Bronchitis is the medical term for a chest cold. Viral infections are the most common cause of acute bronchitis. Dr. Alan Greene, pediatrician and Clinical Professor of Pediatrics at Stanford University, notes that research indicates cold air in and of itself does not cause colds or bronchitis. Although you must be exposed to an infective organism to get bronchitis, running in the cold can make you more likely to get sick once you have been exposed.
Acute bronchitis results from a viral or bacterial infection that causes the bronchial tubes to become inflamed. These tubes swell and produce excess mucous, which irritates the lungs and causes a cough. In addition to the cough, you may have a headache, body aches, a fever and sore throat. When you cough you may produce mucous that is yellow or green in color. Severe bronchitis may cause wheezing or shortness of breath.
Running and the Immune System
Strenuous exercise such as running can depress the immune system. A position statement published in the 2011 “Exercise Immunology Review” by the International Society of Exercise and Immunology notes that acute intense exercise can depress antibody production and production of T-cells. T-cells are one of the body's systems for fighting infection. White blood cells, another infection-fighting mechanism, increase immediately after strenuous exercise but then drop to low levels before they return to normal. When white blood cells are low, immunity to infection is lessened.
Exercise in Heat and Cold
Exercising in environmental extremes such as heat, cold or at high altitude may increase the body's stress response and promote the development of respiratory infections such as bronchitis. Research results reported in the December 2003 issue of “Aviation, Space and Environmental Medicine” said that exercising in conditions of extreme heat or cold produced disturbances in immunity. The high temperature environment was 100 degrees Fahrenheit with a relative humidity of 45 percent and the cold was 46 degrees, with a relative humidity of 50 percent.
Cold Air and Mucous
Dr. Greene says that cold air can affect the mucous transport system. Your respiratory system has a thin covering of mucous called the mucous blanket, which traps organisms like viruses and bacteria. Running in cold air increases mucous production but also makes it thicker, so it is more difficult to clear your mucous. Bacteria and viruses in the mucous stay in contact with your lungs longer and this may increase the risk of infection.
Nasal Congestion and Histamine
Breathing cold air through the nose can also increase nasal congestion and stuffiness, which makes it more difficult for the body to remove bacteria and viruses that have been inhaled, according to Dr. Greene. Cold air can also cause the release of a chemical called histamine, which can cause wheezing or exercised-induced asthma. The combination of all of these factors increases the risk of bronchitis if you run in cold air and are exposed to an infectious organism. Greene recommends that you breathe through your nose while running and drink plenty of fluids to help keep the mucous thin.