Acute bronchitis is the temporary inflammation of the bronchial tubes, the main airways leading into your lungs. This inflammation causes swelling and mucus production, resulting in a persistent cough, often called a chest cold. Although many people associate cold weather with getting sick, cold air itself does not directly cause bronchitis. The condition is fundamentally an infection or an irritation of the airway lining, and cold air acts only as a contributing factor or a trigger for symptoms.
The Pathogens That Cause Bronchitis
The actual cause of acute bronchitis is almost always an infectious agent, not the temperature of the air you breathe. The vast majority of cases, estimated to be between 85% and 95% in healthy adults, are caused by viruses. These are often the same common viruses responsible for the common cold or influenza, such as rhinovirus, adenovirus, and parainfluenza virus.
Viral particles are transmitted when someone coughs or sneezes, infecting the cells lining the bronchial tubes. The body’s immune response to fighting this infection leads to the inflammation and subsequent symptoms of coughing and mucus production. This viral nature explains why antibiotics are generally ineffective for treating acute bronchitis.
Bacteria are a far less frequent cause, accounting for only a small percentage of cases. Bacterial infections, such as those caused by Mycoplasma pneumoniae or Bordetella pertussis (whooping cough), are sometimes involved. They are more often secondary infections that occur after the immune system has been weakened by a primary viral illness. Viral transmission increases during colder months because people spend more time indoors in close proximity.
How Cold Air Triggers Airway Irritation
While cold air does not transmit the infectious agent, it can significantly aggravate the respiratory system. The air during winter is typically cold and dry, and this lack of moisture is a major irritant to the bronchial lining. As the body works to warm and humidify the air, it strips moisture from the mucous membranes in the airways, making them vulnerable.
This drying effect can cause irritation and inflammation, worsening an existing cough or making the airways more susceptible to circulating viruses. Sudden exposure to cold temperatures can also initiate bronchospasm, an involuntary constriction. This causes the muscles around the bronchial tubes to tighten and narrow.
Bronchospasm leads to wheezing and coughing, symptoms that mimic or intensify those of acute bronchitis. Cold exposure can also temporarily suppress the local immune defenses in the respiratory tract. This reduction makes it easier for an existing or incoming virus to take hold and cause a full-blown infection.