What to know about the AC units in your home, as well as air conditioning in your office, restaurant, gym, or other public spaces.

By Claire Gillespie
May 21, 2020
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Now that warmer weather is on the way and lockdown orders are being lifted, people are wondering: Can air conditioning spread COVID-19, especially the AC in public place, like your office or a restaurant?

Early research raised concerns. A recent study, published in Emerging Infectious Diseases, found that nine people in Wuhan, China (the first epicenter of the new coronavirus outbreak) were infected with the virus simply by sitting near an air conditioning vent in a restaurant. According to researchers, the virus was spread by one asymptomatic diner who sat at a table in front of the AC unit. Four people at the table later tested positive for COVID-19, as did five people at neighboring tables. 

Manish Butte, PhD, an associate professor in the department of microbiology, immunology, and molecular genetics at the University of California, Los Angeles, tells Health that within a public setting, like a restaurant, workplace, or gym, air conditioning might be potentially risky. It has to do with the way AC works. Air conditioning circulates air more rapidly, which removes humidity. Water vapor can hold onto heat, so with less of it in the air once the humidity is removed, a room or space cools down. “Less humidity in the air promotes evaporation, which causes droplets in the air to dry up and disappear,” says Butte. 

It helps to understand a little about droplets—the particles (containing mostly water, but also any pathogens our bodies may be infected with, such as the new coronavirus) that we expel when we breathe, talk, cough and sneeze. A single cough releases about 3,000 droplets, while a single sneeze can release about 30,000, according to a blog post that went viral written by Erin Bromage, a comparative immunologist and professor of biology specializing in immunology at the University of Massachusetts Dartmouth.

Different actions produce different sizes of droplets, which can travel varying distances. When an AC unit is turned on, air flow from the vent pushes these droplets through the air and potentially into other people. “The air flow direction is what matters,” adds Butte. 

Bromage believes that indoor spaces with ventilation systems and lots of people (such as the restaurant in the Wuhan study) are concerning from a transmission standpoint. And Butte agrees that air conditioning can definitely make droplets containing infectious virus particles spread farther. Remember, while air conditioning might make a room feel fresher on a warm day, it’s simply recycled existing air.  

When it comes to the Wuhan restaurant study, it’s important to take into account that it had a small sample size and didn’t replicate conditions in a lab. “I don’t necessarily think that this study is representative of transmission risk,” infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security in Maryland, tells Health. “However, it is important to be mindful of air flow patterns, especially if they are strong and create a jet stream for droplets.” 

So should we all be ditching our air conditioning systems until the threat of COVID-19 has passed? In a word, no. Air conditioning in your own home is far less risky than AC in a busy public place, if you’ve been practicing social distancing measures and following all other recommendations regarding hygiene. If you haven’t had a stream of people in and out of your home, the only droplets that could be spread by air conditioning are those from you and whoever you’ve been in lockdown with. “Within a home, where everyone is highly exposed to each other, there isn’t a need to worry about air conditioning,” says Butte.

As for air conditioned offices, malls, and restaurants, know that a risk exists, but most experts are not saying that you should refrain from venturing into public places. As lockdown eases, spending time in any indoor space outside your home requires a certain level of risk assessment. If you do go to a restaurant or any other busy place with air conditioning, continue to practice social distancing, be vigilant about hand-washing and not touching your face, and, as always, stay home if you feel sick or have symptoms of COVID-19.  

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDCWHO, and their local public health department as resources.

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