10 Iodine Facts

Facts about the Element Iodine

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Iodine is an element you encounter in iodized salt and the foods you eat. A small amount of iodine is essential for nutrition, while too much is toxic. Here are facts about iodine.

The name

Iodine comes from the Greek word iodes, which means violet. Iodine gas is violet-colored.


Many isotopes of iodine are known. All of them are radioactive except for I-127.


Solid iodine is blue-black in color and shiny. At ordinary temperatures and pressures, iodine sublimates into its gas, so the liquid form is not seen.


Iodine is a halogen, which is a type of non-metal. Iodine possesses some characteristics of metals, too.


The thyroid gland uses iodine to make the hormones thyroxine and triiodotyronine. Insufficient iodine leads to development of a goiter, which is a swelling of the thyroid gland. Iodine deficiency is believed to be the leading preventable cause of mental retardation. Excessive iodine symptoms are similar to those of iodine insufficiency. Iodine toxicity is more severe if a person has a selenium deficiency.


Iodine occurs in compounds and as the diatomic molecule I2.

Medical Purpose

Iodine is used extensively in medicine. However, some people develop a chemical sensitivity to iodine. Sensitive individuals may develop a rash when swabbed with tincture of iodine. In rare cases, anaphylactic shock has resulted from medical exposure to iodine.

Food Source

Natural food sources of iodine are seafood, kelp and plants grown in iodine-rich soil. Potassium iodide often is added to table salt to produce iodized salt.

Atomic Number

The atomic number of iodine is 53, meaning all atoms of iodine possess 53 protons.

Commercial Purpose

Commercially, iodine is mined in Chile and extracted from iodine-rich brines, notably from the oilfields in the US and Japan.