Salt
The amount of iodine and the specific iodine compound added to salt varies from country to country. In the United States, the Food and Drug Administration (FDA) recommends [21 CFR 101.9 (c)(8)(iv)] 150 micrograms of iodine per day for both men and women. US iodized salt contains 46–77 ppm (parts per million), whereas in the UK the iodine content of iodized salt is recommended to be 10–22 ppm.
Iodine in biology
pmid: 29437784 DOI: 10.1530/ERC-17-0515Elemental iodine is an oxidizing irritant, and direct contact with skin can cause lesions, so iodine crystals should be handled with care. Solutions with high elemental iodine concentration such as tincture of iodine are capable of causing tissue damage if use for cleaning and antisepsis is prolonged. Although elemental iodine is used in the formulation of Lugol's solution, a common medical disinfectant, it becomes triiodide upon reacting with the potassium iodide used in the solution and is therefore non-toxic. Only a small amount of elemental iodine will dissolve in water, and adding potassium iodide allows a much larger amount of elemental iodine to dissolve through the reaction of I2-I3. This allows Lugol's iodine to be produced in strengths varying from 2% to 15% iodine.