Temps must be low, usually below zero Fahrenheit. No tissue actually freezes, but severe bronchial irritation results from sucking down very cold air faster that the human airway can warm it up. The irritation produces spasms in the muscles of the airway and a burning pain, with the possibility of coughing up blood. Increased mucus production frequently creates wheezing sounds when the sufferer breathes. A severe case might last one to two weeks.
Treatment is rest, warm and humidified air to breathe, and plenty of water to drink.
A third worrisome phenomenon, which can appear with temperatures as high 60 degrees F, is chilblains. They aren't mentioned much in the United States, but approximately one in every ten residents of England have experienced these red, itchy skin lesions. When skin is kept cool and moist for a long time, rewarming causes a rush of blood to the heat-dilated vessels near the surface of a human body. The swollen vessels can't take the load. Fluid and metabolic waste products leak out of the vessels and into the surrounding tissue.