- Patients must have allergy to tree pollen allergen, defined by positive case history and positive skin prick test for tree pollen allergen (wheals of ≥ 5 mm (birch) and ≥ 3 mm (hazel and alder) greater than the negative control after skin prick testing) at Visit 1. Patients who will be skin tested at Visit 1 must adhere to the washout time for antihistamines.