2005/12/09 by Harald Renz, Nicole Blümer, Simona Virna +2 · 1 citation
Health Professions · Medicine · #Hygiene #Hygiene hypothesis #Immune system #Immunology #Medicine #Pathology #Pediatric health and respiratory diseases
paper · doi:10.1159/000090228
openalex publication_date 2005/12/09 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/30
The dramatic increase of allergic disorders in the last decades made their study an imperious demand. The increasing incidence of the development of allergic disorders seems to be associated with the modern westernized lifestyle, but causal reasons and the underlying mechanisms are far from being completely understood. Evidences suggest that priming of the immune responses against allergens happens already in utero. In addition, early life events are essential in shaping the immune answer towards the Th1- or Th2-profile, associated with a nonallergic or allergic phenotype, respectively. The hygiene hypothesis suggests that an early life environment rich in normal microbial flora primes the immune system in the Th1 direction towards clinical balance while a ‘sterile’ environment rather promotes the development of pathological immune phenotypes. In this review we collect epidemiological evidence for this concept. The data suggest an association between environment, lifestyle and the development of allergic diseases. This is the basis for the development of new hypotheses regarding the underlying pathomechanisms. The current view of cellular and molecular mechanisms underlying these phenomena includes fine-balancing between innate immune mechanisms and Th1, Th2 and regulatory T cells. These novel immunoregulatory events may explain the hygiene hypothesis by an interaction of environmental factors with innate immune mechanisms and various subtypes of T-cell responses.