Coughs are usually classified according to their duration:

1. Acute coughs usually last less than three weeks and have a sudden onset, perhaps caused by an upper respiratory tract infection such as a cold or sinusitis; an infection of an area further down the airways (as is the case in pneumonia and bronchitis); inhalation of dust, smoke or another foreign substance; an allergy such as hayfever, or a flare-up of a long-term respiratory condition, such as asthma or chronic obstructive pulmonary disease (COPD).

2. Subacute coughs are usually of around three to eight weeks duration. Infections are the usual cause, particularly whooping cough (pertussis) in children.

3. Chronic cough sufferers are less likely to be able to put a finger on what has caused their cough, as it usually has a more gradual onset. Examples include a longer-term allergy (e.g. to house dust mites); an undiagnosed respiratory condition such as chronic bronchitis or asthma, or a side effect of smoking or medication, particularly ACE inhibitors. Postnasal drip €“ mucus dripping from the nose into the throat because of a condition such as sinusitis €“ is another possible cause, as is irritation of the throat by leaking stomach acid as a consequence of gastro-oesophageal reflux disease (GORD). Persistent coughs can also be a sign of something more serious (e.g. lung cancer, tuberculosis, pulmonary embolism or heart failure), although this is rare.

Coughs can also be referred to as chesty or dry. A chesty or productive cough will often make the sufferer feel as if they are trying to bring something up €“ usually described as mucus or phlegm. On the other hand, a dry, tickly or non-productive cough often starts as a tickle at the back of the throat, which causes the person to cough.