The Hygiene Hypothesis. Are we to clean for our own good?

Autoimmune and inflammatory diseases are on the rise. Are modern hygienic practices to blame and if they are should we start getting dirty again?

Good hygienic practice protects and promotes good health by breaking the vicious cycle of infectious disease. It has contributed to saving many millions of lives and is the basis of positive social and economic development and a better quality of life. The WHO has stated it has probably saved more lives than any other medical intervention. Infectious diseases with poor hygiene at their root of transmission continue to exert a heavy health toll. The need for cleanliness as well as having deep cultural roots may even be hardwired into our very DNA. In 1872 Darwin observed about our reaction to filth. “This visceral emotion is one of the main drivers of human behaviour. We recoil from the rotten, the stinking or anything that reminds us too strongly of death “. This ingrained adverse behaviour would have obvious evolutionary advantages. Being clean and hygienic is good for you.

But is being to clean making us ill? There is an old aphorism “A little dirt never hurt “and even “A little dirt does you good”. Some people believe our fixation with cleanliness is to blame for the rise in allergies such as hay fever, eczema, asthma and even with our food. That instead of protecting us our hygiene mania is playing mayhem with our health. There is some resonance of this belief in the Hygiene Hypothesis.  David Strachan’s original Hygiene Hypothesis dates from 1989. It was his attempt to explain the rapid 20th century rise in allergic diseases. The idea was that decreased infections in childhood due to overly clean hygienic practices led to a weaker immune system, this resulted in a wide range of autoimmune and inflammatory diseases due to lack of childhood exposure to harmful germs and fewer childhood infections.

This has more recently been developed as the Old Friend’s theory. That we have lost touch with good microbes and helminths, the "old friends", that mammals evolved alongside with when our immune system was still developing. It is thought that sanitary measures to protect us from infectious disease may have unintentionally cut us off from these good germs and symbionts. We had become so dependent on these old friends that our immune systems will not develop or function properly without them. What we have is a biodiversity problem not a cleanliness problem. This has led the Hygiene Hypothesis also being called the “Biome Depletion Theory"

There is some evidence of this in epidemiological studies into the so called Western world diseases. Rates of reported allergic, autoimmune, and other inflammatory diseases are rising in the industrialised world. These conditions are rare or absent in the developing world. It has been suggested that they increase in frequency with adoption of Western hygiene and sanitation standards. Correlation does not necessarily mean causation.  It is also argued that rising incidence of some of these diseases may be the result of lifestyle choices not least diet, and environmental changes. With less advanced health care systems they could also be going undiagnosed and underreported.

Whatever the merits of the case for or against the Hygiene Hypothesis giving up soap, hot water, decent sanitation and rolling in dirt will not help. I believe there is no strong evidence to support the idea that reducing modern practices of hygiene would have any impact on rates of chronic inflammatory and allergic disorders. Quite the contrary getting dirty doesn’t help our immune system and generally it makes any inflammation worse. Exposure to germs such as E. coli, Campylobacter, Salmonella, Norovirus, the Measles virus, and influencer can be very dangerous and can lead to life threatening illness. Deliberately exposing yourself to such germs by poor hygienic practice is simply plain foolish. It could also result in the need to increase antibiotic prescriptions.

There is a real risk that public awareness of the of the Hygiene Hypothesis and its misinterpretation may lead to people taking less notice of important hygiene education messages. We must not relax our standards, the need for infection prevention through good hygiene is as great as ever. There is compelling evidence that poor hygiene will lead to poor health.

 Effective hygiene and sanitation is a cornerstone of containing infectious disease threats and remains a national and global priority.

This article appeared in Environmental Health News . April 2017 Volume 32 Issue 3.