Iodine is a chemical element that plays a crucial role in keeping your body healthy, especially your thyroid gland, which controls how fast your body uses energy. Without enough iodine, you might feel tired, have trouble concentrating, or grow more slowly than you should.

Your body can't make iodine on its own, so you need to get it from food. That's why table salt is often iodized, meaning iodine has been added to it. Before iodized salt became common in the 1920s, many people suffered from thyroid problems because they didn't get enough iodine in their diet. Seafood, seaweed, dairy products, and eggs also contain iodine naturally.

As a pure element, iodine appears as dark, shiny crystals that turn into a purple vapor when heated. You might recognize it as the brownish-red liquid sometimes used as an antiseptic to clean cuts and scrapes. When you see surgeons in movies with orange-brown stains on their hands before an operation, that's often an iodine solution used to kill germs.

Scientists use iodine in laboratories too. If you ever did an experiment testing foods for starch, you probably used iodine solution, which turns dark blue or black when starch is present.