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What Is The Hygiene Hypothesis?

Today is the second time I ever hear about this "Hygiene Hypothesis" thingy. As usual I had to look it up on wikipedia.

So what does this hypothesis state?

"In medicine, the hygiene hypothesis states that a lack of early childhood exposure to infectious agents, symbiotic microorganisms (e.g. gut flora), and parasites increases susceptibility to allergic diseases by modulating immune system development."

Where did this hypothesis come from?

"First proposed by David P. Strachan in an article published in the British Medical Journal, the hygiene hypothesis was developed to explain the observation that hay fever and eczema, both allergic diseases, were less common in children from larger families, which were presumably exposed to more infectious agents through their siblings, than in children from families with only one child.

The hygiene hypothesis has been extensively investigated by immunologists and epidemiologists and has become an important theoretical framework for the study of allergic disorders. It is used to explain the increase in allergic diseases that has been seen since industrialization, and the higher incidence of allergic diseases in more developed countries. The hygiene hypothesis has now expanded to include exposure to symbiotic bacteria and parasites as important modulators of immune system development, along with infectious agents."

Is there any evidence?

Apparently there is:

• "The hygiene hypothesis is supported by epidemiological data. Studies have shown that various immunological and autoimmune diseases are much less common in the developing world than the industrialized world and that immigrants to the industrialized world from the developing world increasingly develop immunological disorders in relation to the length of time since arrival in the industrialized world.
  
• Studies have also shown that in young unvaccinated children, who also suffer from measles, less allergic diseases are present.
  
• Studies in mice have shown that exposure of young mice to viruses can result in a decreased incidence of diabetes"
  

Are there any medical applications for this?

Yes there are:

• "The use of infectious organisms, specifically helminths, to treat the types of disease described by the hygiene hypothesis is being studied in the UK, USA and Australia.
  
• Because of the promise shown by this research two versions of what is now commonly referred to as Helminthic therapy, using Trichuris Suis Ova and Necator Americanus, have become available."
  

Read more on wikipedia

Interesting?

Richard Dawkins Interviews Randolph Nesse

Randolph Nesse is the author of "Why We Get Sick: The New Science of Darwinian Medicine"

"Why, in a body of such exquisite design, are there a thousand flaws and frailties that make us vulnerable to disease?..."

Amazon's review: "Is our tendency to "fix" our bodies with medicine keeping them from working exactly as they're supposed to? Two pioneers of the emerging science of Darwinian medicine argue that illness is part and parcel of the evolutionary system and as such, may be helping us to evolve towards better adaptation to our environment."