Concerning tincture of iodine: please help. I don't know what I've done.

Tincture of Iodine is made with ethanol. Ethanol is an alcohol and on the underside of your tongue would definitely make a burning feeling and could dry out the skin. I’m not a doctor so I am not 100% sure of the medical impact, but since you put it in your mouth then spit it out and rinsed, I’d say the chances of any negative impacts is pretty low.

Iodine is needed by your body. Your thyroid gland needs it. If you take too much your body will just purge it. Tincture of Iodine is made of some elemental iodine along with potassium iodine and possibly sodium iodine (salts) as well as the ethanol and water. I wouldn’t drink it, but the little bit you may have ingested will likely not hurt you.

In the future, look at the label. It probably says “topical” of “for external use only”. Use them that way. Any medications or first aid treatments you are planning to use should always be used per the instructions.

If you’re concerned, you can call poison control.

White streaks indicative of necrosis began to form, two hours after I submitted that question. Moreover, the frenulum of my tongue begins to feel really dry and as if it is constricting, when I drink water.

Go see the doc. We can’t help you.