This is generally due to hypoxia, a medical condition that occurs when the body tissue does not receive enough oxygen ? and it can happen a lot more than you think in plane passengers. Another thing that can trigger hypoxia is an overheated cabin, so that's why temperatures are kept below average.

Airplanes are kept cold primarily for a medical reason known as hypoxia-related fainting. High cabin pressure combined with warm temperatures can trigger passengers to faint more easily because the body struggles to regulate its internal temperature when oxygen levels are slightly lower than at sea level. By keeping the cabin air "crisp" (typically between 71°F and 75°F), airlines significantly reduce the risk of medical emergencies. Furthermore, with hundreds of people packed into a confined space, body heat and electronics can cause the temperature to spike rapidly. In 2026, newer aircraft have more granular climate controls, but flight attendants still tend to err on the side of "chilly," as it is much easier for a passenger to put on a sweater than it is to cool down a passenger who is on the verge of heat-induced syncope.