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Too clean, or not too clean: the hygiene hypothesis and home hygiene
S F Bloomfield1, R Stanwell-Smith, R W R Crevel
1London School of Hygiene and Tropical Medicine, London, UK. Sally.Bloomfield@ifhhomehygiene.org
Summary
The hygiene hypothesis suggests reduced childhood infections increase atopic disorders. However, evidence links lifestyle changes and decreased microbial exposure, not just hygiene, to rising allergies.
Area of Science:
- Immunology
- Epidemiology
- Environmental Health
Background:
- The 'hygiene hypothesis' proposes reduced early childhood infections increase atopic disorders.
- The term 'hygiene hypothesis' has led to misinterpretations, with evidence not fully supporting a direct link to domestic hygiene.
- Rising allergic disorders do not correlate with decreased pathogenic infections or improved domestic hygiene.
Purpose of the Study:
- To critically evaluate the 'hygiene hypothesis' and its relationship to atopic disorders.
- To explore alternative explanations for the rise in allergic diseases.
- To clarify the role of microbial exposure in immune system development.
Main Methods:
- Review of existing epidemiological and immunological evidence.
- Analysis of the correlation between infection rates, hygiene practices, and allergic disease prevalence.
- Examination of proposed alternative hypotheses, such as microbial deprivation.
Main Results:
- The increase in allergic disorders does not directly correlate with decreased infections or improved domestic hygiene.
- Fundamental lifestyle changes leading to reduced exposure to microbes and helminths are implicated.
- The original formulation of the 'hygiene hypothesis' may be too narrowly focused on hygiene practices.
Conclusions:
- The relationship between hygiene practices and atopic disorders is not definitively proven.
- Reduced exposure to diverse microbial species is a more likely driver of increased allergies.
- Renaming the hypothesis to 'microbial exposure' or 'microbial deprivation' hypothesis could improve focus and avoid misinterpretations regarding hygiene.