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Too clean for our own good?

Date
The cleaner the better? Not necessarily.

The cleaner the better? Not necessarily. Photo: Alija

It's called the hygiene hypothesis: the idea that although a cleaner environment has improved our health in some ways, it's also messed with our immune system, contributing to increased allergy and autoimmune disease.

But it's not as simple as just being 'too clean', explains immunologist Professor Dianne Campbell, Chair of Paediatric Allergy and Clinical Immunology at The Children's Hospital at Westmead.

'It's less about clean kitchens and bathrooms and more about changes to living conditions – like less crowded housing, better public health measures, less infectious disease and less contact with large animals."  

"It's less about clean kitchens and bathrooms and more about changes to living conditions – like less crowded housing, better public health measures, less infectious disease and less contact with large animals. These have reduced our exposure to certain microbes in early childhood and this may have skewed our immune systems," she says.

The hygiene hypothesis sprang from 1980s research by British epidemiologist  David Strachan who was trying to understand why, when so many other diseases had been beaten by better sanitation, the rates of asthma and allergy were increasing in western countries – yet less common  in developing countries. One clue came from his study of 17,000 British children which found that those with a number of older siblings were less likely to have allergies. This raised interesting questions like could exposure to a broader range of microbes from mixing with other children in early childhood somehow protect against developing an allergy? Could it mean that young immune systems with more experience of dealing with a bigger variety of germs were better at telling the difference between a real threat and, say, a harmless speck of pollen?

Now a new twist to this theory has become a hot topic in science - the idea that changes to how we live have altered the kind of microbes inhabiting our gut, and it's this shift  in our gut microbes that's affecting our immune systems.

"We all have millions of gut microbes and their makeup is influenced by where and how we live – it varies depending on which country you live in or whether you live on a farm, for instance," Campbell says.

"But the effects of these changes to gut microbes is broader than just allergy. It's about how the immune system has been programmed from early in life which can also influence the chances of developing an autoimmune disease such as Type 1 diabetes or coeliac disease. However, it's unlikely that changes to the immune system are the sole cause of allergy and autoimmune disease – it's more likely to be an interplay of multiple factors like genetic susceptibility, what viruses you're exposed to early on, as well as diet in infancy."

In a perfect world we'd know how to populate the human gut with the right mix of microbes to help promote a healthy immune system – but we're not there yet.

"We still don't know what the best population of microbes is and other factors like the use of probiotics are still being investigated," Campbell says.

But while squeaky clean kitchens may have little to do with the increase in allergy, there's another way in which our fixation with super-cleanliness could eventually do more harm than good.

"There's evidence that repeated exposure to products containing household disinfectants – but not hospital grade disinfectants - makes bacteria more resilient and less susceptible to killing by both disinfectants and antibiotics," says microbiologist Cheryl Power of the University of Melbourne's Department of Microbiology and Immunology.

"This has implications for treating possible infections with these microorganisms because they may be harder to kill both in the environment and in people who are infected," she points out.

"I wouldn't argue with using anti-bacterials in hand washes, especially if someone is sick with gastro or a cold, but I would argue that their inclusion in many other products, such as dishwashing sponges, is not only unnecessary, but potentially counterproductive. For cleaning the kitchen, hot water and soap are just as effective as anti bacterial products."

49 comments so far

  • "We all have to eat a peck of dirt during our lives."

    The toxicity from long term exposure to some of the contents of this new generation of "essential" products not fully determined. However, that pales into insignificance compared to the horrible problem of rapidly emerging Multiple Resistance.

    Commenter
    Richard
    Location
    Melbourne
    Date and time
    March 02, 2014, 11:58PM
    • Gut microbe changes are effectively altering immune systems. This is old news.
      One of the easiest ways to protect your infant is of course with the transfer of gut flora from mother to baby through mother's milk. Chalk one more 'protective measure' up to 'mother nature' that a packet can't provide - the healthy gut flora of the mother is effectively and fully transferred to the infant directly through the mother's milk (not saying the b word so I don't get stupidly censored), so the baby gets an imprint, or genetic sample of the mother's own gut bacteria. This is the main way (for thousands of years) that diet in infancy has played a major role in adult later health. It is good to be mindful of these basic biological facts, and less panicky about the modern world

      Commenter
      Josie S
      Location
      Bondi
      Date and time
      March 03, 2014, 2:09PM
    • Josie S, while I agree that breast feeding does have benefits, it not the answer to the multiple resistance that Richard is talking about.

      Breast fed babies, just like bottle fed babies, can still get sick and can suffer more from illness than older people. Of course you know that. But don't you think, if babies can get reasonably sick from a fairly minor cold doesn't it make sense that they will suffer even more from a 'super bug' which would floor an adult? Of course they do, no matter what their diet.

      The answer to combating multiple resistance is to stop the general population from taking unnecessary antibiotics and from over-cleaning everything (as the article suggests).

      Commenter
      Judy
      Date and time
      March 03, 2014, 2:51PM
    • @Josie S, I agree with you that breast-feeding is a good thing but it does not have anything to do with transfer of gut microbes (there is no anatomical link between the gut and breasts). A major benefit of it is transfer of protective antibodies (notably IgA) - a new-born child has an undeveloped immune system and so transfer of IgA from milk to the child is beneficial.

      More generally, there are at least 10x more bacterial cells in a human body than there are human cells - there is increasing evidence that differences in this "microbiome" can have health outcomes - the fact that differences in the gut microbiome have been linked to risk of Autism Spectrum Disorder is just one example.

      This is a "hot topic" among biomedical researchers - it has led to the development of the Human Microbiome Project Consortium - this (somewhat technical but free-access) link describes it: http://www.nature.com/nature/journal/v486/n7402/full/nature11209.html .

      It is at the "basic science" stage at the moment but with a lot of hard work it may well lead to improved health outcomes.

      Commenter
      Dr Kiwi
      Date and time
      March 03, 2014, 4:15PM
  • This obsession and fear of 'germs' has been perpetuated by advertisers for decades and is one of the main contributors to the problems we are encountering with our immune systems. This marketed fear, created to sell products, is now entrenched in our psyche. We depend on certain bacteria to live in and on us for our survival. You don't need antibacterial wipes for the kitchen bench or special dishcloths when hot water with a bit of detergent will do the same job. Toilets don't need a cocktail of chemicals squirted up the rim and down the bowl, just a scrub and a wipe down with cheap white vinegar or weak bleach for stains. Soap and water is good enough for our hands and bodies. Foors just need to be clean and dry not so sanitised you could do surgery on them. Bacteria don't thrive on dry surfaces. No one sees it a problem to swallow a bottle of bacteria in fermented milk or yoghurt for gut health but everything else has to be nuked. It doesn't. It's only when a family member is infected with a contagious illness do you need to take extra precautions and only for the duration of the illness. Even halitosis wasn't an 'embarrassing medical condition' and a personal hygiene issue, not even a medital term until a company invented the word to spread the social fear of having bad breath and to sell its mouthwash.

    Commenter
    Jeff
    Location
    Melbourne
    Date and time
    March 03, 2014, 3:23AM
    • Glad to read a response that explores why we believe these products are essential. Marketing plays on unfounded fears and social exclusion, creating ideals that are possibly more unhealthy than accepting our bodies and environment in a less sanitised state. Obviously in hospitals, public areas, restaurants and homes where there are ill people we need to control the spread of infection, but in our everyday lives we are erroding our health with germ and smell phobias.

      Commenter
      LJanes
      Date and time
      March 03, 2014, 9:51AM
    • Recent medical show on ABC compared washing hands properly (vigorously) with soap and water compared to washing with the 99.999999999% germ killing washes showed that there was no significant benefit in terms of cleanliness of using the well marketed product.

      Commenter
      Public Joe
      Date and time
      March 03, 2014, 10:53AM
    • I saw that same doco @Public Joe. The researcher said that washing with common soap and water was actually more efficiacious than the bacterial washes in eliminating germs because of soap's mechanical action in removing grime.

      Commenter
      Jezz
      Date and time
      March 03, 2014, 2:27PM
  • Smaller families, urbanisation, and limited exposure to farm animals equals not enough endotoxins (in poo) in our lives as children.

    I also wonder about the effect of genetically modified crops. Our food has been altered for approx 25 years. These are the staples we feed our children from a vulnerable age. Perhaps their immune systems are not developing as they used to because the foods are so "sterile"?

    Commenter
    Peaches
    Date and time
    March 03, 2014, 7:26AM
    • No, you're off on the GM crop suggestion - probably from listening to anti-GM rhetoric. The food is not sterile - it's still a food product and not some chemicals thrown together with sugar and salt like so many products on our shelves.

      The staples we've been feeding our children for the past 10 000 years, like refined flour and sugar, loads of hormones injected into animals or anti-biotics in their food, the drugs we take and urinate into the environment, the choice of mothers not to breast feed, and the others mentioned in this article are all examples of how we've changed the environment in which the microbes our bodies interact with are selected for. By changing the way the microbes live we may be creating issues in the way that the immune system develops as it is a feedback loop initiated at birth.

      It would be very, very unlikely that GM foods, which are safe to consume, are the result of these events.

      I do find it funny how there is a general consensus to "trust the scientists" when it comes to the causes of global warming (almost a new faith system for some), yet it seems people are not willing to "trust the scientists" when it comes to GM food and are still wondering.

      Commenter
      Web
      Location
      Phloem
      Date and time
      March 03, 2014, 2:10PM

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