Over the last 150 years, the prevalence of allergy, immunosuppression, antibiotic resistance, and infection (especially intestinal) has increased greatly, despite numerous public health measures. Rapid urbanization, modern childbirth and infant care practices, changes in dietary composition and food preparation, widespread antibiotic use, and changes in the ways we interact socially and with the natural environment all contribute to alterations in human immune regulation and microbiome composition. In the past, many well-meaning health interventions have interpreted “hygiene” to mean elimination of microbes. However,a more recent consideration of the available evidence calls for a more targeted approach to hygiene. In practice, this means preserving the immune-modulating value of early and regular exposure to commensal microbes while taking active steps to limit the spread of pathogens.
The authors state that “humans are ecosystems,” and that our immune systems require constant education about what is happening in our environments—most crucially during early childhood. Immune cells actively seek the training that comes from interaction with diverse microbes and molecules from our diets, the microbiomes of other humans, our pets, and from time spent outdoors. Gaining experience with a broad variety of relatively harmless microbes increases the immune system’s repertoire of organisms and molecular patterns that are tolerated. Of equal importance is that it aids recognition of pathogens that are distinct from previous encounters and that truly threaten health and homeostasis.
For this peer review, a panel of six experts discussed relationships among hygiene-related disease, reduced microbial exposures, microbiome composition, immune regulation and modern lifestyle changes. They developed this consensus paper as the result of their deliberations.
Redefining Hygiene for Immune Balance and Microbiome Restoration
These six experts in immune-related disease present hygiene and cleanliness as distinct notions—the former concerned with microbial balance rather than elimination. They propose a redefinition of hygiene in regards to human microbiome development and maintenance, with contributions from plant-rich diets, regular social and green space interactions, and a ‘targeted hygiene’ approach to individual and public health measures.