Graphic illustration with gradient background showing the text “Class 2B Possible Human Carcinogens,” highlighting IARC’s Group 2B classification of agents that are possibly carcinogenic to humans.
Published: 26 February 2026
By EMFSA
Class 2B Possible Human Carcinogens
Class 2B Possible Human Carcinogens are substances or exposures identified by the International Agency for Research on Cancer (IARC) as possibly carcinogenic to humans. This classification is based on limited or inconclusive evidence in humans, supported by preclinical studies in animals or mechanistic research. Importantly, being classified as possibly carcinogenic indicates hazard, not proven risk at typical environmental exposure levels.
Evidence and Examples of Class 2B Agents
To illustrate the diversity of evidence, consider two notable examples. In November 2025, IARC classified vinclozolin, a pesticide, as “possibly carcinogenic to humans,” based on animal studies showing liver and reproductive effects, including multigenerational impacts. Human data remain limited, but the experimental findings were sufficient to support a Group 2B designation.
Radiofrequency (RF) electromagnetic fields were classified earlier, in 2011, based primarily on limited human epidemiological evidence suggesting a potential association with certain brain tumors, alongside mechanistic data from preclinical studies available at that time. Following this classification, additional research, such as the NTP 2018 animal study, investigated high-dose RF-EMF exposure in both rats and mice and observed small increases in certain tumors in male rats, particularly cardiac schwannomas and some brain gliomas. Although these post-classification studies contribute to ongoing research, they did not influence the original Group 2B designation. Evaluations by the WHO EMF Project and IARC continue to assess new evidence to determine whether future reclassification may be warranted.
At the same time, international review efforts have continued. The WHO EMF Project and IARC are assessing newer evidence to determine whether the existing classification remains appropriate or whether future reassessment may be warranted.
Taken together, these examples show that Class 2B agents represent signals of potential carcinogenicity that warrant further research, regulatory attention, and precautionary measures, while reinforcing that current evidence in humans remains limited or inconclusive.
Regulatory and Precautionary Approaches
Regulatory responses vary depending on the type of agent and the strength of evidence available. In some jurisdictions, vinclozolin has been restricted or phased out following toxicological concerns. By contrast, regulators manage RF-EMF exposure primarily through guidelines and public health recommendations.
It is important to clarify that the World Health Organization does not set exposure limits directly. Instead, independent scientific bodies such as ICNIRP and IEEE develop exposure guidelines, while WHO evaluates the broader health evidence and provides risk assessments to governments.
Understanding Class 2B Possible Human Carcinogens
Overall, Class 2B Possible Human Carcinogens indicate that credible scientific signals exist, yet the evidence is not strong enough to establish causation in humans. As a result, the designation encourages further research, careful monitoring, and proportionate precaution, without implying confirmed human cancer risk.
IARC Classification System
The International Agency for Research on Cancer classification system is defined as follows:
- Group 1 — Carcinogenic to humans
- Group 2A — Probably carcinogenic to humans
- Group 2B — Possibly carcinogenic to humans
- Group 3 — Not classifiable as to carcinogenicity in humans
More on the topic: : IARC Monographs evaluation of the carcinogenicity of night shift work https://www.emfsa.co.za/research-and-studies/iarc-monographs-evaluation-of-the-carcinogenicity-of-night-shift-work/
References:
- International Agency for Research on Cancer (IARC). List of Classifications, including Radiofrequency Electromagnetic Fields. Last updated 25 February 2026.https://monographs.iarc.who.int/list-of-classifications
- US Right to Know. One Exposure, Twenty Generations Later: The Damage is Unfolding. 2025. https://usrtk.org/healthwire/one-exposure-twenty-generations-later-the-damage-is-unfolding/
- World Health Organization. International EMF Project https://www.who.int/initiatives/the-international-emf-project
- WHO Radiation and health https://www.who.int/teams/environment-climate-change-and-health/radiation-and-health/non-ionizing/wireless
- ICNIRP. Guidelines for limiting exposure to electromagnetic fields (100 kHz – 300 GHz). 2020. https://www.icnirp.org/en/publications/article/rf-guidelines-2020.html
* Image adapted from Photo by Milad Fakurian on Unsplash
