- Have a positive skin prick test [wheal (longest diameter) ≥ 3 mm greater than the negative control] at Visit 1 to any of the following perennial allergens: house dust mites (Dermatophagoides pteronyssinus and Dermatophagoides farinae), molds (Cladosporium cladosporioides, Alternaria alternata, Penicillium chyrsogenum (notatum), and Aspergillus fumigatus), or epithelia (cat, dog, and horse). In these cases, a careful history is to be taken and if moderate or severe symptoms are reported when exposed to the aforementioned allergens, the subject is to be excluded. Exception: the source of the allergen (cat, dog, horse) can be avoided for the entire study. Subjects with mild or no symptoms when exposed to the aforementioned allergens during the 3 years prior to Visit 1 will be allowed to enroll. Mild symptoms are defined as: sign/symptom clearly present, but minimal awareness, easily tolerated.