Open Air Factor

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By Craig Robinson


This webpage is a distillation of an article published in Caduceus Magazine, issue 108, written by Dr Richard Hobday, an independent researcher and author of Healing Sun: Sunshine and Health in the 21st Century - 1999 and Light Revolution: Health Architecture and the Sun - 2006.

You can subscribe to Caduceus here - just £20 for the year - Caduceus Subscriptions

You can order back issues here - Caduceus Back Issues

Dr Myhill has had articles published in Caduceus and the two most recent are:

  • Issue 106 - "GMC and CFS/ME :protecting psychiatrists and punishing patients"
  • Issue 109 - "General Medical Council: not fit for purpose"

An old idea

R.A. Cox et al recently (Sept. 2021] published an Opinion in "Atmospheric Chemistry and Physics", entitled Opinion: The germicidal effect of ambient air (open-air factor) revisited.

Full Citation - Cox, R. A., Ammann, M., Crowley, J. N., Griffiths, P. T., Herrmann, H., Hoffmann, E. H., Jenkin, M. E., McNeill, V. F., Mellouki, A., Penkett, C. J., Tilgner, A., and Wallington, T. J.: Opinion: The germicidal effect of ambient air (open-air factor) revisited, Atmos. Chem. Phys., 21, 13011–13018,, 2021.

This Opinion opened with the comment that:

The term open-air factor (OAF) was coined following microbiological research in the 1960s and 1970s which established that rural air had powerful germicidal properties

They go on to say that the germicidal properties of rural air had been:

attributed ... to Criegee intermediates formed in the reaction of ozone with alkenes. We have re-evaluated those early experiments applying the current state of knowledge of ozone–alkene reactions. Contrary to previous speculation, neither Criegee intermediates nor the HO radicals formed in their decomposition are directly responsible for the germicidal activity attributed to the OAF. We identify other potential candidates, which are formed in ozone–alkene reactions and have known (and likely) germicidal properties, but the compounds responsible for the OAF remain a mystery. 

They conclude by stating that it is:

of substantial interest to further investigate the role of ambient air in pathogen viability and the mechanisms behind the OAF.

Pine Forests

The air around pine forests was considered especially beneficial, leading to many sanatoria being constructed in pine forests - for example the King Edward VII Hospital in Midhurst, West Sussex, was surrounded by pines. This hospital has now been converted to flats. Pliny the Elder (AD23 - 79) mentions such in his Natural History, when recommending breathing air from woods with trees from which pitch and resin can be scraped off.

This idea has recently been re-inforced by ideas surrounding 'forest-bathing'.

See Visiting a forest, but not a city, increases human natural killer activity and expression of anti-cancer proteins, Q Li et al, 2008 where the authors conclude that:

The forest bathing trip significantly increased NK activity and the numbers of NK, perforin, granulysin, and granzyme A/B-expressing cells and significantly decreased the concentration of adrenaline in urine. The increased NK activity lasted for more than 7 days after the trip. 

Applicability to Covid-19

Dr Hobday and Peter Collignon have recently (2022) published An Old Defence Against New Infections: The Open-Air Factor and COVID-19 in which the authors call for more urgent research and make the point that:

As the COVID-19 pandemic has unfolded, it has become clear that person-to-person transmission occurs relatively rarely when people are outdoors. By contrast, infection risk appears to be greatly increased in poorly ventilated indoor spaces. In common with many other respiratory diseases, contracting COVID-19 is most often an 'indoor event'. The greater and quicker dilution and dispersal of infectious particles outdoors play a major part, but other factors contribute. Variations in temperature and relative humidity can inactivate coronavirus in the environment. Solar ultraviolet radiation inactivates coronaviruses and does so rapidly. The potential contribution of the open-air factor in the inactivation of coronavirus could be equally important. But this has not been investigated, despite robust evidence of its viricidal action.

Implications for Treatment Regimens

Already, Dr Myhill discusses the importance of sunshine and light in chapter 21 of our book Ecological Medicine - The Antidote to Big Pharma and Fast Foods. See also Vitamin D and Sunshine

The ideas concerning Open Air Factor only go to support the importance of "being outside". It does seem, for the time being, that the "rural" element is important.

This would especially be the case for anyone suffering with an acute infection, but also for those suffering with a chronic infection. So,

  • Add "being outside" in rural fresh air (maybe in a pine forest, if you are allergy-free) to your regimen as much as you can, and if able.
  • Consider forest bathing, if able.

CAVEAT - For those with ME, or other chronic illnesses, who are bedridden, or housebound, this will have to wait. Most of Dr Myhill's protocol is do-able for the severely affected. I was severely affected for a long period - 5 years bedridden, and a decade pretty much housebound, and so I do understand how very limiting ME can be. Please see here for details of the rest of the protocol - Overview of CFS/ME protocol

Historical References

Caduceus Magazine, issue 108, contains a fascinating review of the history of OAF. Below are some of the references, as included by Dr Hobday, in his piece.

The idea which ought to be uppermost in the minds of hospital committees, of architects, and of medical men, is that of pure air. The aggregation of a number of helpless sick and maimed under one roof, in a given space, without attention to this requisite may be at any time, as it has been, and now is, nothing but manslaughter under the garb of benevolence

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