Indoor Air Quality and Cognitive Performance: Everything You Need to Know

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Written By Jamila W.

Americans spend over 90% of their time indoors. This means that we’re spending the majority of our time breathing indoor air which the Environmental Protection Agency says is up to four times dirtier than outdoor air. Indoor air quality has a significant impact on our health, with prolonged exposure to polluted, stagnant, or recirculated air even affecting our thinking processes. In this article, we’ll explore everything you need to know about indoor air quality and cognitive performance, including the factors that affect air quality, the effects of poor air quality on cognitive function, and effective strategies for improving indoor air quality to optimize your cognitive performance.

Indoor Air Quality and Cognitive Performance

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We’re all familiar with experiencing symptoms like headaches, fatigue, and difficulty concentrating in a room that is muggy, musty, or has strong chemical odors. But an increasing number of research studies using cognitive tests have established a significant association between indoor air pollution and cognitive impairment. Indoor air quality is now a public health issue, with a global burden that affects developed and developing countries, with a wide range of air pollutants deteriorating:

  • Cognition
  • Brain health
  • Mental focus 
  • Mental acuity
  • Computation
  • Cognitive throughput
  • Short-term and long-term memory

Studies have demonstrated and characterized a sobering causal relationship between indoor air quality and cognitive performance, with increases in fine particulate matter and carbon dioxide concentrations increasing cognitive impairment. Public health organizations like the World Health Organization attribute a variety of health problems including cognitive decline and poor mental health to cumulative and transitory exposures to polluted indoor air.

What is Indoor Air Quality?

The Environmental Protection Agency defines Indoor Air Quality (IAQ) as the air quality within 

and around buildings and structures, particularly in relation to the health and comfort of building occupants. Air quality comprises the levels of a range of air constituents and pollutants that can impact human health. Raised levels of airborne substances like carbon dioxide, smoke, vapors, mold, and chemicals deteriorate IAQ, with indoor air pollutant exposure linked to various symptoms and health conditions, including cognitive performance.

Understanding Indoor Air Quality

Poor air quality inside buildings and structures has negative effects on cognitive performance, and wider health, especially if building occupants are exposed to the air for a prolonged period or are susceptible to health effects due to pre-existing health conditions. By understanding the factors that affect indoor air quality, you can take steps to improve indoor air quality and promote better cognitive performance and overall health.

Factors Affecting Indoor Air Quality

Understanding the factors that affect indoor air quality is critical for understanding the mechanisms by which cognitive performance is impaired and for maintaining a healthy environment. The factors that can affect indoor air quality include:


Indoor air quality is degraded by a wide range of pollutants that are suspended in indoor air. Building occupants are exposed to them through inhalation. They span substances produced by the building occupants, microorganisms, particulates, and organic and inorganic chemicals:

Type of indoor air pollutants



Smoke, soot, PM10, PM2.5, PM1 particles


Bacteria, viruses, mold spores, 


Pollen, dust mites

Organic (carbon-containing) gasses

Carbon dioxide, carbon monoxide, 

Volatile organic compounds (VOCs)

Formaldehyde, benzene, toluene, xylene

Inorganic glasses

Nitrogen dioxide, sulfur dioxide, ozone

Radioactive gasses 



Ventilation is critical for the control of indoor air pollution as it brings in outdoor air that dilutes existing air pollutants and prevents their buildup in indoor spaces. Mechanical and passive ventilation also generates air movement, makes breathing more comfortable, and lessens the risk of health problems. 


High humidity levels have a potentiating effect on indoor air pollution. The high levels of water vapor create stagnancy that prolongs the suspension of particulate pollutants in the air. High humidity also promotes the growth of mold and other harmful organisms.


Raised temperatures also contribute to a muggy indoor environment that is uncomfortable for occupants. In the absence of active or cross-ventilation, exposure to harmful airborne contaminants is increased.

Outdoor Air Quality

Outdoor air quality has a significant effect on indoor air quality, with buildings located near sources of outdoor air pollution typically having lower indoor air quality. Pollutants like ozone, sulfur dioxide, nitrogen dioxide, and PM2.5 particulates move inside buildings with outdoor air. Once inside a building, the pollutant levels can become up to 100 times higher than outdoor air pollution levels if ventilation is poor.

The Impact of Indoor Air Quality on Cognitive Performance

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Cognitive skills or performance relates to the broad brain-based skills we develop for essential thinking activities and processes like

  • Skill or knowledge acquisition
  • Reasoning
  • Recalling information
  • Evaluation of information
  • Decision-making

Cognition spans neurological areas that include perception, attention, language, and memory. It is essential to be able to function at any level of society and complete the common activities of daily living. So anything that impacts short-term and long-term brain health not only impacts cognition but also the ability of affected individuals to function normally. 

Indoor air quality is part of the wider area of indoor environmental quality (IEQ) that includes lighting, thermal environment, layout, and acoustics. Both IAQ and IEQ are increasingly recognized as affecting the cognitive function of building occupants, especially as people are spending increasing amounts of time learning or working from home.  

Poor indoor air quality degrades cognitive performance, with a universal decline in a wide range of different cognitive tasks. This is important because, in advanced economies, work and learning are predominantly cognitive rather than physical. 

Studies and Research Demonstrating the Impact of Indoor Air Quality 

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Research on the impact of indoor air quality on cognitive performance has been conducted for several years. Numerous studies have shown that poor indoor air quality can have a negative impact on cognitive performance in standardized tests like the digit symbol substitution test. Here is a round-up of notable research studies that have shown the effect of poor indoor air quality on cognition:

A 2012 study undertaken by Upstate Medical University, State University of New York, and Lawrence Berkeley National Laboratory demonstrated an association between raised indoor carbon dioxide levels and impaired decision-making and work performance in office workers. In addition, the higher carbon dioxide (CO2) concentrations were associated with the perception of poorer air quality.

The UN Environment Program cited research carried out in 2018 between Yale University and the University in Beijing, China that showed that cumulative exposure to fine particulate matter, sulfur dioxide, and nitrogen dioxide impeded performance in verbal and math tests. There was a distinct gender difference in research findings with male older adults being the most affected, particularly in verbal scores.

A 2020 project undertaken by Lawrence Berkeley National Laboratory to improve HVAC system ventilation in California K1-12 schools found that improving indoor air quality can improve cognitive function by up to 10%. The study found that only 15% of classrooms were receiving the median daily ventilation rate, and elevated carbon dioxide levels of over 2,000 parts per for much of the school day.

In 2021, Harvard University conducted a study involving a cohort of 300 office workers in various countries. The study found that the workers who have a well-ventilated office environment with low levels of PM2.5 air pollution scored significantly higher on neuropsychological tests than those who work in poorly ventilated offices with high levels of ambient air pollution. Poor indoor air quality was found to reduce cognitive function by as much as 50% (as measured by test scores). 

A 2022 French population-based cohort study with over 61,000 participants published in The Lancet found that air pollution exposure to fine particulate matter, black carbon, and nitrogen dioxide was associated with a statistically significant decrease in cognitive abilities of up to 5%. The study found that executive function, the mental skills associated with working memory and flexible thinking, were particularly affected in subjects in the study population.

Other studies have also demonstrated a relationship between indoor exposure to air pollution and 

  • Physical symptoms such as headaches, fatigue
  • Cardiovascular diseases
  • Difficulty concentrating
  • Socioeconomic status
  • Respiratory problems, which further impact cognitive performance. 
  • Increased school and workplace absences 
  • Employee concerns about their workplace environmental quality
  • Erroneous moves made by chess tournament players 
  • Impaired cognitive development and primary school attainment in childhood
  • Lower cognitive function in childhood and adolescence
  • Cognitive dysfunction and dementia in older adults along with confirmatory neuroimaging and biomarkers

These diverse studies suggest that by improving indoor air quality cognitive functioning outcomes can be improved, with increased productivity, and better overall health.

Proposed Mechanisms for Indoor Air Quality Affecting Cognition

The mechanisms behind the effect of air pollution on health and cognitive functioning are not yet fully understood, but there are several theories that have been proposed by scientists and clinicians to better explain this adverse relationship.  

Carbon dioxide accumulation

Poorly ventilated environments often have raised concentrations of carbon dioxide. This gas acts as a sedative with neurological and respiratory depression, via medullary (brainstem) receptors that lead to drowsiness and difficulty concentrating. Extremely high levels of carbon dioxide in indoor air have a narcotic effect and environmental exposure is capable of reducing consciousness. 

Poor sleep quality 

The impact of indoor air pollution on sleep has also been suggested as the reason why it causes cognitive impairment. Elevated levels of particulates and allergens can cause irritation and inflammation of the upper respiratory tract, which induces or exacerbates sleep problems like snoring and obstructive sleep apnea. The partial obstruction of swollen airways also increases blood carbon dioxide concentration as minute ventilation is affected. The drowsiness that follows impacts cognitive performance.

Physical symptoms

Poor indoor air quality can also lead to physical symptoms such as headaches, fatigue, and respiratory problems. These short-term effects of indoor air pollution make it difficult for affected individuals to concentrate or process information while they are experiencing discomfort. The poorer cognitive performance is alleviated by providing good air quality.

Inflammation in the brain 

A notable theory is that exposure to indoor air pollutants can cause inflammation in the brain, which can lead to cognitive impairment seen in conditions like dementia and Alzheimer’s disease in older-aged adults. Inhaled air pollutants can travel directly to the brain via the olfactory bulb (nerve endings in the nose related to smell) where it can cause inflammation, oxidative stress, and cytotoxicity with DNA damage.

Interference with neurotransmitters

Air pollution in indoor environments can also interfere with the transmission of neurotransmitters, which are essential for cognitive function. This effect is thought to be particularly marked in infants, children, and adolescents. 

Improving Indoor Air Quality

There is substantial evidence that improving indoor air quality creates a healthy and productive environment where cognitive performance improves and age-related cognitive decline is arrested. This makes it vital that this modifiable risk factor for dementia is addressed with urgency. Here are some ways to improve your indoor air quality and reduce the impact of air pollution on cognitive performance in your household:

Use an Air Purifier 

Air purification is one of the most effective ways to rid indoor spaces of airborne contaminants for easier breathing and enhanced cognitive performance. The great thing about running an air purifier is that the uplift in air quality is immediate as the device traps, absorbs, or destroys common allergens and air contaminants. These appliances can be installed in any indoor space and use a range of technologies to remove harmful pollutants from the air including:

  • HEPA filtration
  • Activated carbon filtration
  • Photoelectric catalytic oxidation
  • Ultraviolet germicidal irradiation (UVGI) 
  • Ionization

The different types of air purifier vary in their efficacy against pollutants including fine and ultrafine particulates, organic and inorganic glasses, and biological materials. The improvement in air quality reduces ongoing exposure to pollutants, protecting building occupants from their harmful respiratory and inflammatory effects on an ongoing basis. 

Increase Ventilation

Improving passive and mechanical ventilation is one of the most effective ways to prevent the buildup of pollutants in an indoor environment. Proper ventilation continuously removes stale air and brings in fresh air from outside to replace it. You can boost cross-ventilation by opening windows and doors and using extraction fans in the kitchen and bathroom. Properties can be upgraded with the installation of a whole-house ventilation system that delivers continuous fresh air to your home while removing stale air to prevent the buildup of air pollution in room air.

Control Humidity

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High humidity also contributes to poor indoor air quality. It is a common problem that can be caused by structural defects in a property, or human activities like cooking, showering, or drying clothes. You can reduce humidity in your property by increasing ventilation when showering, covering saucepans when cooking, and using a clothes dryer that is vented outside.  You can also run a dehumidifier, an appliance that actively traps and condenses water vapor in room air to reduce mold and mildew.x

Other steps

Air quality can also be improved by addressing the activities that generate indoor air pollutants like tobacco smoke, VOCs, and particulates. Avoiding smoking indoors, selecting cooking methods and fuel sources that do not generate particulates, and seeking alternatives to 

Harsh chemicals and fragrances are all sustainable steps for improving IAQ. Maintaining a clean and clutter-free living space also reduces the accumulation of dust and other allergens.

Role of Building Design in Indoor Air Quality

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Building design plays a crucial role in ensuring that the air inside your building is healthy and safe to breathe. The phenomenon of sick building syndrome has shown that building infrastructure can be a massive reservoir of toxic pollutants that are gradually released into indoor air. Two important aspects of building design can have a significant impact on indoor air quality: sustainable building materials and design for ventilation. Some examples of sustainable building materials include:

  • Bamboo flooring
  • Recycled glass countertops
  • Sheep’s wool insulation
  • Low-VOC paints and finishes

By using sustainable building materials, you can reduce the number of harmful pollutants that are released into the air inside your building and lessen the cognitive impact of air pollution exposure.

Designing for Ventilation

Another important aspect of building design that can impact indoor air quality is ventilation. Proper ventilation promotes the removal of pollutants and other harmful particles from the air inside your building and needs to be integrated into the building’s design. When designing a building, it’s important to consider the ventilation system and ensure that it meets the needs of the occupants. Some key factors to consider when designing for ventilation include:

  • The number of occupants in the building
  • The type of activities that will take place inside the building
  • The location of the building (e.g., near a busy road or industrial area)

By designing for ventilation, you can help to ensure that the air inside your building is healthy and safe to breathe, reducing the impact of air pollution on cognitive function.

Indoor Air Quality and Cognitive Performance:  Frequently Asked Questions

How does indoor air quality affect cognitive function?

Indoor air quality can have a significant impact on cognitive function. Poor air quality can lead to symptoms such as headaches, fatigue, and difficulty concentrating, which can negatively affect your ability to perform mental tasks. Exposure to pollutants such as volatile organic compounds (VOCs) and particulate matter can also have long-term effects on cognitive function during an individual’s life course including the acceleration of dementia and the development of Alzheimer’s disease.

What are the effects of high CO2 concentrations on cognitive performance?

High concentrations of carbon dioxide (CO2) can hurt cognitive performance. When CO2 levels are too high, it can cause drowsiness, headaches, and difficulty concentrating. This can lead to decreased productivity and poor performance on cognitive tests.

Can carbon dioxide hurt blood vessels?

Research has shown that high levels of carbon dioxide also cause constriction of blood vessels in the brain, reducing blood flow and oxygen delivery. This causes symptoms such as dizziness, headaches, difficulty concentrating, as well as poorer cognitive outcomes.

Is there a link between air quality and productivity?

Yes, there is a link between air quality and productivity. The economic costs of exposure to air pollution are increasingly recognized by economists and the business sector. According to the Clean Air Fund, the decrease in the productivity of office workers on high-pollution days cost firms more than $24 billion in 2019. Indoor air pollution can lead to symptoms such as fatigue, headaches, and difficulty concentrating, which can negatively affect your ability to perform mental tasks. On the other hand, good air quality can help improve focus and productivity.

What are some basic strategies to improve indoor air quality?

Some basic strategies to improve indoor air quality include:

  • Ventilate your space by opening windows and using exhaust fans
  • Use air purifiers to filter out pollutants
  • Avoid smoking indoors
  • Use natural cleaning products
  • Control humidity levels to prevent mold growth

What are the main parameters assessed in a general indoor air quality assessment?

A general indoor air quality assessment typically includes measurements of temperature, humidity, carbon dioxide levels, particulate matter, and VOCs. These measurements can help identify potential sources of polluted air and guide strategies to improve air quality.

What are healthy buildings?

Healthy buildings’ is a new concept that takes a holistic approach to the design, construction, and ongoing maintenance of buildings, keeping the health, well-being, and productivity of office workers and other occupants as a priority. Because people spend the majority of their time indoors, healthy buildings need to provide optimal indoor environmental quality, particularly managing indoor air quality with strategies like competent ventilation and control of indoor air pollutants, dust, and pests. 

In Conclusion

In conclusion, the quality of the air you breathe indoors can have a significant impact on your cognitive performance. Indoor air pollution can lead to symptoms such as headaches, fatigue, and difficulty concentrating, which can ultimately affect your productivity and overall well-being.

It’s also important to note that certain factors, such as smoking and the presence of mold or asbestos, can significantly impact indoor air quality and pose serious health risks. If you suspect that your indoor air quality is compromised, you may need professional help to identify and address any underlying issues.

By taking these steps to improve your indoor air quality, you can promote better cognitive performance and overall health.