Monday 30 August 2021

Challenging the hygiene hypothesis


In medicine, the 'hygiene hypothesis' states that early childhood exposure to particular microorganisms protects against allergic diseases by contributing to the development of the immune system.


However, there is a pervading view (public narrative) that Western 21st century society is too hygienic, which means toddlers and children are likely to be less exposed to germs in early life and so become less resistant to allergies.


Exposure to microorganisms in early life is essential for the 'education' of the immune and metabolic systems. Organisms that populate our guts, skin and airways also play an important role in maintaining our health.


There has been a public narrative that hand and domestic hygiene practices, that are essential for stopping exposure to disease-causing pathogens, are also blocking exposure to the beneficial organisms.


Recent research looks at four factors.


1.      The microorganisms found in a modern home are, to a significant degree, not the ones that we need for immunity.

2.      Vaccines, in addition to protecting us from the infection that they target, do a lot more to strengthen our immune systems, so we now know that we do not need to risk death by being exposed to the pathogens.

3.      We now have concrete evidence that the microorganisms of the natural green environment are particularly important for our health; domestic cleaning and hygiene have no bearing on our exposure to the natural environment.

4.      Recent research demonstrates that when epidemiologists find an association between cleaning the home and health problems such as allergies, this is often not caused by the removal of organisms, but rather by exposure of the lungs to cleaning products that cause a type of damage that encourages the development of allergic responses.


To prevent spread of infection, cleaning needs to be targeted to hands and surfaces most often involved in infection transmission. By targeting our cleaning practices, we also limit direct exposure of children to cleaning agents




Graham A.W. Rook, Sally F. Bloomfield. Microbial exposures that establish immunoregulation are compatible with targeted hygiene. Journal of Allergy and Clinical Immunology, 2021; 148 (1): 33 DOI: 10.1016/j.jaci.2021.05.008


Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (

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