Almost as quickly as they became extensions of our own hands, cell phones, which emit low amounts of nonionizing radiation, started stirring up conversations over cancer risks. 

In 2011, the World Health Organization's International Agency for Research on Cancer listed radio-frequency radiation from cell phones as possibly carcinogenic based on limited information at the time. This wasn't a definitive claim, but rather a call for more research on whether radio-frequency electromagnetic fields, or RF-EMFs, from mobile phones could pose an actual threat to human health and increase cancer risk. 

In recent years and across different research pools, the general consensus has become that while it's difficult or impossible to certainly say that cell phone or technology use isn't linked to cancer — given the relative newness of such use, and the necessary caution around drawing conclusions in scientific research — there isn't credible or reliable evidence linking phones to health effects in humans, including cancer. 

This week, a large systematic review commissioned by WHO put an even finer point on it, finding from a final selection of 63 studies from 1994 to 2022 that radio-frequency radiation from mobile phones likely doesn't increase the risk of brain cancer. 

"If we're talking about these major health concerns, I think we have the answer pretty much," Dr. Timothy Rebbeck, professor of cancer prevention at the Harvard T.H. Chan School of Public Health and professor of medical oncology at the Dana-Farber Cancer Institute, said about the back-and-forth over cell phones and cancer risk. And according to Rebbeck, though there's less research on newer technologies such as Bluetooth devices than there is on cell phones, the fact that they're all emitting low amounts of the same type of generally harmless radiation should put tech users at ease.

Revisiting the phones-and-cancer conversation might feel like a moot point for some tech aficionados, but the limitations of smaller and earlier studies; the nature of how cancer occurs (it often takes many years for tumors to develop); and the way we've grown to become completely dependent on cell phones has made it difficult to firmly rule out long-term health risks from cell phones, or consumer tech in general. In addition to using cell phones, we're now literally wearing technology in the form of smart rings and smartwatches, sleeping with it, exercising with it and even relying on it to tell us when to get up and stretch our legs.   

As our dependence on consumer technology grows, so should our expectation of research that continues exploring whether it's harmless for us to use. From brain cancer to sperm count, here's what we know today about research on cell phones, radiation, Bluetooth and health.

What cell phones emit: Nonionizing radiation vs. ionizing radiation

Ionizing radiation is the type of radiation found in nuclear power. To different degrees, it's used in radiation therapy and medical diagnostic scans such as X-rays and CT (computed tomography) scans. 

We're exposed to low levels of radiation every day, even in nature, according to the US Centers for Disease Control and Prevention. However, exposure to ionizing radiation is cause for concern, as it's able to penetrate the body's cells effectively and — in large doses — has been found to pose health risks in humans because it can damage DNA.

The technologies with which we've developed up-close-and-personal relationships, including cell phones, emit low levels of
nonionizing radio-frequency radiation, which can't effectively alter cells the way ionizing radiation can. According to the US Food and Drug Administration, ionizing radiation carries more than a billion times more energy than nonionizing radiation.

Equipment that transmits radio-frequency radiation has to meet exposure limitations set by the US Federal Communications Commission, and wearable devices emit very low levels of nonionizing radiation. Besides mobile tech, radio-frequency radiation is found in other everyday items, including light bulbs, GPS gadgets and microwaves. 

Basically, we have nothing to worry about when it comes to cell phones and nonionizing radiation, "biologically speaking," according to Rebbeck. 

"It's radiation, but it's not the kind of radiation that really causes cancer," he said. "The only setting in which nonionizing radiation is really known to cause cancer is sun exposure."

Rebbeck said that some of the cancer concerns around cell phones comes from findings that technology may generate heat, which can affect tissue and cells similar to what occurs with a sunburn or a cooking mishap. 

But the way people use devices in general should mitigate this risk, making this mostly irrelevant to human exposures, he added. For instance, you aren't going to continue to hold a too-hot device up to your skin. And also, heat like that probably means something's wrong with your phone. 

Health fears around Bluetooth devices reach wellness circles: Do Bluetooth devices cause health risks?

Some people have expressed concerns over the impact of devices that rely on Bluetooth, a technology that uses radio frequency to transmit signals over short distances. 

But for people concerned about RF-EMFs, relying more heavily on Bluetooth devices rather than a phone may actually be the preferred method. According to the National Cancer Institute, research has found that Bluetooth devices like earbuds and headphones emit short-range signals that give off radio-frequency waves at powers 10 to 400 times lower than cell phones. 

"We don't have the same kind of data that we do from cell phones, but there's not any evidence that type of [Bluetooth] exposure should be able to cause cancer in normal use," Rebbeck said, adding that the radiation dissipates very fast.

"If you have a Bluetooth device and you hold it a foot away from you, there's no radiation that you're being exposed to really," he said. 

Sperm count, fertility and different cell phone questions 

Suggestions from medical experts that men who are trying to conceive should avoid exposure to hot laptops (or other warm objects) have to do with the fact that healthy sperm production is affected by high temperatures near the testes. Still, the impact of cell phone use on sperm quality and count has been an increasing subject of debate over the years.

One years-long study, published in December 2023 in the journal Fertility and Sterility, found a correlation between increased mobile phone use and poorer semen quality, though the study's authors wrote that the association was strongest between 2005 and 2007 and decreased as the years went on, suggesting that the "transition to new technologies" and "corresponding decrease in the phone's output power" may have leveled any potential impact.

In another WHO-backed systematic review published this summer, on the potential impact of radio-frequency exposure on male fertility, researchers found that there may be little or no effect on sperm or semen quality from carrying your phone in your front pocket, and no conclusive evidence of fertility impact from RF-EMF and mobile phone use. They also called for more rigorous studies. 

Reproductive health has been a largely understudied area of medicine in general, and scientists are just beginning to understand that hormones and factors that influence reproductive health may be affected by many elements of our environment. These elements include pollution, additives to our food, scents in everyday products and more. 

Cancer risk bottom line 

Cell phone use aside, there are lifestyle and health factors that firm evidence links to cancer risk. According to Rebbeck, we should be most concerned about smoking cigarettes, eating a lot of highly processed food and drinking alcohol. 

"There are plenty of things you can choose in your life that change your risk dramatically," Rebbeck said.