In recent years, public fears over the radiation emitted from cell phones have led to several theories about the health conditions this radiation might engender.
Almost invariably, the assertions that the use of cell phones may lead to a higher risk of brain cancer, that their use by pregnant women may result in badly behaved children -- even a video that suggested that the waves from two cell phones could be used to cook an egg -- have been discredited by scientific investigation.
"Current scientific evidence doesn't indicate any adverse health outcomes associated with exposure to radio frequency energy from cell phones," U.S. Food and Drug Administration spokeswoman Peper Long told ABCNews.com last May.
"Although there have been reports of negative health effects from low levels of radio frequency energy, these reports have not been replicated or confirmed."
So those who suspect their phones are frying their brains can likely rest easy. However, research and anecdotes have suggested a number of other means by which cell phones may adversely affect health -- and possibly not in the way you might think.
New research released Thursday suggests that one cell phone-related health threat that many people face may not be from their own phones at all -- but from their doctors' mobile devices.
In a study published in the journal Annals of Clinical Microbiology, researchers at Ondokuz Mayis University in Samsun, Turkey screened the mobile phones of 200 health care workers in hospitals for germs that are known to be dangerous to human health.
What the researchers found was that 94.5 percent of the phones tested -- nearly 19 out of 20 -- were contaminated with some kind of bacteria. Worse, some of the bacteria that the researchers found were known "superbugs" -- bacteria that are resistant to one or more commonly used antibiotics.
Despite this, the researchers found that only about 10 percent of the health care workers studied cleaned their cell phones on a routine basis.
"Mobile phones are frequently-used devices with clean or dirty hands in daily practice, including in hospitals," Dr. Ahmet Dilek of the Ondokuz Mayis University team told ABCNews.com. "[W]e found that most of the medical professionals do not clean their own cell phones, and most of the [unclean] phones carried important hospital pathogens."
Dr. Charles Gerba, a microbiologist and germ expert at the University of Arizona in Tucson, has performed similar studies on cell phones. He said that his past research, too, has found that cell phones are a haven for a variety of microbes -- some of which are pretty nasty.
"We have found [the superbug] MRSA on several cell phones," he said. "So we certainly find a lot of stuff on them -- particularly the flip kind, since they have surfaces that do not dry out."
The solution to this problem may be decidedly low tech -- disinfectant spray and a paper towel.
"I think that they should wipe [their cell phones] down with a disinfectant wipe, or spray a towel with disinfectant and wipe the phones off," Gerba said. "They should be doing that at least once a day, if not maybe twice a day."
While the radiation that emanates from cell phones may not be enough to affect our brains, the conversations themselves might.
Specifically, researchers at Carnegie Mellon University studied the brain waves of drivers using cell phones -- and they found that even just listening to a conversation reduced the amount of brain activity devoted to driving by 37 percent. The quality of driving showed a "significant deterioration," according to the 2008 study.
"The science tells [us] when [we're] on the phone while driving, it is a high-risk activity -- very, very risky," Janet Froetscher, president and CEO of the National Safety Council, told ABC News correspondent Lisa Stark in a "World News" report in January. "But most people don't understand that."
Still, 80 percent of drivers admit to having had a cell phone conversation while driving, according to a May 2008 Nationwide Insurance poll -- even though more than 40 percent of those surveyed said they'd been hit or almost hit by another driver who was talking on a cell phone.
Even hands-free phones appear to contribute to unsafe driving. A 2005 study by the Insurance Institute for Highway Safety found that drivers using cell phones -- even hands-free -- were four times as likely to have an accident involving an injury, according to Ann McCartt, senior vice president for research at the insurance institute.
"I think there is still a big misconception among drivers and policymakers, intuitively, that a hands-free phone would be safer," she said. "And there may be a margin of safety there, but it is still unsafe."
Those behind the wheel may not be the only ones at risk of a cell phone-related auto accident. So suggests a study published in January in the journal Pediatrics that shows that children are more distracted while crossing the street if they happen to be talking on a cell phone.
Using a virtual reality setting, researchers studied 77 children ages 10 and 11 to see what effect cell phone conversations had on their ability to make it across the street safety.
What they found was that when children were on the cell phones, their attention to traffic -- the number of times a participant looked right or left -- went down 20 percent. The risk of getting hit by a car, or the number of close calls, went up 43 percent.
"The influence of cell phones on child pedestrian safety is particularly concerning because cell phones, an oddity a decade ago, are quickly becoming ubiquitous among American schoolchildren," said the study's authors.
Some preliminary studies show that even adult pedestrians get distracted while carrying on cell phone conversations while walking. Still, adults are much more likely to avoid injury, as they are generally more adept at navigating the crosswalk than children are.
While they may pale in comparison to the seriousness of a car accident, the "phantom" vibrations experienced by some habitual mobile device users can be an annoying side effect of the wireless era.
Indeed, many cell phone and BlackBerry users report feeling vibrations when their phones are, in fact, silent.
"If you use your cell phone a lot, it becomes part of you," Dr. William Barr, the chief of neuropsychology at the New York University School of Medicine, told ABCNews.com. "It's like wearing a tight sock all day. When you take it off, you still feel it there on your foot. If your cell phone is not there, you still feel like it is."
Our reliance on our cell phones may actually be "training" some of us to believe it is vibrating when it is not. In the case of cell phones, people are rewarded when they pick up their calls and read their incoming text messages, which causes them to pick up their cell phones more and more frequently.
"People are rewarded when they are able to detect low amplitude vibrations so they get better and better at responding," said Jon Kaas, a professor of psychiatry at Vanderbilt University. "It is very rewarding to get the message, so people are able to train their system to detect that signal."
As people repeat this behavior over and over again, connections between nerves in their brain become stronger and new ones are formed, which helps to make the behavior automatic.
And sometimes, as is the case with vibrating cell phones, the behavior becomes too automatic.
"People have gotten so good at detecting vibrations that they start responding to false positives -- they think something is there when it is not," Kaas said.
When it comes to the possible downsides of mobile device use, the side effects are not all in our heads. Our thumbs, it turns out, may also bear the brunt of our reliance on these devices.
The sores and blisters that some experience from too much texting and typing have earned monikers such as "BlackBerry thumb." And while the sore thumbs may seem like a new phenomenon, medical experts say there is a rational explanation for this modern-day nuisance.
"They are really repetitive stress injuries -- pain, numbness, discomfort in the base of the thumbs from overuse," Margot Miller, a physical therapist and president of the Occupational Health Section of the Orthopedic Section of the American Physical Therapy Association, told ABCNews.com.
These sorts of injuries, known as repetitive strain injuries or a repetitive motion disorders, are sometimes minor. But they can also lead to serious medical problems.
"I've seen a significant increase in the number of people with pain in their tendon regions in their thumbs and their fingers," Dr. Richard Brown, an orthopedic hand surgeon at the Scripps Memorial Hospital in La Jolla, Calif., said.
"I have to send them to the therapist or start them on medicine or put them in splints or, sometimes even operate."
Those with allergies to certain metals, such as nickel, may experience yet another side effect of exposure to their cell phones in the form of contact dermatitis.
In recent years, dermatologists have begun to see an increasing number of contact dermatitis patients who are allergic to these metal components in their cell phones.
"Some people are extremely nickel-sensitive," Dr. Lionel Bercovitch, a professor of dermatology at Brown Medical School, told Kirk Fernandes of ABC News OnCall.
Nickel is a metal that's used in a wide variety of products, including jewelry, belt buckles and watch bands. It's the most common cause of contact dermatitis in the developed world.
The symptoms of a nickel reaction range from mere redness to an obvious rash, or even blisters.
"My guess is that [the reactions are] probably more common than we think, but it's just not widely recognized," he said.
In a study published in the Canadian Medical Association Journal in January 2008, Bercovitch tested 22 models of cell phones for the presence of nickel. He found that 10 devices contained the metal -- often around the menu buttons, near decorative logos, around the edge of the screen or on a part of the handset where paint was chipped.
"As more cases get reported, more people will begin to think about it," Bercovitch said.
Ok, so mobile phones are not the only devices that must share blame for exposing our ears to potentially loud noises. But as the convergence of technology brings more and more of our gadgets together, a growing number of people are using their mobile phones to store and play their favorite music.
The only problem? They may be playing this music far too loudly for their own good.
According to statistics from the U.S. Centers for Disease Control and Prevention (http://www.cdc.gov/healthyyouth/noise/index.htm), about 12.5 percent of children and adolescents 6 and 19 years old and 17 percent of adults between 20 and 69 years of age have suffered permanent damage to their hearing from excessive exposure to noise. In total, this accounts for more than 30 million people.
Sounds louder than 85 decibels can damage hearing. Normal conversation is about 60 decibels, and stereo headphones out of our MP3-enabled devices often reach 100 decibels.
Fortunately, this noise-related side effect is easily remedied. Simply turning down the volume can limit chronic exposure to loud noises -- quite possibly ensuring that our future conversations on our cell phones continue to come in loud and clear.
Reports from Lisa Stark, Kirk Fernandes, Kamal Menghrajani and Carla Williams contributed to this report.
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