There are disinfectants and cleaners that contain iodine. These would be considered toxic to consume. Only the correct types of iodine are safe to consume in the proper amounts.
Back in the day, doctors prescribed iodine routinely but a bogus study or two came out and caused a lot of people to think iodine was dangerous. After the Wolff-Chaikoff effect sent waves of fear across the planet, only a few were brave enough to get involved again.
Iodine can cause halide, heavy metal and parasite detox, some people can interpret this as an allergy or toxicity to iodine. If a person is very toxic, only a few drops of iodine can cause a decent detox reaction. Most of the time, toxins are taking the place of nutrients. So by focusing on nutrition, we may be able to replace the toxins.
Diabetics and people taking Synthroid may need to be more cautious while starting iodine. These can be indicators of iodine deficiency, and iodine will cause a lot of new processes to start happening, which can be startling or uncomfortable, especially when very low on iodine.