Even though allergen immunotherapy has been studied for more than a century, a great deal remains unknown about this commonly used treatment.¹ Immunotherapy, which is of benefit to the majority of appropriately selected patients, still largely relies on the injection of relatively crude allergen extracts, often involving doses that have not been rigorously studied.² The renewed interest in the study of immunotherapy over the past decade is encouraging and has resulted in important advances, including development of more refined allergens, assessment of different routes of delivery, and studies on the treatment of food allergy.