The effect of mobile phone radiation on human health is the subject of recent interest and study, as a result of the enormous increase in mobile phone usage throughout the world. Mobile phones use electromagnetic radiation in the microwave range, which some believe may be harmful to human health.
“Because people are always carrying their cell phones even in situations where they would normally wash their hands before doing anything, cell phones do tend to get pretty gross,” says Emily Martin, assistant professor of epidemiology at the University of Michigan School of Public Health. Research has varied on just how many germs are crawling on the average cell phone, but a recent study found more than 17,000 bacterial gene copies on the phones of high school students. Scientists at the University of Arizona have found that cell phones carry 10 times more bacteria than most toilet seats.
Certain countries have warned against the use of mobile phones by minors in particular, due to health risk uncertainties. In May 2016, preliminary findings of a long-term study by the U.S. government suggested that radio-frequency (RF) radiation, the type emitted by cell phones, can cause cancer.
On 31 May 2011, the World Health Organization stated that mobile phone use may possibly represent a long-term health risk, classifying mobile phone radiation as "possibly carcinogenic (having the potential to cause cancer) to humans" after a team of scientists reviewed studies on mobile phone safety. The mobile phone is in category 2B, which ranks it alongside coffee and other possibly carcinogenic substances.
Some recent studies have found an association between mobile phone use and certain kinds of brain and salivary gland tumors. Lennart Hardell and other authors of a 2009 meta-analysis of 11 studies from peer-reviewed journals concluded that cell phone usage for at least ten years "approximately doubles the risk of being diagnosed with a brain tumor on the same ('ipsilateral') side of the head as that preferred for cell phone use".