The thyroid gland is responsible for making hormones that control the body's metabolism. The thyroid uses iodine to make its hormones. It is not able to distinguish between non-radioactive and radioactive iodine. When a person is exposed to radioactive iodine, it collects in the thyroid and damages the cells of the gland. This damage can lead to thyroid dysfunction and thyroid cancer. As seen in the aftermath of the Chernobyl explosion, exposure to radioactive iodine significantly increases thyroid cancer rates. Potassium iodide can be highly effective at limiting the absorption of radioactive iodine and reducing the risk of thyroid cancer.