Why Do I Get So Dehydrated When I Fly?

Airplane flying over a desert
Photo: iStockphoto

Dry throat and itchy eyes—we’ve all felt the effects of flying. According to Dr. Clayton T. Cowl, the chair of Preventive, Occupational, and Aerospace Medicine at the Mayo Clinic, an aircraft’s filtration system—which takes in outside air and circulates it in the cabin—is to blame. While this creates a clean environment, it also causes humidity to drop to a parched 10 to 20 percent—between 30 and 65 percent is comfortable for most people. Low humidity means that moisture evaporates from the body quickly, which can lead to dehydration. Plus, when air is dry, the throat’s broomlike cilia become less effective at sweeping out viruses and bacteria, so you may be more susceptible to illness.

The final word: There are ways to combat low humidity besides drinking water. Avoid alcohol- based moisturizers, which can be drying (Cowl recommends a vitamin E lotion); pack natural eyedrops and saline nasal spray; and skip the wine and cocktails.

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