News reports from Japan indicate that officials there are preparing to distribute iodide pills to citizens in order to prevent certain types of radiation sickness should a nuclear meltdown occur.

If the reactors at the Fukushima Daiichi nuclear power plant, or any of the others that have been damaged after the 8.9-magnitude earthquake and tsunami, does indeed melt down, several types of radioactive materials could be expelled into the environment. Cesium-137 and strontium-90 present long-term environmental hazards and can be absorbed throughout the body, particularly bones. Plutonium-239 exposure often leads to lung cancer, and it has a half-life of 24,000 years, so it would be around for a long, long time. (A half-life is the amount of time it takes for half of the radioactive isotopes in a substance to decay.)

But one of the most dangerous materials that could come out of the reactor is iodine-131. Iodine has a relatively short half-life of about a week, but it can do a lot of damage in that time. It will most likely escape in gas form, which makes it easy to pick up, and the body rapidly funnels it to the thyroid, where it can accumulate and cause cancer in a relatively short amount of time.

The good news is that, unlike the other three radioactive materials, there is a simple pill that will protect your thyroid from radioactive iodine. If a person takes a potassium-iodide pill (or liquid solution) before exposure occurs, the iodine in that pill will flood the body and, importantly, the thyroid. Once this occurs, even though your body will absorb radioactive iodine, it won’t be able to collect in the thyroid – the inert iodine blocks the bad stuff. Instead, the powerful carcinogen will be excreted from your system.

Prophylactic potassium iodide was first used, and to great success, during the Chernobyl disaster in 1986.