Cleaning Indoor Air Can Limit Viral Exposure

Common consumer air purifiers can clear 99 percent of aerosols from a room in minutes
By Joseph Mercola
Joseph Mercola
Joseph Mercola
Dr. Joseph Mercola is the founder of An osteopathic physician, best-selling author, and recipient of multiple awards in the field of natural health, his primary vision is to change the modern health paradigm by providing people with a valuable resource to help them take control of their health. This article was originally published on
September 30, 2021 Updated: September 30, 2021

One strategy to reduce viral illnesses is to lower the concentration of viruses in the air, which may also improve health issues linked with indoor air pollution. Portable air purifiers, also known as portable air cleaners, are one of the easiest ways to accomplish that.

A recent study published by Cambridge University Press evaluated the use of portable air cleaners to reduce the aerosol transmission of viral disease, specifically COVID-19, in a hospital setting. At the start of 2020, many health experts believed that COVID-19 was spread only through droplet transmission, in much the same way that influenza is spread.

When a person with flu coughs, sneezes, or talks, droplets from their respiratory system can spread to others up to 6 feet away. These droplets can land on the mouths or noses of uninfected people, or land on a surface that a person may touch and then infect themselves by touching their own mouth, nose, or eyes.

In July 2020, a letter from 239 scientists petitioned the World Health Organization (WHO) to recognize the potential that SARS-CoV-2, the coronavirus that causes COVID-19, was also spread through aerosolized particles. The difference between droplets and aerosolized particles isn’t only in the size, but also in the potential that aerosol can travel on air currents, whereas droplets fall to Earth within 6 feet of release.

Shortly after the paper was published, the WHO reiterated its position that transmission is primarily from respiratory droplets that are expelled during a cough, sneeze, speech, or while singing. By November 2020, research published in the Journal of Korean Medical Science demonstrated that when there was direct airflow, transmission occurred over distances greater than 2 meters (6.5 feet).

One paper published in The Lancet in May listed 10 evidence-based reasons that the SARS-CoV-2 virus is primarily spread through an airborne route. As of May 7, the CDC states that most infectious sources for COVID-19 are closer than 6 feet.

However, the CDC also states that transmission risk may increase when an infectious person is indoors for more than 15 minutes, thus increasing the concentration of the virus in the air. The recent study from Cambridge University has implications for reducing the risk of transmission of viral respiratory particles in an enclosed space, such as in a hospital room or along hospital corridors.

Air Purifiers Reduce Aerosol Particles

paper published in Infection Control and Hospital Epidemiology in June 2020 suggested that using air purifiers in a dental office may act as a “supplementary protective measure.”

The authors cited a previous study published in 2010 that found using air purifiers in specific locations helped to significantly reduce aerosolized particles and reduce the amount of aerosol particles that health care workers were exposed to by up to 95 percent.

The scientists measured the filtration efficiency of two types of air filters and found those with a high-efficiency particulate air filter (HEPA) H12 class removed 83 percent of the aerosol and suggested that for dental procedures that generated a high amount of aerosols, a HEPA filter may help protect the health care workers.

The current study was performed in a tertiary care public hospital in Melbourne, Australia. Tertiary care involves specialized care using advanced and complex procedures, usually by specialists in a state-of-the-art facility. The researchers didn’t use aerosolized viral particles, but instead substituted glycerin-based aerosol to track the transmission from a patient room into the hallway and nurse’s station.

The researchers compared the clearance rates measured in the corridors with and without a HEPA filter over time. They found “With two small domestic air cleaners in a single patient room of a hospital ward, 99 percent of aerosols could be cleared within 5.5 minutes.”

“Air cleaners may be useful in clinical spaces to help reduce the risk of acquisition of respiratory viruses that are transmitted via aerosols. They are easy to deploy and are likely to be cost-effective in a variety of healthcare settings,” they concluded.

Cleaner Air May Slow Infection

The Environmental Protection Agency has also recommended the use of air cleaners and HVAC filters to help reduce the viral load in indoor areas, such as your home or business, especially when it’s difficult to get proper ventilation with outside air to help reduce airborne contaminants. The EPA stresses that ventilation and filtration are strategies to help reduce risk, but cannot by themselves stop the virus.

Portable air cleaners may be helpful when the outdoor air pollution is high, or the temperature and humidity would compromise health and safety. The EPA recommends air filters that can remove particles from 0.1 to 1 microns (micrometer).

To choose the correct unit, select one designed for the space in square footage and a unit with a high clean-air delivery rate (CADR) for smoke.

Some units are designed to remove pollen or dust, which are particles much larger than viruses. The second choice is a central furnace or HVAC filter through which the air in your whole home, office, school, and commercial building can be filtered. These typically are installed by an HVAC professional.

The EPA recommends considering a portable air filter to supplement a whole building filter when it’s difficult to achieve adequate ventilation. It’s also crucial for the filter to be changed as often as the manufacturer recommends for it to function properly.

Ventilation Versus Masks

In May, the CDC published a study in Morbidity and Mortality Weekly Report that found ventilation could lower the spread of COVID-19 by 39 percent in schools. By contrast, the incidence of COVID-19 was 37 percent lower when teachers and staff members were required to wear masks.

Some of the ventilation strategies used by the school systems included open windows and doors and using fans. When this was combined with HEPA filtration, it lowered the incidence by 48 percent.

Newer homes are airtight and energy-efficient. Higher efficiency comes with lower energy bills and a smaller carbon footprint. But the flip side of energy efficiency is a lack of ventilation, a danger of moisture buildup, and a greater potential for a buildup of indoor air pollutants.

The EPA has recommended that proper ventilation with outdoor air should be used to help reduce airborne contaminants, such as viruses. Use caution when using fans to help with ventilation around children. Position them out of reach of small children and ensure stability so they don’t fall. The EPA and CDC have several suggestions to help improve natural ventilation, including:

  • Open windows and screened doors as able.
  • Use a whole-house fan or evaporative cooler if you have one.
  • Open the outside air intake of the HVAC system if your system has one (not common).
  • Operate the bathroom fan when the bathroom is in use.
  • Avoid continuous ventilation with outside air when the outdoor air pollution count is high, or the weather is too hot, humid, or cold. Instead, open windows throughout the home for about 15 minutes each day.
  • If temperatures inside and outside are similar or there is little wind, you may need to use a fan or open windows on opposite sides of the house for cross ventilation.
  • You can improve ventilation by opening windows at different levels. For example, opening windows on different floors at the same time, opening the top sash of a double-hung window on one window and the bottom sash on another window.
  • If you don’t get enough air movement, consider using multiple fans to draw air in from one window and push air out through another.

Indoor Air Pollution Raises Health Risks

The clearance rate demonstrated in the featured study for aerosolized particles is encouraging since it has positive implications for protecting indoor air. The EPA finds that indoor air pollution is often two to five times higher than outdoor pollution, and occasionally is more than 100 times higher than outdoor levels.

Since most people spend 90 percent of their time indoors, it’s essential to engage strategies that help ventilate your house. According to the WHO, 90 percent of the world lives in areas where pollution is higher than is deemed safe.

Fine particulate matter that measures less than 2.5 micrograms (PM2.5) is one indicator of air pollution. This type of pollution is one of the most widely studied components and consists of particles that are up to 30 times smaller than the width of your hair.

Fine particulate matter can build indoors, raising your risk for several health problems. In one study of more than 20,000 people living in China, researchers found that exposure to toxic air triggered a reduction in intelligence.

Emerging evidence has shown PM2.5 can play a role in several diseases you may not have associated with air pollution, including diabetes, attention deficit hyperactivity disorder, autism, and sudden infant death syndrome.

Studies published in 2019 have also linked air pollution with mental health risks including psychiatric issues, anxiety, and depression. Using the same strategies of air purification and ventilation may also help reduce your exposure to indoor air pollution and is one strategy to help protect your overall health.

Tips to Lower Risk of Upper Respiratory Viral Illnesses

Beyond cleaning the air in your home, there are several specific strategies you can take to optimize your immune health and reduce your risk of respiratory illnesses and chronic disease.

Optimize your vitamin D.

I am passionate about the importance of vitamin D for your overall health and to strengthen your immune system. I recently published a peer-reviewed paper in Nutrients discussing the data demonstrating the importance of vitamin D to the risk of COVID-19. For more information, and links to the article in Nutrients, you can visit

Eat all your meals within a compressed window of time. 

Compress your eating window to six to eight hours. It may be somewhat challenging initially, but it’s a powerful strategy that will improve your immune function and help your body repair and regenerate. Begin slowly compressing the time until you reach six to eight hours, with the last time you eat at least three to four hours before going to bed. This creates a healthier metabolism.

Eat the right types of fat. 

Before processed foods became the norm for our diets, only 1 percent to 2 percent of your diet came from linoleic acid. However, currently, people are getting upward of 20 percent of their diet from linoleic acids, which are associated with damaging your metabolic health by damaging your mitochondria. Your body can store linoleic acid for years. It’s found in seed oils, such as sunflower, canola, safflower, and other vegetable oils.

Even healthy olive oil can have up to 20 percent of linoleic acid. However, most olive oils sold on the market today are adulterated and watered down with linoleic acid to lower the cost, which reduces the health benefit. Most restaurants use adulterated olive oil because pure olive oil is very expensive. Most restaurant food is also high in linoleic acid.

Make time to exercise. 

Your body is designed to move. By not providing stimulus, it may begin to decline, and you’ll lose muscle mass. This increases your potential for becoming frail. Although cardiovascular exercise is important, resistance training is just as important to building your muscle mass.

Try making a sauna part of your routine. 

Another form of exercise is using a sauna since it’s an exercise for your vascular system. Using a sauna is important as it activates your heat-shock proteins, which help to refold damaged proteins in your body.

Interestingly, 30 percent of the proteins in your body, when they are made, are misfolded. This means using a sauna is an important process to reduce your potential for neurodegenerative diseases, such as Alzheimer’s and Parkinson’s disease.

Dr. Joseph Mercola is the founder of An osteopathic physician, best-selling author, and recipient of multiple awards in the field of natural health, his primary vision is to change the modern health paradigm by providing people with a valuable resource to help them take control of their health. This article was originally published on