The Hygiene Hypothesis and its Implications for Home Hygiene, Lifestyle and Public Health

This report reviews the scientific and epidemiological evidence relating to the ‘Hygiene Hypothesis’, and examines the implications for hygiene and our overall relationship with the microbial world we live in. The ‘Hygiene Hypothesis’, originally postulated in 1989, proposed that a lower incidence of infection in early childhood, transmitted by unhygienic contact with siblings, could be an explanation for rising levels of allergic diseases. It was suggested that this “infection” exposure no longer occurs because of higher standards of household and personal cleanliness - that “we have become too clean for our own good”. New knowledge is now challenging this interpretation.

Although microbial exposures are vital for immune regulation, the “Old Friends” hypothesis suggests that the required “exposures” are not to infectious diseases (IDs), but to environmental, and human and animal commensal microbes. This concept has now also been applied to a range of disorders such as multiple sclerosis, type 1 diabetes and inflammatory bowel disorders. New data suggests that altered exposure results from a range of measures vital to protecting us from IDs, but which have inadvertently reduced or altered exposure to the microbial friends that regulate our immune systems. These include food and water quality, sanitation and environmental cleanliness together with medical advances such as the introduction of vaccines, or antibiotic usage.

Since the need for infection prevention is as great as ever, we need to tackle both issues – reversing the trend in CIDs and reducing the burden of ID. There is need for clearer communication about the Hygiene Hypothesis and guidance on how to target hygiene practices effectively where and when they are required. This review was prepared by the authors and was then submitted for detailed review by Dr Renè Crevel and Mr John Pickup.