“During a flight, cabin humidity is often less than 10 per cent, while our skin typically feels comfortable with 50 per cent humidity,” explains Professor Michael Detman, co-founder and chief scientific office of Iräye, of why we often get puffy on flights.

Getting "puffy" after a flight—a condition often called "Jet Bloat"—is primarily caused by the drop in air pressure and the effects of prolonged immobility. When you are in a pressurized cabin at 35,000 feet, the pressure is lower than at sea level, which causes gases in your body to expand, leading to abdominal bloating and a "full" feeling in your face and limbs. Simultaneously, sitting still for hours in a cramped seat causes blood and fluids to pool in your lower extremities due to gravity and a lack of muscle contraction (which normally helps pump blood back to the heart). This is known as "peripheral edema." Dehydration also plays a significant role; the air in a plane is extremely dry (often less than 10% humidity), and when the body is dehydrated, it tends to "hold on" to any available water, causing fluid retention and puffiness. To minimize this, frequent flyers are encouraged to drink plenty of water, avoid salty "airplane snacks," and wear compression socks to encourage circulation. Getting up to walk the aisle every hour is the most effective way to prevent the fluid buildup that leads to swollen ankles and a puffy "post-flight" face.