Radiation is caused by tiny particles that cannot be seen or smelled. Small amounts can be tolerated by the body, but large amounts cause illness and death by affecting rapidly reproducing cells like those in the gut and bone marrow. Radiation sickness occurs in stages depending on the amount of radiation exposure, and can result in bone marrow destruction, severe dehydration, or circulatory collapse leading to death. Some tips for protecting oneself include minimizing time in contaminated areas, maximizing distance from explosions, shielding the body, and washing potential radioactive particles from victims.