The feeling of drowsiness in a crowded, stuffy room is a common experience, but it points to a significant environmental issue with direct effects on brain function. Elevated indoor concentrations of carbon dioxide (CO2), a gas produced by our own respiration, can impair cognitive abilities. This problem concerns the quality of the air inside buildings where people spend the majority of their time. As structures become more energy-efficient and airtight, the risk of CO2 buildup increases, diminishing mental performance in offices, schools, and homes.
The Physiological Impact of CO2 on the Brain
When a person inhales air with elevated carbon dioxide levels, the concentration of CO2 in the bloodstream rises, a condition known as hypercapnia. The primary response within the brain is vasodilation, the widening of blood vessels to increase blood flow and deliver more oxygen to brain tissue. Although this response increases blood moving through the brain, it can alter brain chemistry and reduce the efficient use of oxygen by neurons. The increased blood CO2 level can lead to respiratory acidosis, where the blood’s pH becomes more acidic, interfering with cellular processes and neurotransmitter functions.
The body’s reaction to higher CO2 is an automatic, protective measure, but this response is what appears to trigger cognitive deficits. The feeling of sleepiness or mental fog that occurs in a poorly ventilated room is a direct symptom of these physiological changes. As CO2 accumulates, the brain’s oxygen regulation is disrupted, impacting the neural activities that underpin clear thought.
Measurable Effects on Cognitive Performance
The physiological changes from increased CO2 inhalation translate into quantifiable declines in cognitive abilities. Scientific research has demonstrated a direct link between CO2 concentrations and performance on specific mental tasks. Studies from the Harvard T.H. Chan School of Public Health simulated office environments with varying air quality to measure the impact on workers, revealing significant drops in higher-order thinking skills as CO2 levels rise.
In one study, participants’ cognitive scores were, on average, 15% lower at CO2 levels of 950 parts per million (ppm) and dropped by 50% at 1,400 ppm. The most affected areas were complex strategic thinking and crisis response. For instance, in simulated crisis scenarios, participants’ performance was 131% higher in well-ventilated, low-CO2 environments. Information usage, or the ability to effectively apply available data, was another area that saw a dramatic decline.
These effects are not limited to extreme scenarios and have been observed in typical indoor settings. A study from the University of Colorado Boulder projected that at indoor concentrations of 1,400 ppm, basic decision-making ability could be cut by 25%, and complex strategic thinking by around 50%. These findings make the abstract concept of cognitive impairment a concrete issue for productivity and learning.
CO2 Levels and Their Sources in Indoor Spaces
Carbon dioxide concentration is measured in parts per million (ppm). Outdoor air contains around 420 ppm of CO2, while indoor levels below 1,000 ppm are considered acceptable for maintaining good cognitive function. Research shows that cognitive impairment can begin to appear at levels around 1,000 ppm, with significant effects documented at 1,400 ppm and above.
The primary source of elevated CO2 in indoor spaces is human respiration. In enclosed or poorly ventilated spaces, this gas quickly accumulates. This issue is common in modern environments designed for energy efficiency, which often feature sealed windows and a reliance on recirculated air. Crowded classrooms, tightly sealed office buildings, and small meeting rooms are frequent sites of high CO2 buildup.
Strategies for Improving Indoor Air Quality
Improving indoor air quality to reduce cognitive impairment primarily involves enhancing ventilation. The most direct method is to increase the circulation of fresh outdoor air.
- Open windows and doors, even for short periods, to flush out stale, CO2-rich air and lower indoor concentrations. Creating cross-ventilation is particularly effective.
- Ensure that a building’s heating, ventilation, and air conditioning (HVAC) system is functioning properly. Adjusting HVAC systems to increase the intake of outdoor air can significantly reduce CO2 levels.
- Regularly replace air filters, which can become clogged and restrict airflow.
- Use fans to circulate air within a space to help prevent CO2 from becoming concentrated in one area.
- Use an indoor CO2 monitor to identify when levels are becoming elevated, prompting action to improve ventilation.
- Take regular breaks to go outside to breathe fresh air.
Standard air purifiers, such as those with HEPA filters, are designed to remove particulate matter and do not remove gaseous pollutants like CO2 from the air.