How CO2 Levels in Your Bedroom Affect Your Sleep

You Might Be Sleeping in Bad Air

Here's something most people never think about: every night, you spend 7-9 hours in a closed room, breathing the same air. With every breath, you exhale CO2. In a poorly ventilated bedroom, CO2 levels can climb from a comfortable 400 ppm to over 2,500 ppm by morning.

That matters more than you think.

What the Science Says

A landmark 2015 study from the Technical University of Denmark found that participants who slept in rooms with lower CO2 levels (below 900 ppm) reported significantly better sleep quality, performed better on cognitive tests the next morning, and felt more refreshed upon waking.

The mechanism is straightforward: elevated CO2 doesn't just make the air feel "stuffy." It increases your breathing rate, elevates heart rate, and can trigger more frequent micro-arousals throughout the night. You don't wake up fully — but your sleep architecture is disrupted.

What "Good" Air Looks Like

CO2 Level	Quality	Effect on Sleep
Below 600 ppm	Excellent	Optimal sleep conditions
600-1000 ppm	Good	Minimal impact
1000-1500 ppm	Fair	Noticeable reduction in sleep quality
Above 1500 ppm	Poor	Significant disruption, morning grogginess

Most bedrooms with closed windows and doors will exceed 1,500 ppm by midnight. With two people in the room, it happens even faster.

Simple Fixes

The easiest intervention is opening a window — even a crack. Studies show that even slightly open windows reduce average overnight CO2 by 50%. If outdoor noise or temperature makes that impractical, a simple HEPA air purifier with fresh air intake can help. CO2 is just one piece of the puzzle — for a complete walkthrough, see our guide on setting up your bedroom for better sleep.

Why We Built CO2 Monitoring Into Komori

Most sleep trackers ignore air quality entirely. They track your body but not your environment. When we designed Komori, we included a CO2 sensor because the data consistently shows that where you sleep matters as much as how you sleep. Your overnight CO2 trend is plotted alongside your sleep data, so you can see the correlation for yourself.

You might be optimizing everything else — your mattress, your temperature, your routine — while the air itself is the problem. If you're serious about improving your rest, explore how Komori helps you get better sleep by tracking both your body and your environment.