If you check your sleep score every morning the way other people check the weather, you may already suspect that a stuffy bedroom shows up in the data. Specific, measurable changes in bedroom air are tied to specific, measurable changes in sleep architecture, and a run of studies between 2023 and 2026 now show what those changes look like: less deep sleep, more arousals, worse next-day performance.

What Happens to Deep Sleep When Bedroom CO2 Rises?

A 2023 study published in Buildings put people through a night of sleep at three CO2 levels simulating one, two, and three occupants in a bedroom: 680, 920, and 1,350 ppm. Sleep was tracked with polysomnography, which is an overnight diagnostic test that measures brain activity, eye movements, heart rhythm, breathing, blood oxygen levels, and limb movements.

The deep sleep proportion dropped from 20.4% at 680 ppm to 17.3% at 920 ppm to 14.4% at 1,350 ppm — roughly a 30% reduction in deep sleep between the lowest and highest levels of CO2 tested. The arousal index (a metric that measures the number of times per hour your brain briefly wakes up or shifts to a lighter mode of sleep) climbed alongside it, and body movements during the night increased by about 50%. Subjects also self-reported worse sleep quietness and more throat and nasal irritation at the higher concentrations of CO2.

For context: 1,350 ppm isn't an extreme number that’s hard to achieve. It's what a closed bedroom door and a couple of sleepers can produce by 3 a.m. without ventilation.

Does Particulate Matter (PM2.5) Change Your Sleep Architecture?

A separate field study of 163 university students, published in Scientific Reports, measured actual bedroom particulate matter levels overnight and matched them against sleep staging and next-day physical performance. PM2.5 was significantly associated with a reduction in the proportion of deep sleep, and the effect showed up even at a median exposure of just 25.5 µg/m³, well below what most people would consider a “bad air quality day.”

The same study found CO2 and PM2.5 compounding each other: at elevated CO2 (around 3,961 ppm) alongside higher particulate levels, the hit to next-day performance worsened. Temperature mattered too; deep sleep proportion increased within a 61–79°F range, while humidity's clearest effect showed up in next-day physical performance, with an inverted-U pattern peaking around 60% relative humidity.

Why Does Deep Sleep Matter This Much?

Deep sleep is the stage where tissue regenerates and the body releases the hormones tied to physical recovery. It's also when breathing, heart rate, and blood pressure all drop to their lowest points of the night.

It's the stage most sleep-tracking algorithms weight heavily in a nightly “readiness” or recovery score. And most people are breathing bedroom air for a large share of their lives to begin with: Americans spend about 90% of their time indoors, on average.

Is This Why Your Wearable's Sleep Score Dips on Stuffy Nights?

Possibly. Consumer sleep trackers estimate the same architecture these studies measured directly with polysomnography — time in deep sleep, arousals, movement — using heart rate, HRV, and motion as proxies. They're not lab-grade, but they're measuring the same underlying phenomenon, which is why a night in a closed, unventilated room can produce a lower deep-sleep percentage or a worse “readiness” score without any obvious explanation the next morning.

It also means air quality is one of the few sleep variables that's both cheap to monitor and mechanically simple to fix. You can't will your way to more deep sleep, but you can open a window, and the CO2 study above suggests that alone accounts for a meaningful share of the swing.

Practical Ways to Improve Your Home Air Quality

The research points to a short, practical list:

• Track CO2, not just temperature. A basic CO2 monitor will tell you when a closed bedroom is creeping past 1,000 ppm. Cracking a window or door is often enough to bring it back down.
• Keep the room in the 61–79°F range. Both studies found temperature swings outside a moderate band worked against deep sleep.
• Don't ignore particulate sources. Candles, unfiltered HVAC, wildfire smoke infiltration, and even cooking odors drifting from the kitchen can push bedroom PM2.5 up without any obvious smell.
• Ventilate before you optimize everything else. Both studies point to airflow as the single lever that moves CO2 and PM2.5 downwards. 

What About Overnight Pathogen Exposure?

CO2, particulates, temperature, and humidity are one axis of bedroom air quality. Airborne and surface pathogens are a different axis, and especially relevant for anyone sharing a bed or a house with kids, a partner, or roommates who occasionally bring something home from school or the office. Getting sick is its own, more obvious way a night's sleep gets disrupted.

That's the axis Beacon operates on. Beacon is an EPA-registered Far-UVC disinfection device that uses 222nm light to continuously inactivate up to 99.99% of pathogens in the air and on surfaces, including the ones that cause influenza, RSV, COVID-19. It runs quietly in the background all night, with no fan noise or filter-change routine competing for your attention the way a CO2 monitor or a ventilation fix might.

Beacon doesn't change your bedroom's CO2 or particulate levels; for those, ventilation and filtration are still the tools that matter, per the research above. What it does is handle the pathogen side of the air continuously, without adding another thing to your nightly checklist.