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 2016 study by Strøm-Tejsen et al. published in Indoor Air compared sleep at roughly 1,150 ppm vs 2,400 ppm CO2. The lower-CO2 condition was associated with better-reported sleep quality and better next-day cognitive performance.

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

These are general guidelines synthesized from indoor-air-quality and sleep research; specific thresholds vary by study and individual.

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. Bedroom CO2 studies show that even slightly open windows can substantially reduce overnight CO2 levels. 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. Once Komori ships, your overnight CO2 trend will be plotted alongside 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.