Last Updated on March 3, 2026
How often do you reach for a tissue because of a lingering cough?
How often do your eyes burn inside your own home?
Most people assume outdoor pollution is the problem.
In reality, indoor air can contain higher pollutant concentrations than outdoor air.
Considering most Canadians spend close to 90% of their time indoors, indoor air quality directly impacts daily health.
Summary
Indoor air quality refers to the condition of air inside buildings and its impact on occupant health. Poor indoor air quality is commonly caused by inadequate ventilation, biological contaminants such as mold and dust mites, volatile organic compounds from furnishings, combustion byproducts, and excess humidity. Since people spend approximately 90% of their time indoors, prolonged exposure to indoor air pollutants may contribute to respiratory irritation, fatigue, headaches, and worsening asthma symptoms. Improving indoor air quality involves proper ventilation, humidity control between 35% and 50%, filtration upgrades, source removal of contaminants, and professional air quality assessment when symptoms persist.
Key Takeaways
- Key causes include poor ventilation, biological contaminants, and indoor pollutants.
- Symptoms of poor indoor air quality vary but can include throat, eye, and nose irritation, skin issues, respiratory problems, and fatigue.
- Diagnosing air quality issues starts with checking the ventilation system for adequate fresh air supply.
- Improving air quality aims to prevent health issues, not necessarily to match outdoor air purity.
Indoor air often has lower quality than outdoor air, primarily due to indoor contaminants. People spend about 90% of their time indoors, making good air quality essential. It is scientifically proven that the quality of air inside buildings is sometimes lower than the quality of air outside.
In fact, that is most often the case especially in homes and office buildings. The worse condition of the air inside buildings often comes from contaminants within that building, and may result to sickness for people who live, work or frequent these buildings.
Main Causes of Poor Indoor Air Quality
Indoor air contamination typically results from a combination of source pollutants and poor ventilation.
1. Inadequate Ventilation
Modern buildings are tightly sealed for energy efficiency.
Without sufficient air exchange:
• Contaminants accumulate
• Carbon dioxide levels rise
• Humidity increases
Ventilation systems must supply adequate fresh air to dilute indoor pollutants.
If fresh air intake is limited, pollutants concentrate.
2. Biological Contaminants
These include:
• Mold spores
• Dust mites
• Pet dander
• Pollen
• Bacteria
High humidity above 60% supports biological growth.
Basements, bathrooms, and poorly ventilated attics are common hotspots.
3. Volatile Organic Compounds (VOCs)
VOCs are gases released from:
• Paint
• Cleaning products
• Furniture
• Flooring adhesives
• Air fresheners
New renovations often increase indoor VOC levels temporarily.
Poor ventilation prolongs exposure.
4. Combustion Byproducts
Gas stoves, fireplaces, and furnaces can produce:
• Carbon monoxide
• Nitrogen dioxide
• Fine particulate matter
Improperly vented appliances significantly reduce air quality.
5. Building Materials and Furnishings
Off-gassing from:
• Pressed wood products
• Insulation
• Carpets
• Upholstery
Can release chemical compounds into indoor air.
Older buildings may also contain asbestos or legacy materials contributing to contamination.
Common Symptoms Of Poor Air Quality
People exposed to poor air quality indoors do not display fast, acute symptoms. These symptoms are subtle and slow. Normally, the symptoms are different for everyone and other stressors or problems such as heat may make them worse. Some people may not notice them while others may be more sensitive.
It is easy to view people affected by poor air quality as complainers or over-emotional since they symptoms are subjective. To take a more effective problem-solving approach, it is essential to place this issue on a scientific basis. Here are some of the common symptoms people affected by this problem might experience:
• General hypersensitivity reactions
• Irritation of throat, eyes and nose
• Nausea and even dizziness
• Dry skin and mucus membrane
• Wheezing and hoarseness
• Rashes and flushing or reddening of the skin
• Cough and airway infections
Sleepiness, headaches and general mental fatigue
How Indoor Air Quality Is Diagnosed
Diagnosing air quality problems begins with ventilation assessment.
Key checks include:
• Fresh air intake function
• HVAC filter condition
• Relative humidity levels
• Carbon dioxide concentration
• Visible mold presence
• Signs of water damage
Indoor humidity should remain between 35% and 50%.
CO2 levels above 1000 ppm often indicate inadequate ventilation.
Professional air quality testing may include:
• Air sampling
• Surface testing
• VOC monitoring
• Particle counts
Testing provides measurable data instead of assumptions.
Indoor Air Quality and Cognitive Performance
Air quality does more than affect breathing.
Emerging research links elevated carbon dioxide and particulate matter levels to reduced cognitive function.
In poorly ventilated offices:
• Decision-making accuracy drops
• Concentration decreases
• Reaction times slow
Even moderate increases in indoor CO2 can impair mental clarity.
This expands indoor air quality beyond comfort.
It becomes a productivity issue.
For remote workers and students, clean air directly supports performance.
This introduces new search relevance:
• Indoor air quality and brain fog
• CO2 levels and productivity
• Office ventilation and cognitive function
Indoor air affects both physical health and mental output.
How to Improve Indoor Air Quality
Improvement focuses on source control, ventilation, and filtration.
Improve Ventilation
• Open windows when weather permits
• Install HRV or ERV systems
• Ensure bathroom and kitchen fans vent outside
Control Humidity
• Maintain 35 to 50 percent relative humidity
• Use dehumidifiers in basements
• Fix leaks promptly
Upgrade Filtration
• Replace HVAC filters every 2 to 3 months
• Use higher MERV-rated filters where system allows
• Consider portable HEPA air purifiers
Reduce Pollutant Sources
• Choose low-VOC products
• Avoid synthetic air fresheners
• Store chemicals in sealed containers
• Clean dust regularly
Improvement does not require matching outdoor purity.
The goal is preventing health effects and maintaining safe exposure levels.
Why Indoor Air Often Becomes Worse Than Outdoor Air
Outdoor air benefits from natural dilution and dispersion.
Indoor air remains confined.
Pollutants accumulate in enclosed spaces.
Without proper air exchange, concentrations rise.
Energy-efficient construction reduces air leakage.
While beneficial for heating costs, it can trap contaminants inside.
Balanced ventilation is critical.
Determine If Your Building Has Poor Air Quality
You can call in the air quality testing experts to establish if enough air is getting into the building. Scientists recommend that office spaces have at least 5 cubic feet per minute per individual, of outdoor air. There exist similar recommendations for homes and other buildings.
Examine the behavior of people who reside in the building, and be alert to complaints of the common symptoms of poor air quality. Enhancing indoor air quality does not mean you have to make the air pristine and pure as that of the outdoor environment. However, it has to be relatively pure such that occupants do not experience any of the symptoms or illness caused by poor air quality inside their buildings.
The Mold Guy offer air quality testing and mold removal , to help you create a healthier home environment.
FAQs
How can indoor plants improve air quality?
Indoor plants can absorb pollutants and produce oxygen, enhancing air quality.
Are air purifiers effective in improving indoor air quality?
Air purifiers can significantly reduce airborne contaminants, improving indoor air.
What are the best practices for maintaining HVAC systems to ensure good indoor air quality?
Regular cleaning and filter changes in HVAC systems prevent pollutant buildup.
How does humidity affect indoor air quality?
Optimal humidity levels (30-50%) reduce mold growth and airborne pollutants.
Can opening windows improve indoor air quality effectively?
Opening windows allows fresh air in, diluting indoor pollutants and improving air quality.
Sources
Health Canada – Indoor Air Quality in Your Home
https://www.canada.ca/en/health-canada/services/air-quality/indoor-air-contaminants.html
Health Canada – Residential Indoor Air Quality Guidelines
https://www.canada.ca/en/health-canada/services/publications/healthy-living/residential-indoor-air-quality-guidelines.html
Government of Canada – Carbon Monoxide Safety
https://www.canada.ca/en/health-canada/services/air-quality/carbon-monoxide.html
Public Health Agency of Canada – Mould and Health
https://www.canada.ca/en/public-health/services/publications/healthy-living/mould-health.html
Canadian Centre for Occupational Health and Safety – Indoor Air Quality
https://www.ccohs.ca/oshanswers/indoor_air/iaq_general.html
