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'Hygiene is more than keeping our living environment clean'

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Sally Bloomfield wonders how to restore confidence in hygiene, wrongly dismissed by some as an ’obsessive cleanliness’ responsible for a range of chronic diseases such as allergies and autoimmune conditions

Microbiome science shows that microbes inhabiting human bodies constitute an organ as essential to our health as the liver and kidney – and that failure to sustain a diverse microbiome by interaction with our microbial world is associated with chronic diseases including allergies, autoimmune diseases and type 1 diabetes. This is prompting worrying media headlines suggesting “we need to stop washing our hands” as a means to build a healthy gut microbiome. This builds on the erosion of confidence in hygiene stemming from the hygiene hypothesis – proposed in 1989 – that children who have more infections are less likely to develop allergies.

Although evidence still supports the theory that microbe interactions are essential to our health, the term ‘hygiene hypothesis’ is misleading and dangerous. No good evidence suggests hygiene, as the public understands it, is responsible. Evidence shows exposures we need, particularly in early life, are the diverse range of mostly non-harmful microbes from our living and natural environment. Public health strategies most likely to sustain a healthy microbiome include healthier diets, reduced antibiotic prescribing, increased outdoor exposure and promoting natural childbirth and breast feeding. The idea that obsessive cleanliness is the culprit is no longer supported.

For those of us who recognise the importance of hygiene, not least because of its role in tackling antibiotic resistance and protecting the rising numbers of people who are vulnerable to infection, the question is how to restore confidence in it.

We need to understand that hygiene is something more than “keeping our living environment clean”. It is based on understanding the key routes (hands and surfaces) of infection transmission, and targeting hygiene practices in the places and at the times that matter to break the “chain of infection”, particularly times associated with food, respiratory, hand and toilet hygiene, and healthcare. Hand hygiene is central to all these activities, so any “stop washing hands” message is a highly irresponsible approach.

Crucially, change will not happen without altering public, public health and professional perceptions. First, the terms ‘hygiene hypothesis’ and ‘germs’ must be abandoned. ‘Germs’ (traditionally used to instil fear) should not be used to describe ambient surface contamination, which carries little infection risk. We need to develop a balanced appreciation of our microbial world – the essential role it plays in our health as well as its potential dangers. Because we are brought up to imagine these invisible creatures as slimy and disgusting, this represents a real challenge. We must also change misconceptions about hygiene and cleanliness – that ‘dirty’ does not necessarily mean presence of harmful organisms – nor does visible cleanliness mean their absence.

In future we are all going to have to view our microbial world very differently.

Sally Bloomfield is honorary professor at the London School of Hygiene and Tropical Medicine and chair of the International Scientific Forum on Home Hygiene

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