The space where many individuals spend approximately a third of their life might also be harming them, as highlighted by sleep and air-quality specialists. In 2015, a study in Scotland examined airtight, naturally ventilated homes over a winter period. Over 80% of these homes showcased CO2 levels beyond safe limits throughout the night. Surprisingly, more than 90% of the occupants were unaware of the issue, believing their bedroom air quality was acceptable.

By 2026, experts indicate that this issue is emerging as a summer risk due to heatwaves challenging homes lacking proper infrastructure, amidst rising global temperatures. Biomedical engineer Devjoy Dev explains, “Global warming causes drastic and abrupt shifts in temperatures.” This situation leads to severe heatwaves in regions like Europe, where air conditioning infrastructure is often limited. Additionally, bedroom fabrics such as curtains and carpets exacerbate the problem by trapping heat and moisture at night.

Dr. Ayesha Bryant, a clinical adviser at Alpas Wellness in Maryland, noted a study revealing average nighttime carbon dioxide levels in bedrooms exceeding 1,520 parts per million (ppm). Elevated CO2 levels serve as indicators of stale air. These levels, measured in parts per million, demonstrate how confined CO2 and heat can impair sleep quality long before individuals notice something amiss.

So, with high temperatures persisting overnight in confined rooms, what are the long-term health effects?

A Room With No Thermostat

The issue isn’t the room itself but rather what changes when its occupant falls asleep. During wakefulness, individuals naturally adjust their environment—opening windows if the air feels stale or closing them if cold. This self-regulation ceases during sleep, leading to built-up CO2 and moisture. Bryant mentioned that while CO2 isn’t perilous at these levels, it signifies poor air exchange, associated with reduced sleep quality and impaired performance the following day.

A 2022 study involving 40 Danish bedrooms concluded that cognitive function declined when CO2 levels reached 1,800 ppm, with sleep quality being affected before reaching this point, resulting in various health problems over time.

“Keep in mind the sleep environment and its ‘zeitgebers,'” said Dev, referring to external cues such as light and temperature that affect the body’s circadian rhythm. Regulating these factors is crucial for achieving restorative sleep as elevated CO2 and moisture levels disrupt them.

Clearing the Air

Inadequate airflow, closed doors, weak insulation, and west-facing windows trap heat in bedrooms. A June study by Amerisleep found that 52% of Americans consider themselves hot sleepers, with 94% waking weekly because of it, as opposed to 58% of cold sleepers. Women were twice as likely as men to wake three or more times a week due to heat. While the preferred bedroom temperature is 65–67°F, the common actual temperature tends to be 68–70°F.

Bryant advises keeping trickle vents clear and ventilating rooms when outdoor conditions allow. “Lüften,” a German practice now popular with young generations, involves airing rooms by fully opening windows for 10 to 15 minutes each morning to eliminate stale, humid air. Dehumidifiers, priced between £90 and £300, can maintain humidity levels around the ideal 60%. For consistently hot rooms, fixing HVAC systems or incorporating air conditioning is recommended, and any mold or condensation issues should be addressed at the root rather than only cleaning the surface.