June 2, 2011 -- After a World Health Organization study concluded cell phones may cause cancer, some are wondering what else in their homes and their everyday lives may be just as, or even more, dangerous to their health.
The World Health Organization, whose International Agency for Research on Cancer announced the results of its year-long cell phone study Tuesday, estimates that there are 5 billion cell phone users globally, representing nearly three-quarters of the world's population.
A family of those 5 billion cell phone users can be found in the New York City home of Steve and Elizabeth Howard,and their two young sons, 9 month-old, Luke, and three year-old, Graham.
Steve and Elizabeth, owners of five cellphones and an iPad among them, were initially calm in reacting to the multi-country study released by WHO that found people who used cell phones most often, an average of 30 minutes per day over 10 years, had a 40 percent higher risk for a rare brain tumor called a glioma.
"I kind of let it go in one ear and out the other," Steve, the father, told "Good Morning America."
The Howards' ambivalent response could be a case of "the boy who cried wolf," a response to the roughly 30 other studies that have tried, and failed, to establish any link between cell phones and cancer since cell phones hit the consumer market in the late 1970s.
What's More Dangerous, Cell Phones or Microwave Ovens?
One study even found those who used cell phones occasionally had a lower cancer risk than those who used old-fashioned land lines.
But the latest decision from WHO placed cell phones on a list of possible carcinogens that includes the pesticide DDT and gasoline engine exhaust.
Working as a hairdresser is considered riskier than using a cellphone, according to the IARC's classification system, achieving "probable carcinogen" status. Other possible carcinogens include working as a dry cleaner or a firefighter.
Findings such as those in the WHO study have prompted cell phone users like the Howards to question what else could be lurking in their homes as a possible cancer risk. And are the radiation levels really that dangerous?
ABC News brought in Michael Knox, an electrical engineering professor at the Polytechnic Institute of New York University to examine the Howards' home, testing their cell phone, Wi-Fi enabled computer and microwave, each a vital part of the Howards' daily life.
While there were measurable levels of radiation emanating from all the devices, Knox, who is not a medical doctor, said he was not particularly concerned by the levels.
The consensus among many doctors and experts to the WHO study is the data on cellphone use and brain cancer is still inconclusive.
"While experimental evidence and very limited human studies suggest that we should be cautious, people should realize there are many things we are exposed to every day that also is classified by IARC as possibly carcinogenic," said Dr. Peter Shields, chief of Georgetown University Hospital's cancer genetics and epidemiology program in Washington, D.C. "The classification used by IARC for cellphones is the lowest of all the carcinogenic classes, and no one should think that cell phones pose the same risk as smoking and asbestos."
The WHO decided, in effect, to err on the side of caution.
Microwave Ovens May Be More Dangerous Than Cell Phones
"[The] IARC is saying that we should be cautious and think through what we do when we regulate exposures from cell phones," Shields told ABC News. "They follow the precautionary principle and want to maximally protect public health."
Nevertheless, some experts believe the evidence, inconclusive as it is, warrants caution. ABC News reached out to 92 physicians, 65 of whom said they would continue to hold their cellphones up to their ear, but 27 said they will use hands-free devices to minimize their risk.
The Howards say they too will now take similar caution when it comes to their electronics.
"My children are so young I would want to limit the amount that they're interacting with this sort of stuff," said Elizabeth, noting she had previously allowed even 3-year-old Graham, to have his own cell phone, although it was not set up to make calls.
Researchers at the University of Utah established that the radiation dose is much higher inside the brains of 5- and 10-year-olds than in adults, a major concern as more children adopt cell phones.
Cell phone safety options for the Howards, and the world's other 5 billion cell phone users, include texting more and talking less, or using hands-free devices.
"Use a wired ear piece, that absolutely has a minimal amount of radiation, or even use a Bluetooth which has substantially less radiation than a cell phone," advised Dr. Leonard Lichtenfeld, Deputy Chief Medical Officer for the American Cancer Society, to ABC News.
In the U.S., the Federal Communication Commission set a maximum limit of 1.6 watts per kilo of body tissue. However, they did not test phones being carried directly in a person's pocket, just inside of belt holsters. So far, the recommendation continues to be to hold your cell phone about one inch away from your body.
ABC News' Katie Moisse and Michael Murray contributed to this report.