What Harvard’s indoor air quality researchers found about the brain

If you care about your health, you’ve probably put real thought into what you eat and how you move. And if you care about health in the modern sense, you’re likely tracking a few metrics on top of that—sleep quality, VO2 max, protein intake, Zone 2 training.

There’s a variable most of that advice ignores: the room where all of it is happening.

Poor air quality linked to slower cognitive function

A series of studies out of Harvard’s T.H. Chan School of Public Health, known as the COGfx Study, spent years examining what indoor air quality actually does to cognitive function. The first study found that cognitive scores doubled when participants worked in better-ventilated spaces compared to conventional building environments—with the largest gains in areas like strategic thinking, information processing, and crisis response.

A follow-up study extended that research across 302 office workers in six countries. Same finding: as indoor CO2 and fine particulate matter increased, cognitive performance declined. For every 500ppm rise in CO2, response times slowed and mental throughput dropped measurably.

The researchers also found no lower threshold—even buildings operating within standard air quality guidelines showed cognitive improvements when ventilation increased.

Here’s what makes this interesting

The culprit isn’t usually outdoor pollution or anything you’d recognize as a problem. It’s CO2—what we exhale—quietly accumulating in any room that doesn’t get enough fresh air. Odorless and invisible, it doesn’t register as something worth addressing.

Which means the mental sluggishness you’ve been attributing to a bad night’s sleep, or a heavy week, may partly reflect the air quality of the room where you’re trying to think.

We spend roughly 90% of our time indoors. The air quality of your home office or bedroom is a condition your brain is working inside of every day.

What you can do

The gap doesn’t require a massive lifestyle change.

Opening a window for 5–10 minutes in the rooms where you sleep and work can meaningfully lower CO2, and the effect is immediate.

Candles, incense, and synthetic fragrances contribute to indoor particulate matter—one of the two main factors the research flagged—so if those are a regular part of your environment, they’re worth accounting for.

A higher-quality HVAC filter reduces PM2.5 passively; a small air purifier in your most-used room does the same without a central air system.

The bigger picture

Wellness culture spends a lot of time talking about what goes into (or happens inside) the body. But your environment also shapes that biology, and optimizing your inputs within a suboptimal space may only go so far.