Cough - Causes of a cough

Most coughs are caused by viral infections and usually clear up on their own.

Doctors often classify coughs according to how long they last. For example, a cough is classed as:

• acute - if it lasts for less than three weeks
• subacute - if it lasts for 3-8 weeks
• chronic (persistent) - if it lasts for more than eight weeks

Short-term cough (acute)

Most people with a cough have a respiratory tract infection caused by a virus. This includes:

• upper respiratory tract infections (URTIs), which affect the throat, windpipe or sinuses - such as the common cold, influenza (flu), laryngitis, sinusitis or whooping cough
• lower respiratory tract infections (LRTIs), which affect your lungs or lower airways - such as acute bronchitis and pneumonia (although this is rare)

Possible non-infectious causes of an acute cough include:

• allergic rhinitis, such as hay fever
• a flare-up of a chronic condition such as asthma, chronic obstructive pulmonary disease (COPD) or chronic bronchitis  

In rare cases it may be the first sign of a health condition causing a chronic (long-term) cough (see below).

Long-term cough (chronic)

A persistent cough in adults may be caused by:

• a long-term respiratory tract infection
• a long-term condition, such as asthma
• allergies
• smoking - smoker's cough can also be a symptom of chronic obstructive pulmonary disease (COPD)
• postnasal drip (mucus dripping down the throat from the back of the nose, caused by a condition such as rhinitis)
• gastro-oesophageal reflux disease (GORD) - due to irritation and damage caused by stomach acid
• a prescribed medicine, such as an angiotensin-converting enzyme inhibitor (ACE inhibitor), that's used to treat high blood pressure (hypertension) or cardiovascular disease

Rarely, a cough is a symptom of a more serious condition such as lung cancer, heart failure, a pulmonary embolism (clot on the lung), cystic fibrosis or tuberculosis (TB).