Share this on:Copied!

There are many steps you can take to prevent respiratory infections. Thinking about indoor air quality is one of them.

Poor air quality can increase the risk of certain respiratory illnesses. These include COVID-19. It’s especially a concern in locations with a large number of people.

Examples of these include such schools and workplaces. They also include long-term care facilities.

Ventilation alone can’t prevent respiratory illnesses. But it can reduce your risk of exposure to the virus. It can complement a larger prevention strategy that includes hand hygiene and mask wearing. This can reduce exposure to the virus and vaccination to help your immune system prevent disease.

Learn more about the role of ventilation and air circulation in preventing airborne illness. Get indoor air quality tips for respiratory virus season.

Can Poor Ventilation Increase Your COVID-19 and Flu Risk?

Poor ventilation may increase your risk of COVID-19. It’s less of a concern with the flu, common cold, and respiratory syncytial virus (RSV).

Risk comes down to how the illnesses spread. Influenza, RSV, and SARS-CoV-2, the virus that causes COVID-19, primarily spread through respiratory droplets.

Most of these droplets are too heavy to remain suspended in the air. Instead, they drop to nearby surfaces.

Some SARS-CoV-2 droplets are light enough to remain suspended in the air for extended periods of time. A lack of air circulation can lead to infections.

“We don’t really worry about influenza staying in the air column and contaminating the room’s air for some time,” says Graham Snyder, MD, medical director, Infection Prevention and Hospital Epidemiology, UPMC. “But for SARS-CoV-2, it is a bit more likely to remain contagious in the air.”

A 2021 COVID-19 research review in Science reported “abundant evidence” for airborne transmission of SARS-CoV-2 and other respiratory viruses. Airborne transmission was most likely in poorly ventilated environments. The authors argued that adequate ventilation systems can reduce airborne transmission.

In another large-scale COVID-19 research project, researchers analyzed 150 Swedish classrooms. They found that more students and staff in classrooms with poor ventilation had higher numbers of SARS-CoV-2 infections than those in classrooms with better ventilation.

An October 2024 meta-analysis in The Journal of Infectious Diseases reported that the risk of SARS-CoV-2 transmission was highest in indoor settings where singing and exercise occurred. The authors wrote that better ventilation can reduce the risk of transmission.

However, although some SARS-CoV-2 particles can remain airborne, the majority do drop, Dr. Snyder says. Other pathogens — such as the tuberculosis bacterium or the measles virus — are more likely to stay airborne and infect people. Either way, better ventilation can play a role in limiting exposure when combined with other prevention methods.

“For SARS-CoV-2, it can remain suspended in the air, but not as much,” Dr. Snyder says. “And the virus isn’t as effective as spreading that way. So, air circulation is important, but up to a limit.”

How to Improve Ventilation

Organizations should ensure their HVAC systems provide at least the minimum outdoor air circulation requirement in accordance with ventilation codes. That’s according to the Centers for Disease Control and Prevention (CDC).

The CDC also recommends having at least five air exchanges per hour.

Ventilation that doesn’t circulate fresh air from outside can increase the risk of exposure to the virus. HVAC systems that don’t filter and recirculate air well enough can have the same effect.

This is especially true in high-occupancy spaces. Examples of these can include schools or long-term care facilities.

“If you’re a kid and you’re spending all day in a classroom and you’re coughing and sneezing in that classroom, there’s a good chance that somebody’s going to get (COVID) in that classroom,” Dr. Snyder says. “If you have no circulating air, you need to introduce some ventilation.”

Other natural ways to improve air circulation include opening windows and doors to increase outdoor airflow. Fans can also help.

The CDC says these tactics can complement ventilation systems. However, opening windows can get tricky during respiratory virus season, which runs from fall to early spring.

Do Air Purifiers Help Prevent Respiratory Illness?

Air purifiers can’t prevent airborne illnesses by themselves. They can help reduce airborne SARS-CoV-2 transmission indoors alongside other prevention strategies.

These can include mask-wearing and avoiding contact with people who are sick with respiratory infections. That’s according to the Environmental Protection Agency (EPA).

Air purifiers work by filtering contaminants out of the air and cleaning it. The EPA says that the best purifiers for respiratory health are those that capture particles under 1 micrometer in size. High-efficiency particulate air (HEPA) filters are 99.97% effective in removing particles that are as low as 0.3 micrometers in size.

Filtering the air can help with airborne particles. These particles can include dust, pollen, smoke, and other pollutants.

They can worsen conditions like asthma and chronic obstructive pulmonary disease (COPD). But the virus research remains mixed.

A 2022 study in mSphere reported that an air cleaner with a HEPA filter was effective in removing SARS-CoV-2 from the air. But a 2024 study in JAMA Network Open reported that there was no significant difference in respiratory infections. That study compared residents of an aged-care facility who had HEPA purifiers in their rooms with those who didn’t.

Another JAMA Network Open analysis in 2025 reported that HEPA filters alone didn’t decrease respiratory virus exposure. The authors wrote that HEPA filters may help in schools with poor ventilation. But other environmental interventions are likely still necessary to reduce overall viral exposure.

Examples of these inventions include improving air circulation and maintaining humidity levels between 40% and 60%.

“(The air purifier) basically has to be next to you or between you and the other person for it to work,” Dr. Snyder says. “It’s not going to work if you put it in the corner. It has to have more proximity.”

The EPA says the best places for an air purifier are a bedroom or a living room or anywhere else people spend most of their time. Someone who is vulnerable to respiratory illness or isolating with a respiratory disease can place the purifier wherever they spend most of their time.

Do masks help against respiratory illness?

Face masks can also protect against respiratory viruses in crowded areas with poor ventilation.

A 2021 CDC study reported that masks reduced exposure to airborne particles by 72%. Masks reduced exposure to airborne particles by up to 90% when combined with a HEPA filter air cleaner.

How to Reduce Airborne Virus Spread at Home

The CDC recommends the following tips to potentially lower your risk for airborne virus spread at home:

• Open windows and doors — Opening them at both ends of the house can improve air circulation. Even opening them a small crack can help.
• Regularly change your HVAC system air filters — The CDC recommends pleated air filters on your HVAC system. It also recommends changing them every three months or according to the manufacturer’s instructions. The CDC also recommends changing the fan from “Auto” to “On” when you have visitors.
• Use an air purifier — A HEPA air cleaner can help reduce potential particles in the air.
• Use fans — Exhaust fans and other fans can improve air circulation.

The CDC says a portable CO2 monitor can keep you informed about indoor air quality. Readings above 800 parts per million indicate you should increase air circulation.

Air circulation alone won’t prevent respiratory viruses. But it may help reduce their spread. It can complement other ways of preventing airborne and surface respiratory virus transmission.

Other steps you can take to avoid cold, flu, RSV, and COVID-19 transmission include:

• Getting recommended vaccines.
• Staying home when you’re sick and isolating from others.
• Washing your hands frequently with soap and water or hand sanitizer.
• Wearing masks.