The Cough Reflex
Coughing is a complex protective reflex which is the normal means of cleansing the bronchi, the airway tubes to the lungs, of excessive fluids or unwanted matter. It is associated with other protective processes such as mucus secretion and narrowing of these tubes. Coughs are usually initiated by a irritation in the bronchi. However, coughs can also result from irritation in the ear canal or to the pleural membrane around the lungs. Causes of coughing include inhaled irritants, inflammation, infections, fibrosis, blood clots, tumors, or lung congestion from heart insufficiency. Infections are by far the most common cause of acute coughs.

In the absence of a coughing, material is normally expelled from the respiratory tract by the action of small hairs on the inner surface of the respiratory tubes which continually move the coating of mucus at rates of up to one centimeter per minute. This mucus coating is an important defense mechanism, since it collects and moves waste matter and inhaled particles away from the lungs. Respiratory fluids are normally produced by small glands and goblet cells in the bronchi. These fluids prevent irritation of the cells lining the respiratory airways.

A number of factors can interfere with the function of the airway lining and produce the need for coughing. Inflammation from irritants or infection can increase respiratory fluid production and the number of immune defense cells, and leading to excessive sputum production. The number of goblet cells in the bronchial membrane increases in chronic bronchitis or after chronic exposure to mild irritants. In people exposed to tobacco smoke or other inhaled irritants the movement of the small hairs is reduced, mucus production increases, lung cleansing is diminished, and the airways narrow. Viral infections can interfere with the motion of the small hairs and make the respiratory fluid thicker.

Reducing exposure to irritants, especially by stopping smoking, is an important means to avoid arousing the cough reflex. Adequate hydration is essential to avoid drying of the membranes. Simple steam inhalation can be adequate for reducing coughs due to irritation of the respiratory airway below the throat. For infections a number of different types of remedies can be of benefit.

Dry and Productive Coughs
Most acute infections of the respiratory tract are viral and recovery can be rapid and spontaneous. The coughs of viral infections are at first dry and spasmodic, but small amounts of white, thick sputum are usually produced as they progress. This type of cough can either be relieved with cough suppressants or made productive by using expectorants. Acute dry coughs may also be due to inhaled irritants or from a blood clot passing into the lungs. Chronic dry coughs are noninfective, usually due to either fibrosis or congestive heart failure which needs to be specifically treated.