卫生假说（英语：hygiene hypothesis）是一种医学假说，指童年时因缺少接触传染源、共生微生物（如胃肠道菌群、益生菌）与寄生物，从而抑制了免疫系统的正常发展，进而增加了感染过敏性疾病的可能性。
This diagram simplifies the immune system into two separate tendencies: TH1 and TH2 responses. On the left, we see that exposures to germs, "dirt" and certain types of infection are part of the natural development of our immune response from a "default" TH2-based system at birth to a "mature" TH1-based system. On the right, we see how some cultural choices can interrupt the course of the immune system, and allow the TH2 response to continue to dominate and promote allergic conditions. Therefore, many of the advances of modernization, such as good sanitation and eradicating parasitic (helmith) infections, may actually be fueling this epidemic of allergies.
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a) 与皮肤屏障相关的基因突变使皮肤出现缺陷（水分流失，出现裂纹等），过敏原容易入侵，引起免疫反应。
b) 与免疫细胞受体/细胞因子相关的基因突变也影响免疫反应。
c) 环境因素
(3) 全景图：瘙痒抓挠引起皮肤进一步损伤，导致感染， 病情加剧。控制瘙痒非常重要。
（4）进一步的研究说明表皮结构分子 filaggrin 等 以及IL-22 在湿疹中的作用。前者说明过敏皮肤保湿的重要。后者要转换成疗法还有很长的路要走。
