Iodine is the chemical element with atomic number 53 and is essential for making thyroid hormones.
Its symbol is I, and it is a halogen. In the body, iodine is incorporated into the thyroid hormones thyroxine, also called T4, and triiodothyronine, or T3. These hormones help regulate metabolism, growth, and development.
Iodine deficiency can enlarge the thyroid gland, producing a condition called goiter. To reduce deficiency, many countries add small amounts of iodide or iodate to table salt. Iodized salt is a dietary source, while seafood and dairy products can also contain iodine.
Elemental iodine is a dark, lustrous solid that can produce a violet vapor when heated. It is not the same as iodide, which is a negatively charged iodine ion, or iodine tincture, an antiseptic preparation containing iodine compounds.