"I used to get a energy rush and zero scalp inflammation when taking only one drop of Iodine."
"The itchy scalp doesn't present itself on the surface. It looks completely normal, it's more of an internal thing."
This seems to be two different things; the latter more candida related (or parasites) the first more adrenal / inflammation/ low zinc and Iodine related.
Borax / Iodine have helped tremendously in scalp problems, even if it dosnt show on the surface. Itching in particular. I use it in my shampoo; I was a big time candida sufferer with the most itchy scalp.
Lugols Iodine with a touch of vit C is also a wonderful skin remedy in general; please try just to know what a great stuff you have available. Without the vit C it can be used to "burn" off a mole. etc etc
When it comes to excema that comes and goes; beware that Aspartame and other artificial sweeteners can cause this. (Doesnt have to be your case, but I answer for others as well)
My 11 year old son get an excema in his armpit if he drink as little as one glass of diet soda. Last time only a few weeks back. "I would not be impolite and say no , mummy" (so many kids birthdays etc with serving of only diet pop) After a week of two of itching he asked for help; and some iodine diluted in water + zinc salve on top took care of it within a day or two.