Part of the show Pain relief - the contributions of genes, spider venom and chillies
How is it that visible light and radio waves are harmless, but microwaves and gamma rays have adverse effects on life? There seems to be no linear path from the least harmful to the most harmful in the spectrum. The harmless waves seem to be interspersed with the harmful ones as you climb up the spectrum. Is there an explanation for this?
There are two different mechanisms going on here. The first is that as you get higher frequency waves, such as gamma rays and UV waves and X-rays, what you actually get are more energetic waves. They can cause ionisation, which is incredibly bad, and DNA damage and in that case problems for life. The energy of those waves is powerful enough to rip molecules apart. Microwaves are something slightly different. Microwaves are bad because water specifically absorbs microwaves and converts the microwave energy into heat. That's how your microwaves work at home. The microwaves are absorbed by the water in the food, which creates heat, so if you're irradiated by high-intensity microwaves, you're actually cooking yourself. However, microwaves are non-ionising so it doesn't damage your DNA and it can't trigger cancer like ultraviolet radiation could or gamma rays or x-rays.