The hygiene hypothesis and evolutionary medicine

The hygiene hypothesis is an explanatory model for increases in the incidence of chronic inflammatory disorders which have become much more prevalent in developed countries during recent last decades. Accumulating evidence indicates that some of this increased prevalence is due to defective regulation of the immune system resulting from diminished exposure to certain microorganisms that, co-evolving with mammals, influenced the evolution of their immune structures and functions all along the zootic scale up to primates. Understanding of the evolutionary causation of allergic and autoimmune diseases has already provided a better elucidation of their pathophysiology and has opened novel perspectives for their prevention. The hygiene hypothesis thus represents a typical, and possibly the most integrated, paradigm of evolutionary medicine. The recently proposed biodiversity hypothesis further extends the hygiene hypothesis, suggesting that the requirement for microbial input from the environment to promote immunoregulation is a major component of the beneficial effect of green space, and the microbiome constitutes a neglected ecosystem essential for human well-being. © Athens Medical Society