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Is the hygiene hypothesis an example of hormesis?
John A Bukowski1, R Jeffrey Lewis
1ExxonMobil Biomedical Science, Inc., 1545 Route 22 East, P.O. Box 971, Annandale, NJ 08801-0971.
Nonlinearity in Biology, Toxicology, Medicine
|March 31, 2009
Summary
The hygiene hypothesis suggests early microbial exposure prevents allergies. While infections show mixed results, general microbial exposure, especially gut microbes, appears protective, potentially via hormesis.
Area of Science:
- Immunology
- Epidemiology
- Microbiology
Background:
- Rising incidence of allergic disorders in developed countries.
- The hygiene hypothesis proposes microbial stimulation shifts immune response from Th2 (allergy-promoting) to Th1 (allergy-fighting).
Purpose of the Study:
- Review evidence linking early life microbial exposures to atopic disorders.
- Evaluate if this association suggests a hormetic effect.
Main Methods:
- Systematic review of studies on infections, parasitic burdens, and microbial exposures.
- Analysis of associations with atopic disorder development.
Main Results:
- Inconsistent evidence for bacterial/viral infections protecting against allergies.
- Chronic parasitic infections show protection but with pathology; light burdens may worsen allergies.
- Consistent evidence suggests general microbial exposures, particularly gut commensals, are protective against allergy development.
Conclusions:
- General microbial exposures may align with the hygiene hypothesis via a hormetic effect.
- Further research with rigorous prospective designs is needed to confirm timing, dose, and route of exposure.
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