Cell phones are potentially carcinogenic according to the International Agency for Research on Cancer (IARC), a branch of The World Health Organization. A panel of 31 scientists from across the globe did not conduct any new research before making the declaration, but assessed existing studies.

The IARC has now elevated cell phone use to its Group 2B list of carcinogens, which includes many different chemicals and products, such as DDT, engine exhaust, and coffee, pickled vegetables and talcum powder. This means it the IARC considers cell phones “possibly carcinogenic to humans.” The panel evaluated a number of research studies, including the 2007 Interphone study, which indicated that the heaviest 10 percent of cell phone users had a 40 percent increased risk of developing a rare type of brain tumor called glioma. Because this cancer is so rare, the increase in risk is very slight.

Importantly, it remains unclear how the kind of non-ionizing radiation emitted by cell phones may lead to cancer.

As the Cancer Research UK blog points out:

So far no one has been able to provide a good biological mechanism for the link between mobile phones and cancer. The “how” question is an open one. The phones give off microwave radiation, but this has millions of times less energy than, say, an X-ray and is not powerful enough to damage our DNA. They mildly heat the body, but again, not enough to pose a health risk. Other suggestions have been put forward, but none are backed by consistent evidence.

According to some, the new IARC classification is no cause for alarm. Matthew Herper writes at Forbes.com:

If there is a reason to care about this data, it’s this: if there is any risk of glioma, you could probably avoid it by using an earpiece or speaker phone for long cellphone conversations, and we could encourage cellphone manufacturers like Apple, Motorola, and Nokia to design their phones to help people do that. Glioma is a terrible cancer, and if we could reduce the number of cases through simple means it would be worth it.

But cellphones also improve our lives in numerous ways, and the evidence of risk just doesn’t warrant much change. We could probably improve our health a lot more by avoiding charred meats, wearing sunscreen, eating vegetables, and helping people quit smoking. The cellphone cancer story just isn’t that scary—it’s barely even a pickle.

The Daily Telegraph’s health correspondent Martin Beckford adds:

So how good is the evidence? To be blunt: not very. There have been a number of studies done into the link between mobile phones and cancer. Most of them show no increase in risk.

But many experts—including the director of the IARC—recommend taking sensible precautions like texting or using hands sets rather than holding the phone to your ear for too long. Others think there more dramatic action is in order, as the Washington Post reports:

[…] some experts said the conclusion should lead to immediate action, not only by consumers but also by the Food and Drug Administration and the Federal Communications Commission.

“This is the first formal acknowledgment that we may have a problem on our hands — and it could be a very big problem,” said Louis Slesin, editor of Microwave News, a trade publication. “The IARC decision, surely, is a wake-up call that people, especially children, should take sensible precautions.”

CNN Health points out problems with the Interphone study, suggesting that it may in fact have underreported the risk of developing cancer:

In general, the Interphone study has many flaws. Among them, participants self-reported how much they used their phones, and memory isn’t always accurate. Also, Interphone does not include children and young adults, who could be at increased risk of brain disease from cell phone radiation. Interphone also fails to address cordless phone use. But the bottom line is that while it doesn’t prove with absolute certainty that anything causes anything, it is still a reason to pause and think about your cell phone use.

While reactions to the new classification have run the gamut, David Ropeik, author of a book on the perception of fear, says public response is a typical one to fearful news on a guest blog at Scientific American:

We’re more afraid of human-made risks (radiation from cell phones) than natural ones (radiation from the sun), and we’re more afraid of things that cause high pain and suffering—like brain cancer—than risks which cause less painful outcomes.