Illustration: Kieran Blakey

The Nuance

The Germ-Cleaning Power of an Open Window

Let the breeze blow those pathogens away

Published in
5 min readApr 9, 2020


AAnyone who’s been cooped up in a stuffy, stagnant room can appreciate the simple pleasure of an open window and a fresh breeze. Breathing clean outdoor air may even provide some cognitive benefits: If a space is small and poorly ventilated, there’s evidence that accumulated C02 can cause drowsiness, poor concentration, and other symptoms.

More importantly, open windows can prevent viruses and other pathogens from spreading. A 2019 study in the journal BMJ Infectious Diseases found that windows and other sources of natural ventilation can reduce the transmission of tuberculosis by 72%. And in developing countries, where expensive ventilation systems are not affordable, hospitals often rely on open windows and fans to encourage indoor-outdoor air exchange.

In the midst of the Covid-19 crisis, public health officials in the U.S. are increasingly trumpeting the benefits of open windows and fresh air. The Centers for Disease Control and Prevention (CDC) recommends opening windows to reduce the spread of coronaviruses, and state health departments are encouraging the same measures to slow the transmission of Covid-19, specifically.

“Changing the room air is a widely used measure for infection prevention and control,” says Stephen Morse, an infectious disease researcher and professor of epidemiology at Columbia University’s Mailman School of Public Health. “It replaces any virus-contaminated air with clean air.” Opening windows is one of the easiest and cheapest ways to encourage this type of air turnover, he says.

According to a 2009 World Health Organization report on illness transmission and air ventilation, people expel microscopic droplets of saliva while coughing and sneezing, and also while talking and exhaling. Once expelled, these droplets can quickly evaporate — leaving behind nearly weightless airborne particles. These particles can house illness-causing pathogens, and they can ride on the airflow created when a person opens or closes a door or walks from one room to another. While the likelihood that these airborne particles will make somebody sick is uncertain and may vary from one pathogen to the next, that WHO report found that poor…



Markham Heid

I’m a long-time contributor at TIME and other media orgs. I write mostly about health. I grew up in Michigan, but these days I live in southwest Germany.