By Dr Patrick Chan

IT usually starts with a little tickle at the throat. The tickle increases in intensity, and before we know it, we are coughing away.

Everyone has experienced a serious bout of coughing at least once in their lives, and the experience is never pleasant especially if it happens in the midst of something important such as a meeting or a teleconference!

Still, coughing is an important physiologic defence mechanism. It is the body's natural way of protecting the respiratory system by clearing the airway of irritants or secretions.

A cough reflex happens spontaneously when an irritant stimulates the lining of the airway, resulting in a forceful release of air from the lungs to clear any possible blockages and expel any irritants.

A cough usually goes away after some time. Sometimes, however, it may become frequent and prolonged when the respiratory system is infected or continue to be inhaled by exposure to environmental pollutants such as vehicle fumes, smoke or haze.

Once this happens, it can have significant impact upon patients, as it disrupts sleep and appetite.

Chronic coughing can leave one too exhausted to go to school, work or function as normal.

Recognising certain types of cough may help you to decide when to seek medical help rather than waiting for it to go away by itself.

Types of cough

Coughs can be described as dry or productive. A dry cough does not produce mucus, while a productive cough sounds wet and may result in the expectoration of phlegm/mucous.

A dry, brassy cough may indicate an inflammation of the larynx, whereas coughing lots with a deep breath something like a whoop may be a sign of a respiratory tract infection caused by a pertussis.

A barking cough may be caused by a viral infection of the vocal cords, larynx and trachea.

If you are having productive cough, paying attention to the colour and appearance of the sputum can help you determine the type of infection you are having.

A purulent and brownish mucous suggests a bacterial infection, a white grey mucous indicates allergy or viral infections, whereas a pink frothy sputum is linked to pulmonary oedema (swelling).

Patients with heart failure usually have wrecking coughs during the night when lying down, whereas smokers and asthmatic patients usually have early morning, episodic cough that may be associated with wheeze.

In more serious conditions, the sputum may contain blood.

Frequent coughing that lasts fewer than two weeks can be classified as acute cough. This usually results from viral respiratory infection such as the common cold and flu.

A cough that lasts more than two weeks is considered a chronic cough.

Although a chronic cough is usually not life-threatening, it is important to investigate the underlying problems if the cough persists.

Causes of cough

The major causes of cough are respiratory infections such as:

1. Colds and flu - the most common cause of cough caused by viruses.

2. Whooping cough - contagious respiratory tract infection caused by a bacterium, Bordetella pertussis.

3. Bronchitis - an inflammation of the mucous membranes of the bronchial airways.

4. Pneumonia - an infection of the lung tissues.

5. Croup - a viral inflammation of the larynx, trachea and bronchial passage, mostly in young children.

6. Tuberculosis - a bacterial infection that causes blood-stained sputum and weight loss.

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