Classification
A cough can be classified by its duration, character, quality, and timing. The duration can be either acute (of sudden onset) if it is present less than three weeks, subacute if it is present between three and eight weeks, and chronic when lasting longer than eight weeks. A cough can be non-productive (dry) or productive (when sputum is coughed up). It may occur only at night (then called nocturnal cough), during both night and day, or just during the day.
A number of characteristic coughs exist. While these have not been found to be diagnostically useful in adults, they are of use in children. A barky cough is part of the common presentation of croup, while a staccato cough has been classically described with chlamydia pneumonia.
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