This is due to drier mucous membranes:
Dehydration can be a real concern for air travelers, especially those with health problems. An airplane cabin at cruising altitude can be drier than the Sahara Desert, with relative humidity between 10 and 20 percent. “You’re actually more prone to infection because it dries mucous membranes,” said Dr. Marc Siegel, an internist and associate professor of medicine at New York University School of Medicine.
