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.

A tale of two brains. On the left, a 3D viewer shows two brains; the stripes on outer surface represent expression of a gene in different areas of the cortex, while the dots (most of which are hidden under the surface in this view), reflect expression of the gene in deeper areas of the brain. Users can a dive deeper into the massive amount of quantitative and other data, as shown on the right.

Scientists have mapped the biochemistry and anatomy of two human brains in comprehensive detail, compiling the data into a publicly accessible database called the Allen Human Brain Atlas. In addition to maps highlighting where in the brain each gene in the genome is expressed, the atlas includes brain imaging data derived from magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI).

According to a release from the institute, the data "reveal a striking 94 percent similarity between human brains". In addition, "data analysis from the two human brains indicate that at least 82 percent of all human genes are expressed in the brain, highlighting its tremendous complexity while also providing an essential genetic blueprint to understand brain functionality better and propel research in neurologic disease and other brain disorders."

Pinky and the brain. A researcher examines a cross-section of the human brain stained to determine the quality and integrity of the specimen.

The human map follows release of a mouse version that the institute released in 2006. The human data will likely be used in studies examining a broad range of neurological disorders and cognitive functions, such as Parkinson's disease, schizophrenia, multiple sclerosis and even obesity. According to the institute, about 4,000 unique visitors are accessing the new Atlas each month.

A happy brain. The dots on this brain image indicate where the antidepressant Prozac acts on the internal structures of the brain. Researchers can drill down deeper for each dot and retrieve a detailed picture of the biochemistry at that location (analogous to a detailed view of everything in a particular neighborhood in a GPS).

"Until now, a definitive map of the human brain, at this level of detail, simply hasn't existed," said Allan Jones, Ph.D., Chief Executive Officer of the Allen Institute for Brain Science. "The Allen Human Brain Atlas provides never-before-seen views into our most complex and most important organ. Understanding how our genes are used in our brains will help scientists and the medical community better understand and discover new treatments for the full spectrum of brain diseases and disorders, from mental illness and drug addiction, to Alzheimer's and Parkinson's diseases, multiple sclerosis, autism and more."

Similar to a high-powered, multi-functional GPS navigation system, the Allen Human Brain Atlas identifies 1,000 anatomical sites in the human brain, backed by more than 100 million data points that indicate the particular gene expression and underlying biochemistry of each site. Scientists can use the Allen Human Brain Atlas to explore the human brain and identify how disease and trauma, including physical brain injuries and mental health disorders, affect specific areas of the brain. This powerful resource makes it possible to pinpoint where a particular drug acts anatomically in the brain, to ultimately better control the successful outcome of numerous therapies.

It is anticipated that the Allen Human Brain Atlas will be used in small and large-scale applications to examine diseases and disorders, such as obesity, Parkinson's disease, autism, schizophrenia, Alzheimer's disease and multiple sclerosis — as well as those exploring how the healthy brain works.

Illuminating Alzheimer's: Physicians can detect signs of Alzheimer's in the living human brain thanks to a new imaging tool. High levels of amyloid plaques, a hallmark of the disease, are marked in red. Credit: Avid Radiopharmaceuticals.

An advisory panel for the U.S. Food and Drug Administration gave conditional approval on Thursday for a new imaging agent that could aid in early detection of Alzheimer's. If the FDA follows the panel's recommendation, as it usually does, it will be the first such tool available to physicians to detect amyloid plaques, the neurological hallmark of the disease, in the living human brain.

As I noted in a story we posted yesterday on the technology, experts say the tracer will be especially useful in future research studies testing drugs designed to prevent the brain damage that causes Alzheimer's, as well as in diagnosing difficult and atypical cases of the disease.

The tracer, developed by Avid Radiopharmaceuticals (recently acquired by Eli Lilly) binds to amyloid plaques in the brain and is detected via position emission tomography (PET) scans. Previously, the only definitive way to detect amyloid in the brain, and hence definitely diagnose the disease, was via an autopsy.

The approval is conditional on the development of standards that make reading the scans consistent between radiologists and a doctor-training program. According to a report from the New York Times,

The question about interpreting the scans arose because in the Avid study, radiologists did not establish a firm cutoff point that would say whether a person had significant amounts of plaque. Instead they did a graded analysis. What is needed in practice is a set level that would say yes or no, and distinguish significant plaque accumulation from insignificant amounts. And the company must show that its cutoff points are accurate and that different radiologists assess the same scan in the same way.

Some people have plaque without having Alzheimer's, so if a scan shows plaque, doctors will have to use their clinical judgment, taking into account a patient's symptoms, in deciding what the scan results mean, noted Dr. P. Murali Doraiswamy, an Alzheimer's researcher at Duke University and a clinical investigator in the Avid trial. But if a scan shows no plaque, the situation is simpler, Dr. Doraiswamy said. It means the doctor should focus on other causes for the symptoms.