There has been a lot of debate and speculation over the years in regards to cell phones and the risks their radiation can have. But now, the World Health Organization (WHO) has officially categorized mobile phone use as a possible carcinogenic hazard.

In the past, studies have suggested that electromagnetic radiation could cause adverse effects on humans, such as brain tumors and problems with male fertility. The largest international study on cell phones and cancer, which was released in 2010, showed that volunteers who used cell phones over a 10-year period or longer had doubled the rate of a type of tumor called glioma. Another study conducted by the National Institutes of Health showed that cell phone radiation boosts brain activity by 7 percent, but it is still unknown what this artificial boost does to the brain. Some effects may not be known for many years. 

"When you look at cancer development -- particularly brain cancer -- it takes a long time to develop," said Dr. Henry Lai, research professor in bioengineering at University of Washington. "I think it is a good idea to give the public some sort of warning that long-term exposure to radiation from your cell phone could possibly cause cancer."

While it is important to note that WHO has not established any adverse health effects on humans, it has labeled cell phone radiation as "possibly carcinogenic to humans."

WHO came to this conclusion after a team of 31 scientists from 14 countries reviewed studies on cell phone safety, and as a result, placed cell phone radiation in the same carcinogenic category as engine exhaust, lead and chloroform. Cell phone radiation is non-ionizing, meaning its not like an X-ray, but more similar to a low-powered microwave. 

"What microwave radiation does in most simplistic terms is similar to what happens to food in microwaves, essentially cooking the brain," said Dr. Keith Black, chairman of neurology at Cedars-Sinai Medical Center in Los Angeles. "So in addition to leading to a development of cancer and tumors, there could be a whole host of other effects like cognitive memory function, since the memory temporal lobes are where we hold our cell phones."

While wireless carriers instruct users to keep cell phones a certain distance from their heads, such as Apple's iPhone 4 safety manual that says to keep the device at least 15 millimeters from the body, CTIA - The Wireless Association noted that WHO's announcement does not mean that cell phones cause cancer. In addition, the association denounced WHO's results since it "did not conduct any new research, but rather reviewed published studies."

The European Environmental Agency and others around the world are pushing for further research on the subject for a more in-depth understanding of radiation effects.