More than 50 million Americans are affected by various types of allergies each year. Paired with the recent rise in pollen counts across much the United States, it seems like there’s never been a better time to consider investing in an air filter. But what exactly are air filters and are they really the right solution to help ease or prevent symptoms of various respiratory diseases? To answer some of the most common questions surrounding these devices, we asked the opinion of three different medical experts: Alana Biggers, MD, MPH, a board-certified internal medicine physician; Stacy Sampson, DO, a board-certified family medicine physician; and Judith Marcin, MD, a board-certified family medicine physician.

Here’s what they had to say.

Alana Biggers: Allergens from the air include:

  • dust
  • dirt
  • pollen
  • mold and mold spores
  • fibers and lint, metal
  • plaster or wood particles
  • hair and animal fur
  • bacteria
  • other microorganisms

Stacy Sampson: There are invisible particles in the air that you can’t see with the naked eye, and these particles may cause irritation to the body in some way. This can include coughing fits, a runny nose, sneezing, nausea, headaches, or even allergic reactions. Over time, inhaling irritating substances could cause long-term problems in your respiratory system and other body systems.

Judith Marcin: The quality of indoor and outdoor air can be affected by two main types of substances: particles and gas.

Indoor air quality is commonly affected by particles such as dust, pet dander, pests such as cockroaches and rodents, and viruses. Gases tend to be carbon monoxide, smoke, cooking fumes, and chemical fumes. These types of substances can cause a variety of reactions from mildly allergic to potentially life-threatening.

Outdoor air quality is affected by particles such as pollution, construction dust, ash, exhaust and outdoor allergens, like tree pollen and grasses. Gases accumulate from things such as burning coal or diesel, car exhaust and industrial waste. Some useful measures of outdoor air quality include the Air Quality Index and pollen count.

Over time, both indoor and outdoor substances can cause inflammation that leads to permanent lung injury, causing conditions such as chronic obstructive pulmonary disease (COPD) and pulmonary fibrosis. Indoor and outdoor pollution and allergens can also aggravate allergies and asthma.

AB: Air is filtered when it’s brought back through a unit to be conditioned and then redistributed. In a car, the air filter prevents dirt, debris, and impurities from getting into your engine and dust, pollen, dirt, and other pollutants from getting into your air and heat vents.

SS: The air filter allows the air from your heater and air-conditioner to pass through to the duct system in your home, while at the same time trapping the small particles in the air in hopes of not letting them pass through to the rest of the house. This allows the air passing through your ventilation system to have less of a chance of spreading around irritants that can be inhaled.

JM: The types of air filters people most commonly use in their homes are known as mechanical air filters. These are filters for use in an HVAC system. Disposable filters need to be replaced and systems cleaned at regular intervals. Mechanical air filters work by trapping particles from the air onto the filter. High efficiency particulate air (HEPA) filters are a type of high efficiency mechanical filter. While mechanical home filters can trap everything from dust to cockroach allergens and pet dander, they don’t trap gases.

AB: Yes, air filters can help filter out allergens that can be a trigger for people with respiratory issues, such as asthma or COPD.

SS: Yes, especially if they have any type of preexisting respiratory problems like asthma, COPD, or allergies. Air filters can be beneficial in reducing the risk of acute respiratory attacks by trapping irritants that try to pass into the ducts of the ventilation system, allowing you to breathe easier.

JM: Unfortunately, it’s not been consistently shown that improving air quality through filtration alone will help improve allergy or asthma symptoms. This is likely due to the fact that larger allergens often aren’t easily airborne, so they can’t be filtered. Instead, they settle on surfaces. Regular dusting, vacuuming, washing sheets, and keeping hard surfaces clean are the best ways to control these larger particles. Many experts recommend a combination of methods to control allergies and asthma that includes a cleaning routine, mechanical filters, and portable air cleaners. It is, however, recommended to avoid portable air cleaners or other electronic air cleaning systems that produce ozone, which is known to be a lung irritant.

AB: Not all filters treat air particulates the same. The higher-grade filters are more expensive, but filter very small particulates. The benefits of these may outweigh the costs, especially if you have allergies or a respiratory issue.

SS: Yes, the benefits outweigh the cost. When looking at the cost of a visit to an emergency room or a physician’s office for an examination, mixed with the cost and side effects of potential medication for respiratory related issues, an air purifier is definitely a smart investment in comparison. If you have a home with multiple inhabitants that could have breathing problems because of a dirty air filter, buying a filter every few months may end up being cheaper than having multiple people needing to see the doctor at one time.

JM: A 2011 review of studies on air filters and air cleaners shows that a MERV 12 filter did improve asthma symptoms in one of the studies they evaluated. Overall, these experts concluded that a combination of medium to high efficiency filters, combined with portable room air cleaners in sleeping areas seem to offer the best symptom relief for the cost.

AB: Filters operate on a minimum efficiency reporting value (MERV rating) with a range of 1 to 20. The higher the rating the higher the amount of air particulates the air filter can filter. There are, however, some suggestions that believe authentic HPEA filters are rated between 17 and 20.

SS: There are different rating systems from filter to filter and even from brand to brand. Once you know the size of filter you need, either comparing different filters in person or online will help you become familiar with the available options and price ranges. Some filters will be rated for filtering out more types of particles than others. With the MERV rating system, generally the higher the number rating, the greater number of smaller particles it can filter from the air. However, depending on the age of your HVAC system, the higher MERV rated filter may also block the air from effectively being able to travel through the filter, which may be harder in terms of wear and tear on your furnace or AC system. A knowledgeable associate at a home improvement store or HVAC company should be able to provide helpful assistance when looking for the right air filter to install.

JM: The MERV system grades the quality of mechanical filters on a 1 to 20 scale based on what it can filter. The system was designed by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers:

  • Grade 1
    to 4
    (low efficiency) is designed to protect the HVAC system but not to
    improve air quality.
  • Grade 5
    to 13
    (medium efficiency) can remove a range of small to large particles
    from the air including viruses, some molds, pet dander, and bacteria. Not as
    useful against dust mites. Grades 7 to 13 function at a level close enough to
    high efficiency filters for most indoor allergens.
  • Grade 14
    to 16
    (high efficiency) are the best standard filters available. They can
    remove very small particulates of 0.3 microns or larger.

AB: In my opinion, air filters work to remove air particulates. They may be most helpful for people with allergies or respiratory issues. Air filters don’t take away all air particulates and don’t prevent people from getting sick. Portable air filters may help in one room but will not help an entire home. Portable air filters are also limited in what they can filter.

SS: Yes, air filters work to reduce the amount of potentially harmful microparticles one could breathe in from the air. This can prevent environmental allergies, and other respiratory problems from developing and symptoms from occurring.

JM: Air filters do work to trap particles, but it’s important to understand what they’re filtering. While these mechanical filters do trap small to large particles, studies have not been able to prove that effective filtering alone actually improves asthma or allergy symptoms.

Much of this has to do with the fact that larger allergen particles settle on carpeting, surfaces, and bedding rather than circulating through the air. The evidence indicates that combining medium to high efficiency air filters with a portable air cleaner used in the sleeping room, along with a regular cleaning routine are the best ways to manage asthma and allergy symptoms.

Dr. Alana Biggers is a board-certified internal medicine physician. She graduated from the University of Illinois at Chicago. She’s an assistant professor at the University of Illinois at Chicago College of Medicine where she specializes in internal medicine. She also has a master’s of public health in chronic disease epidemiology. In her spare time, Dr. Biggers likes to share healthy living tips with followers on Twitter.

Dr. Judith Marcin is a board-certified family physician. She graduated from the University of Illinois at Chicago. She’s been a graduate medical educator for the past 15 years. When she’s not writing or reading, she enjoys traveling in search of the best wildlife adventure.

Dr. Stacy Sampson is a board-certified family medicine physician. She graduated from Des Moines University College of Osteopathic Medicine in Iowa. She has experience in utilization management and hospital medicine and is a volunteer physician at a free clinic. She likes to spend time with her family and is a hobbyist musician.