Why airplane cabins are kept cold

"The sweet spot for a plane’s cabin temperature is somewhere between 21 and 24 Celsius degrees," Bobby Laurie, a former flight attendant and co-host of the travel and lifestyle talk show, The Jet Set, tells Popular Science.

This is the indoor temperature at which most people feel comfortable. However, because airplane cabins have lower humidity (of 10-20% to prevent airframe corrosion, drier than most deserts), passengers can feel much colder.

On commercial airplanes, the cabin's simulated air pressure remains at an altitude equivalent of 1,800 to 2,400 meters above sea level to protect the plane's structural integrity. While most passengers don't notice this shift, their bodies are actually exposed to 25% less oxygen than they would get at sea level.

This sudden drop in oxygen can make feel dizzy or lightheaded or even faint, particularly during overnight flights. To prevent this, flight crews intentionally use the cold air to keep passengers more alert, especially in case of sudden turbulence or evacuations.

Warm temperatures make it harder for the body to maintain circulation; the heart beats faster and pumps blood harder, thereby requiring more oxygen.

Conversely, cold air slows the heart rate, keeps breathing steady, and stabilizes blood oxygen levels. It also reduces nausea and motion sickness by calming the body's temperature regulation system.

Keeping the cabin cold also helps regulate the body's moisture. Normally, the low humidity in a cabin accelerates the evaporation of moisture from human skin, causing sudden dehydration. However, cooler air slows down this process, thus making the enclosed space feel much less stuffy during long flights.

Cool cabin temperatures provide several advantages for passengers. Photo by Pixabay

According to Rosen Aviation, a freezing cabin is a shield against illness as well. Because germs and bacteria thrive in warm environments, keeping the cabin cold limits their spread. Besides, low humidity, combined with the aircraft’s air conditioning system, also helps eliminate airborne microorganisms.

Aircraft systems operate more efficiently in cold conditions. Cool air helps onboard electronics dissipate heat, contributing to better system efficiency and longevity.

All commercial aircraft are equipped with a built-in environmental control system that manages cabin pressure, temperature, and air quality. The ECS distributes conditioned air to several distinct zones throughout the aircraft.

The passenger cabin is typically divided into two to four independent temperature-control zones (e.g., forward, mid, and aft sections). To manage the temperature in each specific area, the aircraft utilizes trim air valves, which inject small amounts of hot or cold air into the main airflow ducts, allowing for localized temperature adjustments.

Some aircraft are capable of adjusting the cabin environment in real time, thanks to thermal imaging technology and monitoring systems. This technology can automatically detect spots prone to temperature fluctuation and make quick adjustments to keep the entire cabin consistently cool.