IARC Group 2B: what "possibly carcinogenic to humans" means
Last reviewed: 20 October 2026
The short answer: Group 2B is the label the International Agency for Research on Cancer (IARC) gives agents whose evidence of causing cancer is limited — a possible association shows up in human or animal studies, but chance, bias or confounding cannot be ruled out. IARC classified radiofrequency electromagnetic fields (the band used by mobile phones and WiFi) as Group 2B in 2011, and extremely low frequency (ELF) magnetic fields (the band of power lines and household wiring) as Group 2B in 2002. Both classifications are statements about the strength of the evidence — not about how large a risk might be, and not exposure limits (IARC Monographs Vol. 80, 2002; Vol. 102, evaluation May 2011, volume published 2013; IARC press release No. 208, 31 May 2011). This page explains what the classification is built from and what it does and does not say.
What IARC is and how the Monographs classify
IARC is the World Health Organization's cancer research agency, based in Lyon, France. Its Monographs programme convenes working groups of scientists who review all the available evidence on an agent — human studies, animal studies and mechanistic data — and assign it to one of five categories: Group 1 (carcinogenic to humans), Group 2A (probably carcinogenic), Group 2B (possibly carcinogenic), Group 3 (not classifiable) and Group 4 (probably not carcinogenic) (IARC Preamble, 2006).
Two properties of the scheme matter for reading it correctly. First, it is hazard identification: the question is whether an agent can cause cancer in some circumstance, not how much risk a given exposure level carries (IARC Preamble, 2006). Second, the groups grade evidence strength, not danger — an agent can sit in Group 2B because the evidence is thin, while another Group 2B agent with stronger evidence has moved up. Group 2B historically contains a wide range of everyday agents — aloe vera whole-leaf extract, Asian-style pickled vegetables and bracken fern among them (IARC Monographs) — and coffee was Group 2B from 1991 until a 2016 re-review moved it to Group 3 as better evidence accumulated (IARC, 2016).
The two electromagnetic classifications, dated
| Exposure | Classification | Evidence basis, as published |
|---|---|---|
| ELF magnetic fields (50/60 Hz) | Group 2B, 2002 | Limited evidence from human epidemiology: the statistical association between long-term average residential magnetic fields above roughly 0.3–0.4 µT and childhood leukaemia. Animal data judged inadequate; ELF electric fields and static fields were placed in Group 3 (IARC Monographs Vol. 80, 2002). |
| Radiofrequency electromagnetic fields | Group 2B, 2011 | Limited evidence of glioma (a brain cancer) among the heaviest mobile-phone users in human observational studies — chiefly the INTERPHONE study and a Swedish pooled analysis — with evidence in animals judged inadequate (Baan et al., The Lancet Oncology 12(7): 624–626, 2011; IARC Monographs Vol. 102). |
What Group 2B does not mean
- It is not a measure of risk size. "Possibly carcinogenic" says nothing about how strong an effect might be or at what exposure level it would appear — hazard classification and risk assessment are different exercises (IARC Preamble, 2006).
- It is not proof of causation. Limited evidence means a real association cannot be excluded — and cannot be confirmed; biases in phone-use epidemiology, for example, were why the INTERPHONE authors declined a causal reading of their own finding (INTERPHONE Study Group, International Journal of Epidemiology 39(3): 675–694, 2010).
- It is not an exposure limit. The numerical limits this site's calculator compares against — the ICNIRP 2010 and ICNIRP 2020 reference levels and similar national figures — are set against established acute effects with built-in safety margins; they answer a different question from a hazard classification, which is why a Group 2B agent can exist at exposures far below any limit.
- It is not necessarily permanent. IARC re-reviews agents as evidence accumulates — coffee's move from Group 2B to Group 3 in 2016 is the standard example (IARC, 2016). Since the 2011 RF classification, a WHO-commissioned systematic review of human studies found no association between mobile-phone use and brain cancer (Karipidis et al., Environment International, 2024); IARC classifications are revisited as this body of work grows.
How this site uses the IARC classifications
- The calculator compares modelled exposures against guideline reference levels, never against hazard classifications — see the calculator standards comparison for how each band's figure is sourced.
- Per-source pages cite the classifications where the evidence behind them lives: mobile phones (RF, 2011) and power lines (ELF magnetic fields, 2002).
- The 0.3–0.4 µT epidemiology band behind the 2002 ELF classification is also the anchor for the calculator's stricter precautionary power-frequency options — explained on the standards comparison page.
Sources
Every classification and claim on this page carries its dated source:
- IARC (2002), "Non-ionizing radiation, Part 1: static and extremely low-frequency (ELF) electric and magnetic fields", IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol. 80 — ELF magnetic fields classified Group 2B.
- IARC (2013), "Non-ionizing radiation, Part 2: radiofrequency electromagnetic fields", IARC Monographs, Vol. 102 — RF classified Group 2B by the working group that met 24–31 May 2011; announced in IARC press release No. 208 (31 May 2011) and summarized in Baan et al., The Lancet Oncology 12(7): 624–626 (2011).
- IARC (2006), "Preamble to the IARC Monographs on the Evaluation of Carcinogenic Risks to Humans" — the hazard-identification categories and the meaning of "limited evidence".
- IARC (2016), re-evaluation of coffee drinking (Monographs Vol. 114 evaluation, June 2016) — coffee moved from Group 2B (1991) to Group 3.
- WHO (2007), "Extremely low frequency fields", Environmental Health Criteria 238 — context for the ELF epidemiology band and its interpretation.
- Karipidis, K. et al. (2024), "The effect of exposure to radiofrequency fields on cancer risk in the general and working population", Environment International — the WHO-commissioned systematic review cited above.
Educational information, not medical advice. Every classification quoted here is as published by its dated source; this page paraphrases those sources and adds no health claims of its own. The IARC Monographs are the authoritative text — see About and Methodology for our editorial position.