In case of a nuclear accident, radioactive iodine may be released. This can enter the body through the airways or via contaminated food. The thyroid gland absorbs this iodine, which leads to an irradiation 'from the inside'. The chance of cancer or other disorders then increases.
By taking stable, non-radioactive iodine at the right time, you ensure that your thyroid gland is already saturated and no longer absorbs radioactive iodine. However, iodine tablets do not provide protection against other radioactive substances. That is why it is necessary for you to be able to take shelter quickly.