Allergy rises not down to being too clean, just losing touch with old friends
16 October 2012
Professor Graham Rook, also co-author of the report, who developed the ‘Old Friends’ version of the hypothesis, says “the rise in allergies and inflammatory diseases seems at least partly due to gradually losing contact with the range of microbes our immune systems evolved with, way back in the Stone Age. Only now are we seeing the consequences of this, doubtless also driven by genetic predisposition and a range of factors in our modern lifestyle - from different diets and pollution to stress and inactivity. It seems that some people now have inadequately regulated immune systems that are less able to cope with these other factors.”
Dr Stanwell Smith explains the probable reasons why this has happened “since the 1800s, when allergies began to be more noticed, the mix of microbes we’ve lived with, and eaten, drunk and breathed in has been steadily changing. Some of this has come through measures to combat infectious diseases that used to take such a heavy toll in those days - in London, 1 in 3 deaths was a child under 5. These changes include clean drinking water, safe food, sanitation and sewers, and maybe overuse of antibiotics. Whilst vital for protecting us from infectious diseases, these will also have inadvertently altered exposure to the ‘microbial friends’ which inhabit the same environments”.
But we’ve also lost touch with our “old friends” in other ways: our modern homes have a different and less diverse mix of microbes than rural homes of the past. This is nothing to do with cleaning habits: even the cleanest-looking homes still abound with bacteria, viruses, fungi, moulds and dust mites. It’s mainly because microbes come in from outside and the microbes in towns and cities are very different from those on farms and in the countryside.
“The good news”, says Professor Bloomfield “is that we aren’t faced with a stark choice between running the risk of infectious disease, or suffering allergies and inflammatory diseases. The threat of infectious disease is now rising because of antibiotic resistance, global mobility and an ageing population, so good hygiene is even more vital to all of us.”
“How we can begin to reverse the trend in allergies and CID isn’t yet clear”, says Professor Rook. “There are lots of ideas being explored but relaxing hygiene won’t reunite us with our Old Friends - just expose us to new enemies like E. coli O104.”
“One important thing we can do”, says Professor Bloomfield, “is to stop talking about ‘being too clean’ and get people thinking about how we can safely reconnect with the right kind of dirt”.
IFH has also produced a general fact sheet and Q&A on issues related to immunity to infectious disease, allergies and the hygiene hypothesis is available here>
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- The International Scientific Forum on Home Hygiene (IFH) is a not-for profit, non-governmental organisation which is working to develop and promote home hygiene practice based on sound scientific principles
- Professor Sally Bloomfield is also Chairman of IFH
- Dr Rosalind Stanwell-Smith is Honorary Senior Lecturer at the London School of Hygiene and Tropical Medicine
- Professor Graham Rook is from the Centre for Clinical Microbiology, University College London, UK
- The “Old Friends hypothesis” as developed by Rook in 2003, proposes that the microbial exposures vital for immune regulation are not the infectious diseases (respiratory infections such as colds, influenza, measles etc. and gastrointestinal infections such as cholera, polio, Campylobacter, norovirus etc.), which have evolved and spread over the last 10,000 years as we came to live in ever denser urban communities, but rather the microbes with which we co-evolved, and that were already present in Paleolithic, hunter gatherer, times – the era when the human immune system was developing, in close association with the abundant microbes present in that era. Put simply, in the same way that we have evolved to become dependent on Vitamin C in our diet (something which most mammals could, and most non-primates can still, synthesise for themselves) because it became plentiful in our food, we have also evolved dependency on microbial exposure, such that our immune systems cannot now function properly without it. It is hypothesised that the “old friends” include commensal organisms (the normal microbiota of the skin, gut and respiratory tract of humans and animals) and some potentially pathogenic organisms such as helminths (worms), which establish chronic infections or carrier states. These latter have to be tolerated, because attempts by the immune system to eliminate infections that it cannot remove only lead to pointless tissue-damaging inflammation. The OFs also include environmental saprophytes i.e. species which inhabit our indoor and outdoor environments. Other scientists are now suggesting that we need constant exposure to a diverse range of old friends, not just specific microbes. The most likely explanation of this need for daily exposure to microbes, particularly in early life, is because they interact with the regulatory systems which keep our immune system in balance. Without this our immune systems may overreact, or react inappropriately, or fail to switch off completely when no longer needed, which is an underlying cause of these diseases.
- Antibiotics are relevant here because there is evidence that they affect immunoregulation by reducing the diversity of gut microbiota.
- Microbiological studies show that routine daily or weekly cleanliness habits have no sustained effect in reducing levels or altering the types of microbes in our home environment. Frequent showering and bathing might be a contributing factor, but there is no good evidence of a link, other than in worsening an existing risk of eczema. The idea that we could create a ‘sterile’ environment in our homes through excessive cleanliness is just not credible: as fast as they are removed by cleaning, the microbes in our homes are being replaced, via dust and air from the outdoor environment, by microbes that are constantly shed from the human body and from our pets and from contaminated foods and other items brought into our homes