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Module 2 - How does microbial exposure protect us from allergies and other chronic inflammatory diseases?

The link between microbial exposure and immune diseases

The concept of a link between reduced microbial exposure and the rise in  allergic disease was  first proposed by David Strachan in 1989 and was named the  Hygiene Hypothesis. 

Although the basic concept still appears to be correct, the proposal of a link to infectious disease and hygiene is now largely discounted. Refinements to the original hypothesis now offer a more plausible explanation.

The Old Friends (OF) Mechanism

The Old Friends mechanism was proposed by Graham Rook in 2003.

He proposed that the required microbial exposures are not infectious diseases (colds, flu, measles, norovirus etc) which evolved only over the last 10,000 years, but the microbes we co-evolved with in hunter gatherer times when the human immune system was developing.

Although these microbes are still there, through modern lifestyle changes we have lost our exposure to them.

The hygiene hypothesis has been variously renamed as:

  • The Old Friends Mechanism, 
  • Microbiome Depletion Hypothesis,
  • Microbial diversity hypothesis

Evolved dependency on microbial exposure.

Our immune systems have become so dependent on these exposures that they cannot function properly without them.

Learn more about the Old Friends mechanism