No clinical evidence base to support the hygiene hypothesis

Abstract

KEYWORDS Clinical evidence;Allergy; Hygiene hypothesisSummary The hygiene hypothesis is a popular explanation for recent increases in allergy in the western world. This hypothesis suggests that development of allergy (or asthma) could be prevented by exposure to immune stimulants such as viruses, bacteria and endotoxins, in particular in the prenatal period or early childhood. How evidence-based are the observations which support the hygiene hypothesis? All clinical epidemiological indications in favour of the hypothesis are based on observational (cross-sectional and cohort) studies and not on observations in randomised controlled intervention studies. In cross-sectional studies no causal relationships can be assessed with sufficient validity. Also in cohort studies there are validity problems, as the exposure is not determined by chance (by means of randomisation) and could be influenced by behaviour. And behaviour might well be a confounder, since it can be associated with both exposure and outcome. A problem is that, without being appropriately tested in well designed prospective research, the hygiene hypothesis has currently already become so popular in the news media that an increased occurrence of asthma might even be induced as a result of an increased exposure. Although the currently available evidence to support the hygiene hypothesis is poor, it appears that the hypothesis has to some become a matter of faith or ideology. Scientists should take care that messages imparted to the general public do not go beyond or conflict with existing evidence. © 2004 General Practice Airways Group. Published by Elsevier Ltd. All rights reserved.General practitioners and other health care providers are in receipt of conflicting information on the pathopysiology of allergy (and asthma), especially in relation to the hygiene hypothesis. It is difficult for these health care professionals to translate this information into practical advice for their patients who want to know how to avoid the development of these diseases in their children. 1

Allergische Erkrankungen

“…In der Hygienehypothese finden sich Ansätze zur Erklärung des Anstiegs allergischer Erkrankungen in entwickelten Ländern sowie für Prävalenzunterschiede in verschiedenen Bevölkerungsgruppen. Die Hygienehypothese ist jedoch nicht unumstritten, zumal sie nicht in konsistenter Weise durch wissenschaftliche Evidenz gestützt wird [39,40,41,42,43] und den heutigen Hygienestandards durchaus auch positive Effekte auf die Gesundheit zugeschrieben werden können [44].…”

Global and Regional Trends of Multiple Sclerosis Disability-Adjusted Life Years Rates: A 25-Year Assessment

“…Based on hygiene hypothesis first formulated by Strachan [43] in 1989 and summarized by Yazdanbakhsh et al [44], human immune system may change inappropriately by improving hygiene, vaccination, and the use of antibiotics in developed countries. Some investigations have been consistent with this hypothesis, [45,46] whereas others offered evidence that was equivocal or contradictory [47][48][49]. Although the hygiene hypothesis has its own proponents and is very popular, the opponents of this hypothesis claim that all investigations in favor of hygiene hypothesis are observational studies.…”

“…Although the hygiene hypothesis has its own proponents and is very popular, the opponents of this hypothesis claim that all investigations in favor of hygiene hypothesis are observational studies. Thus, causal relationships cannot be inferred [49]. According to our literature review, all studies conducted on MS DALY rates are mainly descriptive or cross-sectional.…”

The hygiene hypothesis: promises and pitfalls

“…Gore, Custovic, van Schayck, and Knottnerus for a lively and thoughtful debate on this hygiene hypothesis [2][3][4][5]. I join them in that much of the current epidemiological data are not strong enough to infer causation.…”