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Food, Health, and Eco-news
Outdoor Air in the Viral Age
An old idea – exposure to sunshine and fresh air as a way to lower infectious disease risk – is getting a close look in the age of COVID-19 05/01/2020 By Brad Lemley

The COVID-19 pandemic has mobilized the world’s top researchers to create cutting-edge tests, treatments and vaccines. But simple, low-tech measures, revealed by a careful study of history, may also be vitally important – especially during this dangerous period when we wait for months, or even years, for those high-tech efforts to pay off.

The devastating “Spanish flu” outbreak of 1918-1919, which killed between 50 million and 100 million worldwide, revealed a remarkable fact: the simple act of being outdoors, exposed to fresh air and sunshine, appeared to have a strong therapeutic effect – it both limited infections, and helped the infected recover faster. (Hobday et al 2009).

Patients who were housed in an open-air hospital in Boston “were spared the worst of the outbreak” researchers noted. Indeed, the combination of fresh air and sunshine, combined with careful hygiene and reusable cloth facemasks “appears to have substantially reduced deaths among some patients and infections among medical staff.” (Hobday et al 2009)

Fresh Air and TB

This echoed studies from the late 19th century that suggested the tuberculosis bacterium could be reduced or eliminated by fresh air blowing through the rooms of patients. As Dr. Arthur Ransome, a leading tuberculosis investigator, wrote, “… abundant fresh air, together with sunshine, acts antiseptically upon both the bodies and the clothing of patients, destroying all organic impurities which may emanate from either, and so purifying the air that enters the respiratory organs.” (Hobday 2019)

To exploit this “purifying” effect, hospitals in the first half of the 20th century were built with large, openable, south-facing windows to permit flooding rooms with sunlight and fresh air (Hobday 2019).

However, by the 1950s, chemical disinfectants largely replaced the open-air treatment ethic. The common belief that fresh air could disinfect both viruses and bacteria was largely forgotten.

The Coronavirus and the Outdoors

But we are starting to remember.

New research suggests a hallmark of SARS-CoV-2, the virus that causes the disease COVID-19, is that it also spreads more readily indoors.

“Rapid person-to-person transmission of COVID-19 appears likely to have occurred in healthcare settings, on a cruise ship, and in a church,” noted a recent study on outbreak patterns. Infection clusters were “associated with closed environments” such as fitness centers, restaurants and hospitals (Frieden et all 2020).

Conversely, in a review of Japanese data, the odds for transmission in “open-air environments” were a remarkable 18.7 times lower (Frieden et all 2020).

Why the virus seems to be inhibited by outdoor environments is not entirely clear, but it appears that some combination of warm temperatures, sunlight and very low or high humidity are generally hostile to its spread.

It’s also possible that those who spend time outside have higher blood levels of vitamin D, and that this both inhibits infection and disease severity (Grant WB et al 2020).

Bottom Line

There’s clearly been plenty of confusion among both the public and lawmakers regarding just what constitutes effective “social distancing.” In the early days of the pandemic, outdoor recreation areas were closed nearly as readily as indoor ones.

But both old and new research suggest that those outdoor environments are safer, all else being equal, than those indoors.

"Ninety percent of our lives in the developed world are spent indoors in close proximity to each other," lamented Yale immunobiologist and senior author Akiko Iwasaki, noting the unfortunate consequence of indoor viral spread. (Hathaway B, 2020)

So take a lesson from history.

Even when outdoors, keep your distance from strangers to at least six feet as recommended by the Centers for Disease Control, but get out there! (“Social Distancing, Quarantining and Isolation” 2019).


Hobday RA, Cason JW. The open-air treatment of pandemic influenza. Am J Public Health. 2009;99 Suppl 2(Suppl 2):S236–S242. doi:10.2105/AJPH.2008.134627

Hathaway B. Hopes of pandemic respite this spring may depend upon what happens indoors. YaleNews. Published April 1, 2020. Accessed April 17, 2020.

Hobday R. The open-air factor and infection control. Journal of Hospital Infection. 2019;103(1). doi:10.1016/j.jhin.2019.04.003.

Frieden TR, Lee CT. Identifying and Interrupting Superspreading Events—Implications for Control of Severe Acute Respiratory Syndrome Coronavirus 2. Emerging Infectious Diseases. 2020;26(6). doi:10.3201/eid2606.200495.

Grant WB, Lahore H, Mcdonnell SL, et al. Evidence That Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Deaths. 2020. doi:10.20944/preprints202003.0235.v2.

Social Distancing, Quarantine, and Isolation. Centers for Disease Control and Prevention. Published April 4, 2020. Accessed April 29, 2020.