The thyroid can store or hold only a certain amount of iodine. In a radiation emergency, radioactive iodine may be released in the air. This material may be breathed or swallowed or ingested with food and drinks. It may enter the thyroid gland and damage it. The damage would probably not show itself for years.
Children are most likely to have thyroid damage.
If you take Potassium Iodide, it will fill up your thyroid gland and block the uptake of dangerous radioactive iodine. This greatly reduces the chance that harmful radioactive iodine will enter the thyroid gland. The slightly yellow surface is caused by a clear coating to prevent any bitter taste. Please see our article on Nuclear Power Plant Hazard Issues for reasons why this is a major problem in the U.S. today. If a child cannot swallow this pill, the pill should be crushed and administered in milk, juice, jam, soda, etc. to eliminate the bitter taste taken once per day.