All known cancer-inducing agents—including radiation, certain chemicals, and a few viruses—act by breaking chemical bonds, producing mutant strands of DNA. Electromagnetic radiation is absorbed by molecules as discrete packets of energy called “photons.” The energy of a photon is determined by the wavelength; the shorter the wavelength, the higher the energy. Not until the ultraviolet region of the electromagnetic spectrum is reached, beyond visible light, beyond infrared and far, far beyond microwaves, do photons have sufficient energy to break chemical bonds. It’s a little like trying to hit an object across a river with a stone. Even if your aim is poor, you might expect to hit the target now and then if you throw enough stones. But it won’t matter how many stones you throw if you can’t throw that far. Microwave photons heat tissue, but they do not come close to the energy needed to break chemical bonds, no matter how intense the radiation.

All known cancer-inducing agents—including radiation, certain chemicals, and a few viruses—act by breaking chemical bonds, producing mutant strands of DNA. Electromagnetic radiation is absorbed by molecules as discrete packets of energy called “photons.” The energy of a photon is determined by the wavelength; the shorter the wavelength, the higher the energy. Not until the ultraviolet region of the electromagnetic spectrum is reached, beyond visible light, beyond infrared and far, far beyond microwaves, do photons have sufficient energy to break chemical bonds. It’s a little like trying to hit an object across a river with a stone. Even if your aim is poor, you might expect to hit the target now and then if you throw enough stones. But it won’t matter how many stones you throw if you can’t throw that far. Microwave photons heat tissue, but they do not come close to the energy needed to break chemical bonds, no matter how intense the radiation.

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Cellular Telephones and Cancer: How Should Science Respond? – Park 93 (3): 166 – JNCI Journal of the National Cancer Institute

The reason your beautiful iPhone 4 doesn’t get a good signal when you’re holding it that way is because the FCC wants the antenna as far from your soft, soft brain as possible even though there is absolutely no mechanism by which cellphone radio waves could cause cancer. Next time in physics class, pay attention.