How CO2 Affects Your Brain
The idea that indoor CO2 impairs thinking is not speculation — it is backed by a growing body of peer-reviewed research. The most influential study came from Harvard University in 2015, and subsequent work has reinforced its findings across different settings and populations.
The Harvard COGFX Study
Researchers led by Joseph Allen at the Harvard T.H. Chan School of Public Health conducted the landmark COGfx (Cognitive Function) study. Knowledge workers performed standardised cognitive tests in controlled office environments at three CO2 levels:
- 550 ppm — baseline (well-ventilated)
- 945 ppm — typical office
- 1,400 ppm — poorly ventilated
Results were striking. Compared to 550 ppm, cognitive scores at 945 ppm dropped by 15 percent, and at 1,400 ppm by a remarkable 50 percent. The hardest-hit domains were crisis response, strategy, and information usage — precisely the skills knowledge workers need most.
Supporting Research
- Satish et al. (2012) found decision-making performance declined by 11-23 percent at 1,000 ppm versus 600 ppm, with even greater declines at 2,500 ppm.
- Fisk et al. (2013) estimated that improving ventilation in US offices could generate $20 billion in annual productivity gains.
- Wargocki et al. (2020) demonstrated that student performance in schools improved significantly when classroom CO2 was kept below 1,000 ppm — see our schools guide.
Why Does CO2 Impair Cognition?
The mechanisms are still being studied, but two pathways are well supported:
- Direct neurological effect — CO2 crosses the blood-brain barrier and may affect neurotransmitter function at elevated concentrations.
- Reduced oxygen displacement — very high CO2 can slightly reduce blood oxygen saturation, though this is more relevant above 5,000 ppm.
What You Can Do
- Monitor your workspace — a CO2 reading above 1,000 ppm is your signal to ventilate. See our office air quality guide.
- Target below 800 ppm — this is the sweet spot identified in our PPM guide.
- Ventilate proactively — do not wait for stuffiness. Use the CO2 calculator to set ventilation schedules.
- Track trends — reading your CO2 data over time reveals patterns you can act on.