Hygiene Hypothesis: Fact or fiction.

This reports an appraisal of some evidence for the hygiene hypothesis. It used ten established epidemiological criteria to rate the validity of some of the main causal relationships of the current hygiene hypothesis research (endotoxins, common colds, gastrointestinal tract flora and pathogens, and autoimmunity). One conclusion is that there are opposing causal relationships between microbial exposure and diseases. Journal of Allergy and Clinical Immunology 2003;111:471-8.