The most effective ways to get rid of germs in indoor air are improving ventilation, using air filtration, and controlling humidity. Most airborne pathogens, including viruses and bacteria, travel in tiny particles smaller than 5 microns that can stay suspended indefinitely under normal indoor conditions. That means they linger until something actively removes or neutralizes them.
Why Airborne Germs Linger Indoors
When someone coughs, sneezes, or even just breathes, they release particles loaded with pathogens. Studies measuring cough aerosols from people with respiratory infections consistently find that the majority of pathogens end up in particles smaller than 5 microns. For influenza, 87% of viral particles in exhaled breath were found in particles smaller than 1 micron. These tiny particles don’t settle to the ground like dust. They float in still indoor air for hours, drifting through rooms and accumulating in poorly ventilated spaces.
Particles in this size range are also the ones that reach deep into your lungs when inhaled, which is exactly why reducing their concentration matters.
Bring In More Fresh Air
Ventilation is the simplest and most immediate tool you have. Every time fresh outdoor air replaces stale indoor air, it dilutes the concentration of airborne pathogens. The CDC and NIOSH recommend aiming for at least 5 air changes per hour (ACH) in indoor spaces. A Lancet Commission report grades ventilation quality on a scale: 4 ACH is “good,” 6 is “better,” and anything above 6 is “best.”
Five air changes per hour won’t guarantee perfectly clean air, but it significantly reduces your exposure to viral and bacterial particles. In practical terms, here’s how to increase air exchange at home or in a small office:
- Open windows on opposite sides of a room. Cross-ventilation creates airflow that pushes contaminated air out and pulls fresh air in. Even partially open windows help.
- Run exhaust fans. Bathroom and kitchen exhaust fans pull air out of your home, forcing replacement air in through any openings.
- Use your HVAC system’s fan setting. Setting the fan to “on” instead of “auto” keeps air circulating through your system’s filter continuously, not just when heating or cooling kicks in.
Choose the Right Air Filter
Filtration physically traps airborne particles, including those carrying bacteria and viruses. The key is matching your filter to the size of what you’re trying to catch.
HEPA filters capture 99.97% of particles at 0.3 microns, which is actually the hardest particle size to trap. Anything larger or smaller gets caught even more efficiently. Since most airborne pathogens ride on particles between 0.5 and 5 microns, a true HEPA filter handles them with ease. Portable HEPA air purifiers are the most accessible option for most homes.
If you have a central HVAC system, upgrading your furnace filter makes a big difference. MERV ratings measure a filter’s ability to catch particles of different sizes:
- MERV 8 (the standard in most homes) catches essentially zero particles in the 0.3 to 1.0 micron range and only about 20% of particles between 1 and 3 microns.
- MERV 13 catches over 50% of particles in the 0.3 to 1.0 micron range, over 85% between 1 and 3 microns, and over 90% of larger particles.
One study found that upgrading from MERV 8 to MERV 13 filters was the single most impactful change for reducing airborne particle exposure, more effective than any other control method tested. Before upgrading, check that your HVAC system can handle the increased airflow resistance of a higher-rated filter. Most systems built in the last 15 years can handle MERV 13 without issues, but older units may strain.
Size Your Air Purifier Correctly
A portable air purifier only works if it’s powerful enough for the room it’s in. The number to look for is the Clean Air Delivery Rate, or CADR, which tells you how many cubic feet of air the unit can clean per minute. Harvard’s School of Public Health recommends sizing your purifier to deliver at least 4 to 6 equivalent air changes per hour in your specific room.
A rough formula: multiply your room’s square footage by the ceiling height to get cubic feet, then multiply by your target ACH and divide by 60. That gives you the minimum CADR you need. For a 200-square-foot bedroom with 8-foot ceilings targeting 5 ACH, you’d want a CADR of at least 133. Most manufacturers list CADR on the box or product page. Place the purifier where air can circulate freely around it, not tucked behind furniture or in a corner.
Keep Humidity Above 40%
Humidity plays a surprisingly large role in how far and how long airborne germs travel. Research conducted in classroom-sized spaces found that raising relative humidity above 40% at normal room temperature (around 73°F) substantially reduced the number of viable viral particles detected at every distance measured. Below 40% humidity, viral particles traveled farther and remained infectious in much higher numbers. Above 40%, viable counts dropped to a narrow, low band.
This happens for two reasons. Higher humidity causes small airborne particles to absorb water, grow heavier, and fall out of the air faster. It also degrades the outer structure of many viruses more quickly. During winter, when indoor humidity often drops to 20 or 30%, running a humidifier to maintain 40 to 60% relative humidity helps reduce airborne pathogen levels. Stay below 60% to avoid encouraging mold growth.
UV-C Light for Continuous Disinfection
Ultraviolet light in the UV-C range, particularly around 254 nanometers, damages the genetic material of bacteria and viruses so they can no longer reproduce. UV-C devices designed for air disinfection work by exposing air to this light as it passes through or near the unit. The most effective wavelength for killing germs is 262 nanometers, and the low-pressure mercury lamps used in most consumer and commercial devices produce light at 254 nanometers, which is close enough to be highly effective.
The catch is exposure time and distance. UV-C intensity drops rapidly with distance, following the inverse square law: doubling the distance between the lamp and the target quadruples the time needed for disinfection. This means UV-C works best in enclosed devices where air is forced past the lamp at close range, or in upper-room installations where a layer of UV light continuously treats air near the ceiling as it naturally circulates upward. Portable UV-C air purifiers that combine filtration with UV exposure offer the best of both approaches.
For safety, the National Institute for Occupational Safety and Health limits direct UV-C exposure to 6 millijoules per square centimeter over an 8-hour period. Properly designed consumer units keep the UV light contained so you’re never directly exposed.
What About Ionizers and Houseplants?
Bipolar ionization devices generate charged particles that supposedly cluster around pathogens and destroy them by forming reactive molecules on their surfaces. The technology exists in many newer HVAC systems and standalone units. However, the actual mechanisms behind ionization’s germ-killing ability haven’t been clearly established, and a major limitation of existing studies is that they were conducted in small test chambers, often funded by the device manufacturers, where ozone levels weren’t adequately controlled. Some ionizers produce ozone as a byproduct, and OSHA limits ozone exposure to 0.1 parts per million over 8 hours, while the EPA sets an even stricter limit of 0.05 ppm for indoor devices. If you choose an ionizer, verify it’s been independently tested and produces ozone well below these thresholds.
Houseplants are often suggested as natural air purifiers. One frequently cited study found that indoor plants reduced airborne microbes by about 50% compared to plant-free spaces. But there’s an important gap: no studies have directly tested whether plants reduce virus survival or transmission. The evidence so far covers bacteria and fungi only, and the conditions in controlled experiments don’t always reflect real rooms with real airflow. Plants may contribute modestly to air quality, but they’re no substitute for mechanical filtration or ventilation.
Maintaining Your Filters
A clogged filter stops working. Pre-filters, which catch larger particles like dust and pet hair before they reach the main filter, typically need replacement every 3 months. Activated carbon filters, which handle odors and volatile chemicals, last about 6 months. The HEPA filter itself generally lasts about a year under normal use. These timelines vary by manufacturer and how heavily you run the unit, so check the product specifications for your model. Running a purifier with an overdue filter can actually reduce airflow enough to make the device ineffective, while still drawing power.
For HVAC filters, check them monthly and replace them when visibly dirty. MERV 13 filters in a residential system typically last 60 to 90 days, though homes with pets or high dust levels may need more frequent changes.
Combining Methods for the Best Results
No single strategy eliminates all airborne germs. The CDC’s 5 ACH target can be met through any combination of ventilation and filtration added together. For example, if your natural ventilation provides 2 air changes per hour and a portable HEPA purifier adds another 3 equivalent air changes, you’ve hit the target. Layering ventilation with filtration and humidity control addresses germs through three different mechanisms simultaneously: dilution, physical removal, and reduced viability. That combination is far more reliable than relying on any one approach alone.