Abstract
SummaryThe ‘hygiene hypothesis’ as originally formulated by Strachan, proposes that a cause of the recent rapid rise in atopic disorders could be a lower incidence of infection in early childhood, transmitted by unhygienic contact with older siblings. Use of the term ‘hygiene hypothesis’ has led to several interpretations, some of which are not supported by a broader survey of the evidence. The increase in allergic disorders does not correlate with the decrease in infection with pathogenic organisms, nor can it be explained by changes in domestic hygiene. A consensus is beginning to develop round the view that more fundamental changes in lifestyle have led to decreased exposure to certain microbial or other species, such as helminths, that are important for the development of immunoregulatory mechanisms. Although this review concludes that the relationship of the hypothesis to hygiene practice is not proven, it lends strong support to initiatives seeking to improve hygiene practice. It would however be helpful if the hypothesis were renamed, e.g. as the ‘microbial exposure’ hypothesis, or ‘microbial deprivation’ hypothesis, as proposed for instance by Bjorksten. Avoiding the term ‘hygiene’ would help focus attention on determining the true impact of microbes on atopic diseases, while minimizing risks of discouraging good hygiene practice.
Highlights
When a disease, or group of diseases, rises rapidly without a specific explanation, it stimulates investigation to identify the cause, so that preventive measures can be devised
It is only recently that infectious disease (ID) specialists have entered the debate, concerned that publicizing the idea that we might be ‘too clean’ could have a detrimental impact on the public’s perception of ID risks in the home and elsewhere, and of the importance of controlling such risks. In response to these latter concerns the International Scientific Forum on Home Hygiene commissioned a review of the hypothesis, in order to consider the implications it might have for hygiene, hygiene in the domestic setting
The rapid increase in allergic asthma and other atopic disorders in the industrialized world is usually considered to have started between 1960 and 1970 with progressive rises during the 1980s and ‘90 s, Isolauri suggests that there has been a steady rise in sensitization to aeroallergens since the 1920s [3]
Summary
Correspondence: Sally Bloomfield, Morningside, Willow Green Lane, Little Leigh, Northwich, Cheshire CW8 4RB, UK. The increase in allergic disorders does not correlate with the decrease in infection with pathogenic organisms, nor can it be explained by changes in domestic hygiene. This review concludes that the relationship of the hypothesis to hygiene practice is not proven, it lends strong support to initiatives seeking to improve hygiene practice. It would be helpful if the hypothesis were renamed, e.g. as the ‘microbial exposure’ hypothesis, or ‘microbial deprivation’ hypothesis, as proposed for instance by Bjorksten. Avoiding the term ‘hygiene’ would help focus attention on determining the true impact of microbes on atopic diseases, while minimizing risks of discouraging good hygiene practice
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