A cough is a sudden expulsion of air from the lungs. Its purpose is usually to clear secretions and inhaled foreign substances from the lungs and respiratory tract.

There are different types of cough:

  • Acute cough—lasts for less than three weeks
  • Subacute cough—lasts 3-8 weeks
  • Chronic cough—lasts longer than eight weeks

An acute cough is usually caused by an infection, such as a cold or flu. In some cases, an acute cough can be the sign of other conditions, such as:

  • Exposure to an irritant or an allergen
  • Aspiration of a foreign body
  • Acute bronchitis
  • Pneumonia

Subacute cough is often a cough that follows a respiratory infection. It can also be caused by exposure to irritants or to anything that can cause chronic cough.

A chronic cough has many causes. Common examples include:

Alveoli (Air Sacs) of Lung
Chronic Bronchitis
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