To trace an allergic reaction you undergo a patch test.
Are you allergic to shrimp, fish or seafood?
Tem reação alérgica com camarão, peixe ou frutos do mar?
Did you have any kind of allergic reaction to medicines with iodine?
Alguma vez apresentou reação alérgica a medicamentos iodados por via oral ou cutânea?
In Brazil sometimes people refer to "something that appears in the skin" (skin manifestations) [symptoms] like shingles, rashes, other cutaneous or skin conditions, cutaneous disorders, etc...as "reação alérgica" ou algo similar - "reação parecida com reação alérgica". That, until it´s established what condition it is.
So, from experience not always that someone say he/she had "uma reação alérgica" it is "uma reação alérgica". Or, somebody can say that now and say what it is with the real name of the disease or condition afterwards.
That is, until proven otherwise "everything" (or almost) is "uma reação alérgica" in Brazil, more so if it involves (early) skin manifestations.