Last week we got one of those periodic reminders that nobody knows whether cellphones may be seriously affecting our health. That worries me, given the ubiquity of these phones in our world today, and the fact that most of you reading this hold one to your head.

The latest study to hit the news is one from Sweden that finds long-term cellphone users seem to have a significantly increased risk of developing a type of serious but non-cancerous brain tumor. The study found that the risk of developing such a tumor was about doubled for long-term phone users, and that phone users with such tumors were four times more likely to have the illness on the side of their head where they typically held the phones. Last year, another study, also from Sweden, found a link between cellphone radiation and brain damage in rats.

None of this necessarily means you shouldn’t use a cellphone, or even that to do so is dangerous. But they remind us again that health effects, even possibly serious ones, cannot be ruled out. The CTIA, formerly known as the Cellular Telecommunications Industry Association, and now rebranded "The Wireless Association," issued a typically ambiguous statement: "This is just one study on this particular subject and no conclusions can be drawn from it." They added, "more research is needed in this area to provide definitive answers to any questions that might still exist. Numerous independent scientific bodies have conducted research on possible health effects from using wireless phones and it is widely accepted that no conclusive link can be made." All technically true, but not very helpful.

There have been numerous studies over the past decade and a half that suggest there could be a health risk from using today’s cellphones. However, there have also been many studies that found no risk. The problem is that studying the impact of any kind of electromagnetic radiation on human health is a maddeningly complex science.

It will never be possible, as the CTIA implies, to determine conclusively if cellphones are either safe or unsafe. The nature of epidemiology—studies of the incidence of disease in human populations—is such that it can never show causation.

The most obvious method of reducing any potential risk is not to hold the phone’s radio transmitter, which emits a strong microwave signal, close to your brain. That’s your body’s most sensitive tissue. A headset is a bit inconvenient. But to use one is a classic example of what’s called "prudent avoidance." Even using a clamshell phone that puts the phone’s antenna at a slight angle away from the head may be helpful. The intensity of microwave radiation decreases exponentially with distance, so even two inches can make a gigantic difference in how much radiation reaches your brain.

I began writing extensively about the health effects of electromagnetic fields in the late 1980s, and wrote a big story in our March 8, 1993 issue entitled, "Do Cellular Phones Cause Cancer?." The subhed included this phrase: "One researcher for Motorola wouldn’t use them more than 30 minutes a day." I got my own first cellphone not long after that (from Motorola, in fact), and have mostly used a headset ever since. But it can be very inconvenient wrestling with those ridiculous cords, and I eagerly await phones like the next generation Treo from Palm, soon to be released. I’m told it will include Bluetooth wireless so my earpiece can be connected to the phone with a very weak local wireless signal.

That article back in 1993 caused quite a ruckus. Motorola was not thrilled, to say the least. The researcher in question was Ross Adey, a neurologist who spent over 30 years examining the health effects of electromagnetic fields. I published an interview with Adey in October 2000. I pulled it down this week and a few quotes jumped out at me:

"The epidemiology suggests…health effects that are cumulative over time from exposure to non-ionizing electromagnetic radiation—whether it be 60 hertz power-line fields, today’s type of radio and microwave communication, or ultrawide-band technology."

Note that he’s not saying "injury," but "health effects." Adey said we don’t know how serious those effects might be. But Adey strongly believed that children should never be allowed to hold a cellphone to their heads, and continued to limit his own use to no more than half an hour a day. He was concerned not only about the use of phones but the growth of what he called "electronic smog." "Increasingly," he said, "wherever we go, we will be immersed in a sea of low-level, pulsed microwave signals."

Adey was not entirely grim, however, suggesting that eventually wireless communications could move towards infrared, which does not, by definition, penetrate human tissue. But Adey felt we needed to work much harder than we have done so far to determine what might be an acceptable level of microwave signals in our environment. We won’t hear more from this pioneer. He died in May at age 82.

It’s true as the CTIA says that more research is needed, but it’s also true that this enormously profitable industry has never been willing to spend more than a few million dollars trying to better understand the health implications of a business from which it earns many billions in profits. That’s a shame.

Questions? Comments? E-mail them to me at dkirkpatrick@fortunemail.com.