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The WHO's cancer agency reviewed all available studies through 2011 and concluded that radiofrequency electromagnetic fields — including those emitted by mobile phones — are "possibly carcinogenic to humans." The decision was based primarily on an observed increased risk of glioma (a brain cancer) in heavy mobile phone users.

Group 2B means there is limited evidence in humans and limited evidence in animals — not proof of causation. Coffee, pickled vegetables, and engine exhaust are also Group 2B. The classification is widely cited but also widely debated. It has not been updated since 2011.

The NTP's final report concluded there was "clear evidence" that male rats exposed to high doses of 2G and 3G cell phone radiation developed malignant heart schwannomas (a tumor of nerve sheath tissue). There was also "some evidence" of brain gliomas and adrenal tumors.

Important context: the rats were exposed at whole-body levels (1.5–6 W/kg) far higher than typical phone use, for nine hours a day across two years. The U.S. FDA disagreed with the "clear evidence" framing, noting the exposure conditions don't directly translate to human use. Effects were not observed in female rats or in mice.

A meta-analysis combining ten previous studies found that mobile phone exposure was associated with an 8.1% reduction in sperm motility and a 9.1% reduction in viability. Effects on concentration were less consistent. Results held across both lab (in vitro) and population (in vivo) studies.

The authors called for further research before clinical conclusions. Mechanisms proposed in the literature include thermal effects from phones carried in pockets and oxidative stress from RF exposure to testicular tissue.

A Swedish case-control study followed patients diagnosed with the most aggressive form of brain cancer (glioblastoma multiforme). Patients who had used wireless phones for more than 20 years showed roughly twice the risk compared with non-users (hazard ratio 2.0 for mobile phones; 3.4 for cordless phones).

Hardell's research group is one of the most prolific in this area but has also been criticized by other epidemiologists for methodology, particularly recall bias in patients reporting their phone use. Other large cohort studies (Danish, Million Women Study) have not replicated the strong association.

The WHO's most recent systematic review of human observational studies on RF-EMF and cancer concluded there was "moderate-certainty evidence of no or only a small effect" for major cancers including glioma and lymphoma. Evidence for thyroid and oral cancers was rated low or very low — meaning more research is needed, not that effects exist.

This is the most comprehensive review to date and is the WHO's basis for current guidance. Critics (see the next entry) argue the review's framing understates the animal evidence and downplays effects found below ICNIRP's stated threshold.

A systematic review of experimental studies on male fertility concluded that animal data showed adverse effects of RF-EMF on most fertility endpoints (sperm count, pregnancy rate). However, the certainty rating for human observational data was very low, primarily due to inconsistent exposure measurement across studies.

The authors noted that despite the uncertainty, "the associations between RF-EMF exposure and decrease of pregnancy rate and sperm count are not negligible" — particularly given declining male fertility in Western populations from other causes.

ICNIRP's 2020 guidelines (which most national regulators adopt) cover 100 kHz to 300 GHz, including 5G. Their conclusion: "RF EMF exposure below the thermal threshold is unlikely to be associated with adverse health effects." The "thermal threshold" is the level at which RF causes measurable tissue heating.

Limits are set well below this threshold with safety factors. Critics argue the thermal-only model ignores non-thermal biological effects observed in some studies, and that the safety factors are arbitrary. ICNIRP's position remains the regulatory consensus.

A PRISMA-guided review focused on children and adolescents — generally considered a more sensitive group due to thinner skulls, longer expected lifetime exposure, and developing nervous systems. The review found methodological weaknesses in most included studies and concluded the body of evidence does not currently support a particular risk to young people from typical wireless device exposure.

The authors note this is a research limitation, not a clean bill of health: studies designed to detect long-latency effects in children simply don't yet exist at sufficient scale.