If, for some reason, you find yourself in a situation where you need to wash radioactive material from your body, don't reach for the bottle of hair conditioner. Conditioner can bind radioactive particles to your hair. That warning was part of guidelines issued last Friday by Guam's Office of Civil Defense, following threats from North Korea that it was preparing to test a missile that would create an "enveloping fire" around the U.S. territory. On Tuesday, North Korean state media reported it would not carry out the test after all.

Still, the guidelines, which also include information on how to take cover before an explosion, are correct. They're the same guidelines posted on the U.S. Department of Homeland Security's website, Ready.gov. The reason conditioner can be dangerous has to do with the physical characteristics of human hair, the chemistry of hair conditioner and properties of nuclear fallout.

When a nuclear warhead detonates, a fireball incinerates everything it touches and hurls the vaporized material skyward. Buildings, rock and living things are turned to dust and get mixed up with the radioactive byproducts of uranium or plutonium atoms splitting. This dust, called nuclear fallout, leaks a steady stream of dangerous radiation. If you're unlucky enough to be caught outside during or after an explosion, fallout can settle onto your clothing and skin. Some of these particles are so small they can slip into crevices that lie open on strands of human hair. If you look at a strand of hair in a high-powered microscope, you'll see proteins that look like overlapping scales.