IARC Group 2B Explained: What "Possibly Carcinogenic" Means

“Possibly carcinogenic to humans” is the label the International Agency for Research on Cancer (IARC) gave radiofrequency electromagnetic fields in May 2011, placing them in Group 2B. The label means a panel of scientists found some evidence that RF exposure might cause cancer, mainly glioma in heavy cell phone users, but not enough to call the link probable or established. It’s a statement about how strong the evidence is, not about how dangerous a phone is. Group 2B says nothing about dose, and it doesn’t estimate how many cancers, if any, RF would cause.

The label usually gets quoted as either an alarm bell or a punchline, and neither use reads it correctly. Below: how IARC’s system works, what else sits in Group 2B, how the 2011 decision was made, and what could change next.

How IARC’s Classification System Works

IARC is the World Health Organization’s cancer research agency, based in Lyon, France. Its Monographs program convenes international working groups that review published research on a single agent (a chemical, a habit, an occupation, a type of radiation) and sort it into one of four groups.

The counts come from IARC’s own running list, which covered Monographs volumes 1 through 142 at its October 2026 update.

There used to be a fifth group: Group 4, “probably not carcinogenic.” Only one agent ever landed there (caprolactam, a nylon ingredient), and IARC dropped the category in its 2019 rule revision. That’s worth knowing because it shows how the system is built. IARC asks whether something can cause cancer under some circumstances. It is not designed to clear things, and Group 3 does not mean “safe”. It means the evidence is too thin or too conflicting to decide.

Hazard versus risk

The most important distinction in reading any IARC label is the one the agency itself makes:

• Hazard is the capacity to cause cancer at some level of exposure, under some conditions.
• Risk is the likelihood of cancer at the exposures people actually experience.

IARC rates hazard only. Plutonium and sunlight are both in Group 1 because the evidence that each can cause cancer is strong. The groups don’t tell you which one you should worry about more on a given Tuesday.

The aspartame review in July 2023 shows the difference most clearly. On the same day, IARC put aspartame in Group 2B based on limited evidence for liver cancer, and a separate WHO/FAO committee, JECFA, which assesses risk, kept the acceptable daily intake at 40 mg per kg of body weight. For a 70 kg adult, that works out to roughly 9 to 14 cans of diet soda a day before reaching the limit. Both conclusions stood, because they answered different questions.

No equivalent risk assessment comes attached to the RF classification. Exposure limits from the FCC and ICNIRP are built around preventing tissue heating, and whether they adequately cover non-thermal effects is its own long-running fight; our explainer on the FCC limits lays out both sides.

What gets something into Group 2B

Under the current rules, an agent lands in 2B through one of three routes:

1. Limited evidence in humans: a credible association that chance, bias, or confounding can’t be ruled out as the explanation.
2. Sufficient evidence in experimental animals, with inadequate human data.
3. Strong mechanistic evidence, showing that the agent behaves like known carcinogens at the cellular level, even without good human or animal data.

RF came in through the first route. The animal evidence in 2011 was rated limited, which is a big part of why the classification didn’t go higher.

What Else Is in Group 2B

People often point out that RF shares a category with pickled vegetables, as if that settles the matter. The 2B list is a grab bag of 329 agents with nothing in common except evidence of roughly similar strength:

Some comparisons that circulate online are now out of date:

• Coffee was in 2B until 2016, when a new review moved it to Group 3. (Very hot beverages of any kind went to 2A, because of the heat.)
• DDT went up to 2A in 2015.
• Talc went up to 2A in 2024.
• Gasoline itself was classified as Group 1 in 2025; only engine exhaust remains in 2B.

The pickled-vegetable comparison misleads in both directions. It makes RF sound trivial, but that classification rests on real associations in populations that eat a lot of them. Membership in a group tells you the evidence is suggestive; anything more requires reading the evidence.

ELF magnetic fields, the low-frequency fields from power lines and household wiring, are the other EMF entry on the list, classified nine years before RF. That classification rests on a different body of evidence, covered in our article on power lines and childhood leukemia.

The 2011 Vote

IARC’s working group on RF met in Lyon from May 24 to 31, 2011: 31 scientists from 14 countries, chaired by US epidemiologist Jonathan Samet. They evaluated three exposure categories: occupational exposure to radar and microwaves, environmental exposure from broadcast and telecom transmitters, and personal use of wireless phones.

Their conclusions, summarized in The Lancet Oncology that summer and in full in Monograph Volume 102 (2013):

• Human evidence: limited, for glioma and acoustic neuroma among wireless phone users. This rested mainly on the Interphone study and the Swedish case-control studies led by Lennart Hardell. IARC’s press release cited one finding in particular: a 40% higher glioma risk in the heaviest category of past phone users in Interphone.
• Human evidence: inadequate for every other cancer type.
• Animal evidence: limited.

The Lancet Oncology summary said the 2B evaluation “was supported by a large majority of Working Group members.” It was not unanimous. Some members thought the human evidence was weaker than “limited,” because Interphone’s elevated results came only from its top usage group, which included implausible self-reported call times, and because most of its other groups showed odds ratios below one. Our brain cancer evidence review walks through why those patterns suggest recall and selection bias.

The classification applies to RF fields as an agent, not to phones specifically. A cell tower, a WiFi router, and a radio transmitter are all covered by the same 2B label, even though the evidence behind it came almost entirely from phones held against the head. The towers and routers in your environment typically deliver far lower exposure than that.

What Has Happened Since 2011

The evidence base has grown considerably since 2011, and it points in more than one direction:

• Large cohort studies found no rise in brain tumors. The UK Million Women Study (2022) and the five-country COSMOS study (2024) both followed hundreds of thousands of people forward in time and saw no increase in glioma with phone use. Brain tumor rates in countries like Australia and the US haven’t climbed the way they would if phones were a major cause.
• A WHO-commissioned systematic review (2024) rated the evidence as moderate certainty that phone use does not raise the risk of glioma and other head tumors. Critics argue its authors had too many ties to ICNIRP; the long-running dispute over that review process is covered in our article on the WHO EMF review controversy.
• Animal evidence got stronger. In 2018, the US National Toxicology Program reported “clear evidence” of heart schwannomas and “some evidence” of brain gliomas in male rats exposed to lifelong, whole-body RF. The Italian Ramazzini Institute reported schwannomas in rats at lower exposures. Both found tumors in the same cell types flagged in the human studies.

This is why the classification could plausibly move either way. Under IARC’s rules, stronger animal evidence plus limited human evidence is one standard route to Group 2A. Meanwhile, the human evidence for glioma has arguably weakened since 2011, and a working group could reasonably rate it as inadequate.

The Pending Re-evaluation

In March 2024, an IARC advisory group recommended radiofrequency radiation as a high priority for re-evaluation during 2025–2029, while suggesting that the review take place in the second half of that window so that newer studies could be included.

As of November 2026, IARC’s announced meetings run through October 2027 (Meeting 144, on lead and cadmium), and none of them covers RF. IARC typically announces a meeting and calls for experts about a year in advance. That makes late 2027 the earliest realistic date for an RF review, and 2028 or 2029 more likely. Being on the priority list does not guarantee a meeting will happen.

Possible outcomes:

The makeup of the working group and the evidence available at the time will decide which.

How to Read “Possibly Carcinogenic” in Practice

When you see the 2B label in a headline, product ad, or city council debate, a few points help:

• It’s a call for more research, not a finding of harm. Group 2B means a credible signal that hasn’t been confirmed.
• It says nothing about dose. The classification doesn’t distinguish a phone pressed to your ear for hours from a router across the house. Exposure falls steeply with distance, which is why our SAR explainer puts more weight on how you hold a phone than on which phone you buy.
• Watch out for misused comparisons. “Same as pickled vegetables” is a rhetorical move. Ask what the evidence for RF shows.

For most people, the sensible response is proportionate precaution with the device closest to the body: speakerphone or wired earphones for long calls, avoiding long calls on a weak signal, and keeping phones off the pillow. Our broader cancer research review covers the other cancer endpoints studied. To see which sources in your own routine carry the most exposure, the EMF exposure quiz ranks them in a few minutes.

Frequently Asked Questions

Is cell phone radiation classified as a carcinogen? IARC classifies radiofrequency electromagnetic fields, including the signals phones use, as Group 2B, “possibly carcinogenic to humans.” That is the third of four tiers and means limited evidence of a cancer link. RF is not classified as a known (Group 1) or probable (Group 2A) carcinogen.

What is the difference between Group 2A and 2B? Group 2A (“probably carcinogenic”) generally requires stronger evidence, such as limited human evidence combined with sufficient evidence in animals or strong mechanistic data. Group 2B usually reflects limited evidence from one stream alone. Neither group measures how large a risk is.

Is WiFi classified as possibly carcinogenic too? Yes. The 2011 classification covers radiofrequency fields as a category, so WiFi, Bluetooth, and cell towers fall under the same label as phones. The evidence behind it came almost entirely from people holding phones to their heads, though, and exposure from a router across the room is far lower.

Are power lines Group 2B? Extremely low-frequency (ELF) magnetic fields, the kind produced by power lines and household wiring, have been in Group 2B since 2002, based on an association with childhood leukemia. That decision was separate from the 2011 RF decision and rests on different evidence.

When will IARC re-evaluate cell phone radiation? In 2024, an IARC advisory group made RF a high priority for 2025–2029 and suggested the second half of that period. As of November 2026, no meeting has been announced, and IARC usually announces meetings about a year ahead, so a new decision is unlikely before late 2027.