here is the difference

getting good benefit from Iodine means it is strengthening normal healthy function. but if Iodine is causing a problem, it is not the Iodine causing it any more than oxygen is causing oxidative stress. the cure is not stopping taking in oxygen. the cure is to find out what the exposure is to toxins and what nutrients are missing.

the more severe the reaction the more iodine is indicated as deficient.

my guess? you could use some selenium and boron.