The Old Friends Hypothesis

On his website, Professor Graham Rook gives a simple brief explanation of what is known about the link between exposure to our microbial world and its impact in sustaining health.

He asks the question “Is the term “Hygiene hypothesis” now obsolete? We argue that hygiene is not an important factor in the changes to our microbial exposures, so this misleading term should be replaced by "Old Friends Hypothesis" or the "Biodiversity Hypothesis"

He talks about the fact that we are not individuals, we are ecosystems with microbial partners (microbiota) that are involved in our development and how this situation appeared with the evolution of vertebrates about 500 million years ago when vertebrates evolved a complex immune system that is able to tolerate our many hundreds of species of microbial partners (microbiota), while simultaneously protecting us from pathogens. 

He also talks about why are our immune systems are attacking things they should not attack causing immune disorders and other health problems, and why these changes are occurring?

An important conclusion is that “domestic hygiene is not an important cause of the poor regulation of our immune systems that we see in high-income settings. Other lifestyle changes described in these pages are to blame”