Science Questions with Surprising Answers
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Dr. Christopher S. Baird

How long can you use a cell phone before getting a brain tumor?

Category: Physics      Published: December 19, 2012

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cell phone
Cell phones emit radio waves, which do not cause cancer. Public Domain Image, source: Christopher S. Baird.

Cell phones do not cause cancer, no matter how long they are used, because they communicate using radio waves. Radio waves simply don't have enough energy per photon to ionize atoms. The World Health Organization states, "Only the high frequency portion of the electromagnetic spectrum, which includes X rays and gamma rays, is ionizing". Cancer occurs when the DNA in a cell is altered so that the cell grows in an uncontrolled way. DNA can be altered in many ways, but when it comes to cancer due to radiation exposure, an electron must be knocked off a molecule by a bit of radiation. The smallest possible bit of electromagnetic radiation is known as a photon. Electrons are bound to molecules, so it takes a certain minimum energy to knock off the electron. Light with frequencies above ultraviolet (x-rays and gamma rays) are known as ionizing radiation because each photon has enough energy to knock an electron off a molecule. Photons of light with frequencies at and below ultraviolet (radio waves, microwaves, infrared, red, orange, yellow, blue, violet) are non-ionizing. They simply don't have enough energy to remove an electron and cause cancer.

Increasing the strength of a radio wave will not help it knock off electrons. Increasing the strength of a radio wave simply introduces more photons into the beam. But each radio photon still has the same energy it always does, which is not enough to ionize. When non-ionizing waves flow past a molecule, they shake up the electrons a bit but don't knock them off. This electron shaking leads to heating. A microwave oven heats up your food in the same way a campfire heats up your skin and in the same way a radio wave ever-so-slightly heats up your body. None of them causes cancer, no matter how long you sit there. You may get burned by sticking your hand in the fire or grabbing a hot dish right out of the microwave, but you won't get a tumor.

candle flame
A candle flame emits a thousand to a million times more energy per photon than a cell phone. Public Domain Image, source: Christopher S. Baird.

If a radio wave did cause cancer, then candlelight would cause far more cancer, because visible light has far more energy per photon. In terms of radiation, a candle emits far more energy than a cell phone, and they are both harmless. Infrared waves have more energy per photon than radio waves, and everything with a non-zero temperature emits infrared waves. This means that the infrared waves coming from your chair, your pencil, and your clothes would give you cancer long before radio waves from your cell phone would, but they don't. The world is swamped with natural radio waves and infrared waves. Just ask any infrared camera designer what his main obstacle is in designing a camera and he will tell you his greatest challenge is separating the meaningful waves from all the background waves in the air. Anybody who has struggled with an old-fashioned analog TV antenna in an attempt to get a clear picture can tell you that the natural radio waves in the air can be quite overwhelming compared to the man-made ones.

People who are worried about being bombarded with radio waves in our increasingly wireless world must realize that the sun and the rocks have been bombarding mankind with infrared and radio waves long before radio broadcast stations and WIFI routers came along. There are electromagnetic waves with high enough frequency to damage molecules: x-rays and gamma rays. That's why if you get too many x-ray scans taken you will get cancer. In addition, alpha, beta and neutron radiation can cause cancer, but they are only created by nuclear reactions, and not by cell phones. Any machine that produces x-rays is known to be dangerous and is heavily regulated in order to ensure safe use.

the electromagnetic spectrum
The electromagnetic spectrum. Only waves smaller than ultraviolet can damage atoms through ionization. All other waves interact with matter through simple heating. Public Domain Image, source: Christopher S. Baird.

Topics: brain, brain tumor, cancer, cell phone, phone, photon, photon energy, radiation, radio, radio waves