When small particles from these sources settle, the particles are called fallout. Unless one is directly in the path of the heaviest fallout, it is unlikely that there will be enough radiation to produce radiation sickness. But fallout usually contains elements such as radioactive iodine or radioactive strontium that are taken into the body. These are likely to increase the incidence of cancer. For example, radioactive iodine lodges in the thyroid, where it can produce thyroid cancer.
Radioactive strontium replaces calcium in the bones and can produce leukemia .
One way to reduce the chance of these substances causing trouble is to take ordinary iodine or extra calcium from a safe source. The body takes the safe element and tends to eliminate the radioactive one.