A Guide to the 4 Indoor Air Pollutants and Their Sources

Several indoor air pollutants can affect your quality of life at home, but what are the four major indoor air pollutants that contribute to poor indoor air quality the most?

In this article, we dive in-depth and discuss these four major pollutants, their source, and how the correct air filter can help reduce the level of these pollutants.

What Are the Symptoms of Poor Indoor Air?

There are a lot of particles in the air that can make you experience different symptoms, but we commonly tend to think of it as “seasonal sickness” or “indoor allergies.”

These terms make us think it’s all in our heads, and not as important as we’ve been led to believe. Fortunately, there’s a light of truth: sick building syndrome.

This syndrome has been recognized by the U.S. Environmental Protection Agency as a real phenomenon that is classified by an unexplainable illness, or acute health and comfort effects directly linked to someone’s time indoors.

Children, pets, immunocompromised individuals and the elderly will typically experience heightened or more severe symptoms of sick building syndrome.

Here are some of the symptoms of poor indoor air quality:

  • Irritation of the throat
  • Difficulty concentrating
  • Fatigue and irritability
  • Body aches and chills
  • Dry, itchy skin
  • Sneezing, wheezing and coughing
  • Burning sensations in the nostrils
  • Forgetfulness and brain fog
  • Headaches and dizziness

While this is not a comprehensive list, these are the most common ailments associated with poor indoor air quality and sick building syndrome. Many of these symptoms are associated with other ailments, which makes diagnosis of sick building syndrome difficult.

In addition to experiencing these symptoms, you may notice you feel better after you leave the environment for several hours, or while you are on vacation.  

What Are the Four Major Indoor Air Pollutants?

It’s impossible to defend your home against all indoor air pollutants. Some sort of air pollutant will always be present, whether it’s previous damage done to the inside of the home, or outdoor pollutants finding their way inside from open windows, cracks in the wall, or even from the brief environmental effects of opening your front door.  

Fortunately, the top four major indoor air pollutants can be avoided. (1) These pollutants are the top causes for allergies, illnesses and other ailments commonly associated with poor indoor air quality.

  1. Biological Pollutants
  2. Combustion Products

Did you know the appliances in your home can be a major cause of indoor air pollution? (2) Many people believe that if they keep their front door closed, they won’t need to worry about their indoor air; but, as we’ve seen so far, the two biggest contributors to poor indoor air quality come from inside the home.

Your appliances produce many combustible products, such as carbon dioxide, carbon monoxide, water vapor and nitrous oxides. With proper ventilation is working in top-notch conditions, these appliances should not be a problem.

When the home’s standard ventilation isn’t set up for a specific appliance, as can happen with remodels, or if the home’s ventilation fails, then it becomes a major problem. 

“If the appliance is not vented properly to the outside, or if the air pressure around a non-sealed gas appliance is negative enough to cause backdrafting, combustion pollutants can enter the house.” – SmarterHouse.org


Carbon monoxide is a particularly large concern, since the occupants are unable to smell, see or taste the gas. The only line of defense against this silent killer is carbon monoxide alarms, which require maintenance.

If your HVAC system is strong enough to handle a HEPA filter, it would filter out a lot of these products of appliance combustion, including exhaust from vehicles in your garage. Unfortunately, HEPA filters can only be used in higher-end air conditioning units, such as those found in factories and hospitals.

If your HVAC filter is no stronger than a residential system – and why would you need anything else – you can still filter out these harmful particles with a filter made from organic materials, such as CleanAir’s MERV 13 Allergen Destroyer air filter.

  1. Secondhand Smoke

We know that smoking causes lung cancer and can harm the smoker in a variety of ways. Pregnant and nursing women are advised against smoking because it’s known to hinder the development of their unborn children, and the elderly should avoid smoking because it can complicate pre-existing medical conditions.


“Secondhand smoke, classified by EPA as a Group A carcinogen, contains more than 7,000 substances.” – EPA.gov


Smoking doesn’t just affect the user, but also the people and animals around them. Smoking indoors around children, pets and the elderly is inconsiderate, but did you know that smoke can adhere to the walls and fabric in the room?

Toxic particles found in cigarette smoke can linger for years after it is initially introduced, slowly dissipating into the air around you. As these particles dissipate into the air, they are often breathed in by the inhabitants, causing allergies or other unwanted symptoms of illness.

While the best cure is prevention, you can still combat previous instances of indoor smoking by installing the proper air filter for your home and HVAC system and frequently changing the filter to keep it clean. The HVAC filter can trap particles released into the air within the woven cotton fibers.

  1. Mold

Mold can be caused by plumbing leaks inside the walls, indoor flooding and excessive moisture trapped inside the home. Unfortunately, Sheetrock is the perfect material for mold to grow on, providing a food source that can remain damp for extended periods. While it is growing, mold emits spores into the air. These spores float in the air, eventually settling in a place that is suitable for further growth.

Mold can cause a series of allergic responses, and may also be the cause of several household-borne respiratory ailments in the United States.

By upgrading your home air filter to a pleated MERV 8 filter or higher filter, you can trap several particles that would otherwise end up recycled through your home’s air system.

How Can I Improve the Air Quality in My Home?

You can improve the air quality in your home by using a pleated air filter design with a MERV rating of 8 or higher, depending on what your home’s heating and air-conditioning system can support.

The HVAC system is the home’s first line of defense against harmful air pollutants and the air filters should be changed regularly. For homes with multiple occupants and pets, or occupants with severe allergies, we recommend air filter replacement every 20 days. Otherwise, every 3 months is suitable for most home air systems.


“Children, pets, immunocompromised individuals, and the elderly will typically experience heightened or more severe symptoms of sick building syndrome.”

  • CleanAir

If you’re unsure of when your air filter needs to be changed, take a closer look at the loved ones who share your home.

When you join CleanAir’s air filter subscription service, you can choose the air filter that is right for your system and the frequency which the filters are delivered to your door.

All our filters ship for free, and if you can’t (or don’t want to) install it yourself, you can opt into our professional air filter installation service. You will never have to think about air filters again with CleanAir! That’s something to celebrate.


  1. S. Environmental Protection Service

  2. SmarterHouse