Have you ever been on an airplane, minding your own business, and found your eyes filled with tears for no reason? Or perhaps you sat near someone who burst into tears. Is there something happening to your body that triggers (引发) the tears?

There sure is! When you're inside a flying airplane, you're miles off the ground. Not exactly a place where humans usually find themselves. The airplane is pressurized (加压) to keep passengers comfortable. But it's still not the pressure levels that you'll experience at ground level. It's a bit like having climbed a pretty high mountain.

The primary tear-trigger is the lower amount of oxygen in your blood. The oxygen levels in the plane are lower than you'll find on the ground. And it can bring you bad feelings.

Another cause is dehydration(脱水). Because the air in the plane is very dry, we may get dehydrated. And being dehydrated can have all kinds of harmful effects on your 30,000-foot-high body, which is making you have bad feelings like sadness and worry. In fact, there is a spiritual reason, too! Even if you're not afraid of planes, it's a high-stress situation. Taking a flight often involves saying goodbye to someone in the place you're leaving. You can also be worried about plane crash or losing your baggage.

You can drink plenty of water before your flight to fight back your tears. You can also keep your mind busy with a puzzle or brain game. And if you're going to watch a movie, maybe choose one that's a bit more relaxing. In short, make flying a more pleasant and less stressful experience.