According to 'The New York Times," people should not fly if they have pneumonia. Because of the pressure changes that occur during flight, ill people find traveling by air very uncomfortable or even painful.
CNN explains that pressure changes occur in large planes that are 30,000 to 40,000 feet in the air. Smaller planes that don't go above 10,000 feet do not have pressure problems. At the higher altitudes, when people have respiratory, sinus or ear conditions, the infected body cavities expand, and the increased pressure sometimes becomes excruciating.
CNN reports that people with other conditions should refrain from flying, as well. Those with serious communicable diseases should not board planes. In addition, anyone recovering from abdominal, eye, ear or face surgery, dental work or a concussion should stay grounded.