Iodine is definitely NOT for headaches. Here is a typical heath warning for pure iodine:
Poison! Danger! Corrosive. Causes severe irritation or burns to every area of contact. May be fatal if swallowed or inhaled. Vapors cause severe irritation to skin, eyes and respiratory tract. Strong oxidizer. Contact with other material may cause fire. Affects the cardiovascular and central nervous systems. May cause allergic skin or respiratory reaction.
If it is well diluted, iodine can be used as an antiseptic. A solution in alcohol is called 'Tincture of Iodine' and used to be found in first-aid cabinets for cleaning wounds but is less often seen today. I believe hospitals use iodine solution to sterilise the skin prior to an operation.