iodine

This purple-black element is not just something people once kept in first aid kits for cuts and scrapes. It is also an important nutrient that helps the thyroid gland work properly. The thyroid helps control growth, energy use, and development, so even a very small amount matters.

You can get it from foods like seafood, dairy products, and iodized salt. In medicine, it has long been used to help kill germs on the skin. If the body does not get enough of it, a person can feel tired or unwell because the thyroid cannot do its job as it should. It was first found in seaweed, which is still known as a rich natural source.

Iodine is a chemical element with the symbol I and atomic number 53. At room temperature, it is a dark purple-black solid, and when heated, it can turn into a violet vapor. That striking color helped give it its name, which comes from a Greek word meaning "violet."

It was first isolated from seaweed in 1811 by the French chemist Bernard Courtois. For many people, the word brings to mind old-fashioned first aid: brown antiseptic liquid painted onto cuts and scrapes to help kill germs. That medical use is real, but it is only part of the story.

Its most important job is inside the body. It is an essential nutrient needed to make thyroid hormones, which help control metabolism, growth, and development. Because of this, people need small but regular amounts of it in their diet. Seafood, dairy products, seaweed, and iodized salt are common sources. When the body does not get enough, the thyroid cannot work normally, and this can lead to health problems such as tiredness, weight gain, or trouble with growth and brain development, especially in children.

It also has uses outside health and nutrition. It has been used in photography, in laboratory work, and in some chemical and industrial processes. So while it may seem like a small detail in a bottle of antiseptic or a pinch of table salt, this purple-black element plays an important part in both science and everyday life.