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ROBERT SIEGEL, Host:

The World Health Organization has added cell phones to its very long list of things that could possibly cause cancer. The conclusion is far from definitive, but scientists reviewed studies and found that there is enough evidence to raise suspicions. This is the latest in a long back and forth over the health effects of using cell phones.

NPR's Richard Harris joins us now to talk about this development. Hi, Richard.

RICHARD HARRIS: Hi, Robert.

SIEGEL: And first of all, what does it mean when the World Health Organization says that something possibly causes cancer?

HARRIS: Well, this assessment comes from a branch of the WHO called the International Agency for Research on Cancer. And over the years, they've reviewed studies and ranked nearly a thousand chemicals and activities on a scale that goes from known cancer-causing agents to probably not carcinogenic.

In the history of this work, by the way, only one chemical has ever been declared not carcinogenic at all. So, but most things they've looked at fall into the category of possibly carcinogenic or not classifiable.

So those that fall into the possible category, which we're talking about here, have raised suspicions either in animal studies or in population studies. That would include, of course, many chemicals but also things like pickled vegetables, coffee, doing work as a carpenter. And now, the electromagnetic fields from cell phones.

SIEGEL: We'll skip carpentry and coffee. What's the evidence that the cell phone use might cause cancer?

HARRIS: Well, actually, quite a number of studies have looked at this and many find no link at all. But there are two big studies from Europe that do hint at something.

And what they do is they find a small group of people who use cell phones the very most were at a slightly increased risk for a cancer called glioma and also for another, benign head tumor.

Now, this is not definitive, but Dr. Jonathan Samet from the University of Southern California, who chaired the panel, said in a statement that, quote, there could be some risk and therefore, we need to keep a close watch for a link between cell phones and cancer risk.

SIEGEL: So if there is actually a link, how in theory might cell phones cause cancer, if they do?

HARRIS: Well, the phones use radio frequency waves to connect to nearby cell towers. So when you're on a call and holding the phone up to your ear, those waves are being received and transmitted right next to your brain.

However, this is not the kind of radiation that can actually break DNA molecules and cause mutations. It's not like an X-ray in that sense. So there's no really clear explanation for how these waves could actually be causing cancer, if indeed they are.

And unfortunately, animal studies on this don't really help clarify the picture.

SIEGEL: So it's a pretty confused picture. I mean, how would scientists go about sorting this out?

HARRIS: It is confused, and there are several large studies that are going on to help try to sort it out, one in Europe that actually could take several decades. So we may have to wait a while to get some answers.

And of course, the technology changes. So what you're studying now is the technology of a decade or so ago. So that doesn't always help.

The WHO finding also could encourage more animal studies and also, they're hoping, more careful cancer monitoring. For example, the WHO points out that there are no studies in children as yet.

SIEGEL: Well, since the WHO has said that it is possible that there might be some link between cell phone use and cancer, what - do they recommend that people do anything, or is this not even worth basing a recommendation on?

HARRIS: Well, the WHO is shy about making recommendations. They prefer to leave that up to individual governments. And the U.S. government, though, has reviewed not quite but pretty much the same studies that the WHO group did. And at least two agencies here, including the Food and Drug Administration, are not persuaded with the evidence at hand that cell phones do pose a cancer risk.

However, it's important to remember that new information is coming out all the time. So the issue does get re-evaluated periodically. Now, some of the individual scientists doing this work say if you are concerned about cancer, you can always use a hands-free device instead of holding up a cell phone up to your ear.

The other thing is that if there is a risk, I think it's fair to say it would be quite small because by now there's something like five billion people around the world who use cell phones...

SIEGEL: Use cell phones, yes.

HARRIS: Yeah, and this cancer, glioma, that's associated with it does not appear to be on the rise. So if there's a risk, it's a small one, or maybe there's a long time lag or something, but it's not cause for alarm in that sense.

However, I should say that it is clear that cell phones are a true public health in one sense, and that is the government says that more than 5,000 people are killed every year by distracted drivers in the U.S. alone. And, of course, cell phone use is one of the most common distractions.

SIEGEL: So our many listeners who are driving home right now might take that information onboard once again. Thank you, Richard.

HARRIS: My pleasure.

SIEGEL: NPR's Richard Harris, talking with us about the World Health Organization's finding that cell phones could possibly cause cancer.

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