Because today's environment is too sterile, type 1 immune responses (against infectious disease or tumors) are triggered relatively rarely, but type 2 immune responses are increasingly common. As a result, the slightest environmental disturbance can provoke an immune response and exacerbate an allergic condition.
因為環境太乾淨的結果，第一型免疫（針對感染疾病或腫瘤的抵抗力）較少被激發，於是越來越低，相對地第二型免疫的活性就越來越高，結果環境中任何一點風吹草動都會引發激烈的反應，反倒造成過敏疾病加重。