This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
The earliest and most marked evidence of the constitutional action of iodine, whether taken by the mouth or injected hypodermically, is furnished by irritation and catarrh of the mucous membranes. If iodine itself be used, as in the form of tincture, there is more liability to local irritation of the mouth and stomach than with the alkaline iodides, but the distal mucous irritation is the same with all forms of the drug. It is shown mostly in the throat and bronchi, the nose and eyes - parts that are all exposed to contact with carbonic acid gas, which it is supposed decomposes the iodide salt as it is eliminated, so that free iodine exerts its local irritant effect (Rabuteau). Others trace a similar decomposition to contact with ozone in the blood or in the air (Buchheim and Kammerer: Virchow's Archiv). The irritation shows itself by pain and sense of pressure over the frontal sinuses, oedema, prickling, and heat about the nose and eyes, with sense of stuffiness and serous discharge like that of ordinary coryza. The dose that will produce these symptoms varies much with different persons, some being acutely affected by 1 or 2 gr., others not by 10 or even 20 gr. continued daily for a long time.