” likely to cause cancer in humans.


What is IARC

IARC was established on May 20, 1965, through a resolution of the 18th World Health Assembly. Headquartered in Lyon, France, IARC is a functionally independent agency that is affiliated with the World Health Organization (WHO) of the United Nations (UN). IARC periodically emphasizes its position as a WHO affiliate, presumably to benefit from the credibility and authority that come with the WHO name. However, WHO has little actual oversight of IARC’s activities and in the past, has distanced itself from IARC’s cancer hazard assessments, known as monographs. IARC’s stated mission is “cancer research for cancer prevention” and objective is “to promote international collaboration in cancer research.”


IARC Monographs

IARC is best known for its series of Monographs on the carcinogenic hazards of various chemicals, mixtures, activities and agents, which it started producing in 1971.

  • What is a monograph?
    IARC monographs categorize environmental factors, including chemicals, complex mixtures, occupational exposures, physical agents, biological agents, and lifestyle factors that might pose a cancer hazard under any circumstances. The IARC monographs do not include new research; rather, they draw from existing research on the carcinogenicity of agents and chemicals.
  • How are they developed?
    Working groups of hand-picked scientists review publicly available studies[1] and evaluate if an exposure can be associated with cancer. They begin reviewing materials six months before meeting formally.IARC requires working group members to sign a confidentiality agreement not to disclose information “which IARC/WHO considers to be proprietary to itself or to parties collaborating with it.” Monograph authors must also explicitly agree that IARC has the “right to revise [their] work, to use it in a different manner from that originally envisaged, or not to use or publish it at all.”


IARC Monographs Evaluate Hazard, not Risk.

IARC’s work is focused exclusively on assessing the cancer hazard of a substance or action. It does not evaluate or determine cancer risk. This distinction often confuses the public because IARC uses the word “risk” in its monograph titles,[2] but its monographs preamble states the actual aim is to “identify cancer hazards even when risks are very low at current exposure levels.”[3]

This distinction makes a difference. An activity or exposure is considered a cancer hazard if it can potentially cause cancer under some possible set of circumstances. However, the activity or exposure also must be evaluated based on the cancer risk it poses to determine how likely it is that exposure to a substance or action will cause harm.

Unlike a simple hazard analysis, a risk assessment takes into account factors such as dose/concentration, exposure pathways, and probability of exposure to determine the likelihood that any given hazard will actually cause harm. Therefore, evaluations of cancer risks are far more relevant to policymakers and the public than IARC-reviewed cancer hazards.


IARC Monograph Classification System

IARC Monographs have assessed 998 substances since 1971, and only one has been determined “probably not” likely to cause cancer in humans, while the rest were identified as a possible, probable, or certain carcinogen.


[1] IARC evaluations rely only on studies that are in the public domain. Therefore, its findings do not reflect the vast amounts of data available to regulatory agencies, such as the U.S. Environmental Protection Agency (EPA) and European Food Safety Authority (EFSA), as they are considered proprietary in nature.

[2] “IARC Monographs on the Evaluation of Carcinogenic Risks to Humans.”

[3] A 2005 IARC advisory group debated whether to include risk assessment in their work, but decided it would require a “significant commitment of resources” and declined.