title: Asthma and the hygiene hypothesis. Does cleanliness matter?
abstract: BACKGROUND
  The early hygiene hypothesis explained the development of allergies by a lack of infections; nowadays, the aspect of excessive cleanliness in affluent populations seems to have replaced this concept. Yet, no investigation has shown that home or personal cleanliness relate to allergic diseases.
  
  
  OBJECTIVE
  To relate personal and home cleanliness to risk of asthma and allergies.
  
  
  METHODS
  Comprehensive questionnaire information on home or personal cleanliness and allergic health conditions at school age was collected in 399 participants of the urban Perinatale Asthma Umwelt Langzeit Allergie Studie (PAULA) birth cohort. Bacterial markers were assessed in floor and mattress dust and were related to cleanliness and allergic diseases.
  
  
  RESULTS
  Personal cleanliness was inversely related to bacterial compounds on floors and mattresses, whereas home cleanliness effectively reduced dust amount but not microbial markers. Exposure to muramic acid related to a lower prevalence of school-age asthma (adjusted odds ratio, 0.59 [95% confidence interval, 0.39; 0.90]). Mattress endotoxin in the first year of life was inversely associated with atopic sensitization (0.73 [0.56-0.96]) and asthma at school age (0.72 [0.55-0.95]). Despite the associations of dust parameters both with cleanliness and allergic health conditions, the development of allergies was not related to home and personal cleanliness.
  
  
  CONCLUSIONS
  Bacterial exposure in house dust determined childhood asthma and allergies. Personal cleanliness, such as washing hands, and home cleanliness were objectively reflected by dust parameters in homes. However, neither personal nor home cleanliness was associated with a risk for asthma and allergies. Other microbial components in house dust not affected by personal hygiene are likely to play a role.
authors.affiliation: 1 Dr von Hauner Children's Hospital, Ludwig Maximilians University of Munich, Munich, Germany.
authors.forename: Juliane
authors.initials: J
authors.lastname: Weber
authors.forename: Sabina
authors.initials: S
authors.lastname: Illi
authors.forename: Dennis
authors.initials: D
authors.lastname: Nowak
authors.forename: Rudolf
authors.initials: R
authors.lastname: Schierl
authors.forename: Otto
authors.initials: O
authors.lastname: Holst
authors.forename: Erika
authors.initials: E
authors.lastname: von Mutius
authors.forename: Markus J
authors.initials: MJ
authors.lastname: Ege
mesh_terms: D001249:Asthma / Q000276:immunology*; D004391:Dust / Q000032:analysis / Q000276:immunology; D004731:Endotoxins / Q000032:analysis; D006801:Humans; D006920:Hygiene; D061148:Hygiene Hypothesis; D006967:Hypersensitivity / Q000276:immunology; D008019:Life Style; D009112:Muramic Acids / Q000032:analysis; D018570:Risk Assessment
chemical_list: D004391:Dust; D004731:Endotoxins; D009112:Muramic Acids
keywords: allergies; childhood; endotoxin; house dust; muramic acid