An allergenic protein that has been found to be clinically significant in over 50% of a population of patients allergic to that particular allergen. Major allergens have been characterized for a number of allergenic species. Common examples of major allergens include: Amb a 1 (Ragweed), Fel d 1 (Cat), Phl p 5 (Timothy grass), etc. Characterization of major allergens has not been completed for a number of allergenic species.