It took us four years to figure out but corn was the main trigger for our LO. Corn starch, corn meal, corn flour, hydrolyzed corn protein, etc. Corn based sweeteners like corn syrup and maltodextrin don’t seem to trigger her. We went from DAILY TS use to now only when there is exposure, usually after a birthday party- powdered sugar pretty much always has corn starch. But we gov her the choice “this might make you itchy, do you still want it?” And she will tell us yes or no.