Still, the rise in allergies is too rapid to be explained solely by genetics. "The genetic pool can't change that much in such a short time," says Donald Leung, director of an allergy- immunology program in the U.S. "There have to be environmental and behavioral factors as well." Dozens of theories have blamed everyone from urban landscapers for favoring male plants (the ones that produce pollen), to women who don't breastfeed. Breastfeeding, the theory goes, confers greater protection against allergies.儘管如此,過敏症的上升速度太快,不能僅僅用遺傳學來解釋。美國過敏免疫學專案主任唐納德·梁(Donald Leung)說:"基因庫不可能在這麼短的時間內改變得那麼大。" “有是環境和行為的因素。”