Cough, Mucus - Causes

A cough can be a protective action. When there are foreign particles in your air passages, special nerve endings will signal your body to cough so you that these particles do not go into your airways. However, a cough that lasts for a couple of weeks or a cough that expels out blood or abnormally colored phlegm may be a symptom of an underlying medical problem.

A cough can be classified based on how long it lasts:

- An acute cough lasts for 3 weeks or less.  Common causes of an acute cough include the common cold, flu, and pneumonia.
- A subacute cough lasts 3 to 8 weeks. Common causes of a subacute cough include bacterial infection of the sinus.
- A chronic cough lasts more than 8 weeks. Common causes of a chronic cough include smoking, asthma, and gastroesophageal reflux disease (when acid from your stomach goes back up towards your throat).

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