When stopping allergy meds like allegra, (fexofenadine) can a withdraw effect such as itching from head to toe occur?

Yes: When stopping an antihistamine relflex itching can occur.

Allegra (fexofenadine): If the Allegra (fexofenadine) was hiding or treating such a response, it may.

Possible: I the Allegra (fexofenadine) is taken for its anti-itch effect, stopping the medication may lead to an increase in itching. It is not withdrawl, it is the return of symptoms controlled by the medication.