Wearables have arrived. But some doctors and scientists say the latest must-have technology may pose serious health risks to the people wearing them.

Internet-connected glasses, smart watches and health monitoring gadgets put wireless technology right on the body, increasing exposure to radio waves among consumers who are already carrying wireless smartphones, tablets and laptops.

Make no mistake … Wearables like Google Glass, Samsung Gear Live and the upcoming Apple Watch are a growing tech category. Wearable smart device shipments will more than quadruple globally by 2017, reaching 116 million units, compared to an estimated 27 million this year, according to a September report from Juniper Research, a U.K-based market research firm that specializes in wireless technology.

The good news is that most wearables use Bluetooth technology, which emits much lower levels of radiofrequency, or RF, than cellular-based smartphones and other devices that use Wi-Fi.

For example, wearables from Fitbit use Bluetooth Low Energy, which is a “lower power technology than classic Bluetooth typically used in headsets, and operates at powers dramatically lower than cellphones,” a company spokeswoman told Foxnews.com in an email.

In fact, she added, the output power of Fitbit’s trackers is so low, the FCC does not require them to be tested for Specific Absorption Rate (SAR), a measure of the rate at which energy is absorbed by the human body when exposed to RF radiation, including microwave radiation). Cellphones and laptops, on the other hand, must pass strict SAR testing requirements, since they operate at higher power levels.

But many wearables don’t limit their radiation to Bluetooth. Products like Google Glass, Recon Instruments’ Recon Jet and Optinvent’s ORA use Wi-Fi, too. And that is sounding the alarm for some health professionals.

“Wi-Fi is very similar to cellphone radiation. You definitely don’t want to put these devices near your head or near your reproductive organs” for extended periods of time, said Joel M. Moskowitz, Ph.D., director of the Center for Family and Community Health at the UC Berkeley Prevention Research Center School of Public Health.

Because Google Glass operates on Wi-Fi, it has a relatively high SAR of 1.42, Moskowitz said. (The upper SAR limit that is considered safe is 1.60.)

Google did not respond to a request for comment.

But does a low SAR rating make a wearable safe? Moskowitz has his doubts.

“The SAR in itself is a problematic standard, because basically it was derived to protect against the acute effect of heating from microwave radiation,” he said. “It’s kind of a bizarre standard, because the effects the health community are concerned about are not thermal in nature. They’re the lower intensity exposures that are chronic over time. So the whole SAR framework is outdated.”

And outdated standards can be a problem for consumers looking for guidance from health professionals, because “Many in the medical community are oblivious to the potential health risk of microwave radiation,” Moskowitz said.

There are reasons that the medical community is not waving their arms about the risks of RF radiation exposure, however.  A study of about 360,000 cellphone users in Denmark, for example, concluded that there is no increased risk of brain tumors based on long-term use.

And the intensity of a Wi-Fi signal is generally less than that of a cell phone.  

Health Canada, a Federal department that advises Canadians on health issues, has published guidelines “based on scientific evidence” that “determined that low-level exposure to radiofrequency (RF) energy from Wi-Fi equipment is not dangerous to the public.”

But there is something called the precautionary principle that states when an activity is potentially harmful to human health, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically.

One who is being cautious is Hugh S. Taylor, MD, chairman of the Department of Obstetrics, Gynecology and Reproductive Sciences at the Yale School of Medicine.  Though wearables emit lower energy levels than smartphones, some people should still consider themselves at risk, he said.

“My warning is that we should be particularly cautious in pregnant women,” Taylor told Foxnews.com. “Especially something such as a watch if you have your arm straight down or resting on your belly.”

And sporting a wearable in addition to carrying a smartphone and tablet could have a cumulative effect, he said.

“I worry that wearables may increase our total exposure. All that radiation will be adding up. Wearables are something you’re more likely to keep on your body, so you’re more likely to have a sustained close exposure.”

Taylor, most of whose work focuses on fetal development, said fetuses exposed to radiation from their pregnant mothers’ cellphones can develop behaviors such as hyperactivity, poorer memory and ADHD (Attention Deficit Hyperactivity Disorder) in childhood.

But the effects of RF radiation on the average consumer are what concern Moskowitz.

“If [you] were to go to the NCI (National Cancer Institute) website, [you] would probably read that there’s been a lot of research. [They would say that] we really don’t know the answer, and more research is needed,” he said. “That’s the conventional party line of our government and many governments around the world.”

Echoing Taylor’s concerns, he added: "Besides the peak RF exposure from Bluetooth devices, which is what the SAR measures, we need to be concerned about the cumulative RF exposure, as people may keep these devices on all day long."

For example, he said, one of the effects of daylong, very low intensity exposure to microwave radiation from Wi-Fi is that it “opens the blood brain barrier. So if you have any toxins in your blood system, those toxins can now penetrate your brain tissue with very, very low exposure to microwave radiation.”

Even Bluetooth, where the SAR is low, “could be problematic leaving [the device] near the head, because of the blood brain barrier phenomenon,” Moskowitz said.

But the risk of RF radiation is insignificant when a wearable can help a person in dire need of medical care, said David O. Carpenter, MD, director of the Institute for Health and the Environment at the University at Albany (N.Y.).

“You have to evaluate what the risk is. It has to be balanced against the benefit. If you have a wearable that’s monitoring a disease state, that’s a very different issue,” Carpenter told Foxnews.com.

He brought up the case of a girl with a severe form of Type 1 diabetes.

“She has to have a finger prick with the blood glucose level measured every two hours. And there’s a new device that can be implanted that will monitor glucose and then feed back with wireless technology to a pump that would inject insulin. And there’s also a feature that, by wireless technology, will project information to a monitor that could be in the parents’ bedroom.”

In cases like this, Carpenter said, it’s very likely that the benefit “grossly exceeds the risk.”

Beyond the debate about RF radiation exposure, safety experts have expressed concerns about the likelihood of accidents, because wearables distract the attention of people who are driving, bicycling and even walking.

Earl Miller, a professor of neuroscience at MIT who specializes in multitasking, told NPR that people are fooling themselves if they think it’s safe to drive with Google Glass.

“You think you're monitoring the road at the same time, [but] that's an illusion. It can often lead to disastrous results,” he said.

And a report in Forbes cited an ophthalmologist, Sina Fateh, saying products like Google Glass can cause visual confusion.

“The problem is that you have two eyes and the brain hates seeing one image in front of one eye and nothing in front of the other,” Fateh said. Documented problems include binocular rivalry, visual interference and phoria, a misalignment of the eyes that is a result of both eyes no longer looking at the same object.

But RF radiation remains the biggest concern. For the first time, wireless devices are being worn on the human body, which means there is a potential for extended exposure. And cumulative exposure adds up if consumers are already using a cellphone, tablet and laptop.

“It’s the total dose and it’s the dose over time,” Carpenter said. “The more things you put directly on your body, the greater the exposure.”