In addition to being cramped and generally uncomfortable, airplane cabins oscillate between mildly chilly and absolutely frigid. On long flights, you’re typically afforded little respite between the thumping turbulence and the screaming child running down the aisle, and the temperature is usually sure to make you crave some kind of piping-hot tranquilizer.
But why are passenger plane cabins so cold? Business Insider reports on a 2008 study by the American Society for Testing and Materials, which probed the links between cabin pressure and fainting. The study ultimately found that a warm cabin contributes to the likelihood of passing out mid-flight.
The chances of fainting are augmented when you’re in an airplane, the study found, due to a condition known as hypoxia, which happens when you experience a “lack of sufficient oxygen in the blood, tissues, and/or cells to maintain normal physiological function,” according to the FAA. Hypoxia is pretty common, and can occur when flying in a “non-pressurized aircraft above 10,000 ft without supplemental oxygen.” It’s also stimulated during “rapid decompression during flight,” or a “pressurization system malfunction, or oxygen system malfunction.”