Do Cell Phones Cause Brain Cancer? What 25 Years of Studies Show

Cell phones have not been shown to cause brain cancer. Over roughly 25 years, the large studies that followed hundreds of thousands of people forward in time have found no rise in brain tumors among phone users, and brain tumor rates haven’t climbed the way they would if phones were a major cause. In 2024, a review commissioned by the World Health Organization rated the evidence as moderate certainty that holding a phone to your head does not increase the risk of glioma or other head tumors.

That’s not the same as “proven safe.” A few studies found higher risk among the heaviest users, and nobody can yet rule out a small risk after several decades of use. That remaining doubt is why the International Agency for Research on Cancer (IARC) still lists radiofrequency fields as “possibly carcinogenic.”

The studies disagree mostly because of how they were designed, so this guide sorts them by design.

Why This Question Is Hard to Answer

Glioma, the brain tumor researchers worry about most, is diagnosed in only a handful of people per 100,000 each year. Detecting a small increase takes either enormous numbers of people or careful comparison of patients with healthy controls, and each approach has its own weakness.

Among human studies, the worrying results come almost entirely from the first row.

The Case-Control Studies: Where the Concern Started

Interphone

Interphone, coordinated by IARC across 13 countries and published in 2010, was the largest case-control study of phones and brain tumors, with 2,708 glioma cases in its main analysis.

For most users, Interphone found no increase in risk. In nine of the ten groups sorted by lifetime call time, the glioma odds ratios came out below 1.0, which would mean phone users had less glioma than non-users. Since there’s no plausible way phones would protect against cancer, that pattern pointed to bias in who took part or how they remembered their use.

The exception was the top tenth: people who recalled 1,640 or more hours of cumulative call time. Their odds ratio for glioma was 1.40 (95% confidence interval 1.03–1.89), about 40% higher odds. But that group included implausible answers. When researchers removed the 60 participants who reported more than five hours of calls per day, the elevated results lost statistical significance. The study group concluded that biases and errors prevented a causal interpretation.

The Hardell studies

Lennart Hardell’s group in Örebro, Sweden, ran a series of case-control studies starting in the late 1990s. They consistently reported stronger associations than Interphone, particularly among long-term users and people who started using phones before age 20. Supporters argue that their exposure measures were better. Critics point to recall bias and to the fact that other independent groups haven’t reproduced the effect sizes. These studies carried real weight in the 2011 IARC decision; our broader cancer research review covers them in more detail.

MOBI-Kids

To fill the gap on children, MOBI-Kids recruited 899 young people aged 10 to 24 with brain tumors and 1,910 controls in 14 countries between 2010 and 2015. Published in 2021, it found no evidence of a causal link between brain tumors and use of mobile or cordless phones. The authors added that sources of bias in the study meant they couldn’t rule out a small increased risk.

The Cohort Studies: Following People Forward

Cohort studies avoid the memory problem by recording phone use before anyone is diagnosed.

The Danish subscriber cohort (2011)

Danish researchers linked 358,403 mobile subscribers to the national cancer registry: 3.8 million person-years from 1990 to 2007. Among people with subscriptions of 13 years or longer, the incidence rate ratio for central nervous system tumors was 1.03 in men, essentially no difference. There was no trend with years of subscription, and no excess of tumors in the parts of the brain closest to where a phone is held.

But a subscription is a crude stand-in for how much someone actually talks. The authors themselves said they could not rule out small to moderate increases among heavy users, or risks that appear only after 15 years or more.

The UK Million Women Study (2022 update)

This study followed 776,156 British women who answered questions about phone use in 2001, for an average of 14 years. During that time, 3,268 brain tumors were diagnosed. The relative risk for ever using a phone compared with never using one was 0.97 (95% CI 0.90–1.04) for all brain tumors. Daily use and ten or more years of use showed no significant increase either.

The women were born between 1935 and 1950, and few used phones as heavily as many people do today, so the study says more about typical use than heavy use.

COSMOS (2024)

COSMOS recruited 264,574 adults in Denmark, Finland, the Netherlands, Sweden, and the UK between 2007 and 2012, asked about their call time at enrollment, and then tracked them through cancer registries. In a median of about seven years of follow-up, the risk of glioma didn’t change with call time: the hazard ratio per 100 cumulative hours of calls was 1.00. For people with more than 15 years of use it was 0.97, and for the heaviest tenth of users it was 1.07, with a wide confidence interval (0.62–1.86).

That wide interval is the main limitation. Only 149 gliomas occurred during follow-up, so COSMOS can’t yet exclude a modest risk among heavy users.

The Population Test: Where Are the Extra Tumors?

If phones caused even a modest share of gliomas, brain cancer rates should have climbed some years after phones became nearly universal. The registries don’t show that.

• Australia. A 2018 study in BMJ Open examined 16,825 brain cancer cases in adults aged 20 to 59 from 1982 to 2013. There was no increase in any brain tumor type, including glioma and glioblastoma, during 2003–2013, the period of heavy phone use. Glioma of the temporal lobe, the part of the brain closest to a phone held at the ear, didn’t increase either. A 1990s rise in glioblastoma was attributed to MRI making these tumors easier to diagnose, and a follow-up in people over 60 found the same pattern.
• United States. Analyses of the National Cancer Institute’s SEER registry data show glioma incidence rising from 1975 to 1987, before phones were widespread, and declining slightly through 2018. Glioblastoma, one glioma subtype, rose modestly over the same period.

As the National Cancer Institute notes, population rates can’t detect a small increase limited to heavy users or to a susceptible subgroup. They do rule out a large effect on the general population.

What the Rat Studies Add

The US National Toxicology Program spent more than a decade and about $30 million exposing rats and mice to cell phone signals. Its final 2018 reports found “clear evidence” of malignant schwannomas in the hearts of male rats, and “some evidence” of malignant gliomas in the brains of male rats. Female rats and mice showed no comparable findings.

The exposures were extreme by human standards: whole-body, 9 hours a day, lifelong, at levels near or above the absorption limits set for phones. The NTP stated that its results shouldn’t be applied directly to human phone use. Still, a carefully run federal study that found tumors in the same cell types flagged in some human studies (glial cells and Schwann cells, the cells acoustic neuromas form from) is a big reason the question hasn’t been closed.

Where the Official Assessments Stand

• IARC (2011): classified radiofrequency fields as Group 2B, possibly carcinogenic to humans, based on limited evidence of glioma risk among heavy users. Group 2B means the evidence is suggestive but not convincing. It says nothing about how large any risk would be.
• WHO-commissioned systematic review (2024): screened more than 5,000 papers published between 1994 and 2022 and included 63 in the final analysis. It found moderate-certainty evidence that phone use doesn’t increase the risk of glioma, meningioma, acoustic neuroma, pituitary tumors, or salivary gland tumors in adults, or brain tumors in children. Some critics argue that the reviewers’ ties to ICNIRP, the body that sets international exposure guidelines, colored the conclusions.
• IARC’s next step: in March 2024, an IARC advisory group listed radiofrequency radiation as a high priority for re-evaluation in 2025–2029, while suggesting that the review take place in the second half of that window, so late 2027 at the earliest. Listing doesn’t guarantee a review.
• US agencies: the National Cancer Institute and the FDA both maintain that current evidence does not show phones cause cancer in people.

Summary of the major human studies

If You Want to Cut Your Exposure Anyway

The evidence doesn’t call for alarm, but the open questions about decades of heavy use make cheap precautions reasonable:

• Distance does most of the work. RF absorption falls steeply as the phone moves away from your head. Speakerphone, a wired headset, or texting instead of calling cuts head exposure far more than choosing a different phone. Our SAR explainer covers why distance matters more than the rating. Wireless earbuds also put out far less power than a phone; see our AirPods guide.
• Avoid long calls on a weak signal. Phones raise their transmit power when the signal is poor, so a call with one bar exposes your head to more than the same call with full bars. This is also why your phone usually matters more than the tower down the street.
• Don’t shop by SAR alone. SAR ratings reflect a lab test at maximum power. Lists like this Visual Capitalist ranking of 15 popular phones are interesting, but gaps between compliant phones are small next to distance and signal.
• For kids, set habits early. Children weren’t well represented in the early research, and MOBI-Kids couldn’t exclude a small risk. Texting, speakerphone, and keeping phones off pillows overnight are easy to teach.

To see how your phone compares with the other sources in your routine, the EMF exposure quiz ranks them in a few minutes.

Frequently Asked Questions

Can holding your phone to your ear cause a brain tumor? Large cohort studies, including COSMOS with more than 260,000 adults, found no increase in glioma, meningioma, or acoustic neuroma with more call time. A few case-control studies found higher risk among the heaviest users, but those results may reflect recall bias. A small risk after decades of heavy use hasn’t been completely ruled out, so using speakerphone or a headset is a reasonable, free precaution.

Why is cell phone radiation classified as possibly carcinogenic? In 2011, IARC classified radiofrequency fields as Group 2B based on limited evidence of glioma among heavy phone users, mainly from the Interphone and Hardell studies. Group 2B describes how strong the evidence is, not how large a risk would be. IARC has listed RF for possible re-evaluation, no earlier than late 2027.

Are children more at risk from cell phone radiation? Some modeling studies suggest children’s smaller heads absorb RF somewhat differently, and today’s kids will accumulate more lifetime use than any earlier generation. MOBI-Kids, the largest study of young people, found no causal link between phone use and brain tumors but couldn’t exclude a small risk. Precautionary habits cost nothing.

Do 5G phones increase brain cancer risk? Most of the cancer research involves older network generations, but 5G phones operate within the same exposure limits, and phones on most 5G bands work at frequencies similar to 4G. Engineering studies of 5G phones, such as the one in our 5G brain exposure study spotlight, estimate low absorption in brain tissue. The habits that reduce exposure from any phone, distance and good signal, apply equally to 5G.