When my skin first got itchy with rashes that would come and go, it made no sense to me. I began keeping a food diary and it still made no sense to me.
One reason is that itchy rashes from foods - the IgG allergic reactions can occur hours to days after eating.
The second reason was that I was not even thinking about a cough medicine I was using ... it turned out I was allergic to the saccharin in it! I even ended up in the ER from one dose of saccharin in another liquid medication, after the hives turned worse, and every joint in my body swelled. I'd never heard of such a thing as allergic arthritis!
Then, I became allergic to aspartame, and then multiple foods... But underneath that all, it turned out I had probably been getting increasingly sensitive to other major foods as well - such as gluten and dairy.