Typically a cough is worked-up depending on how long it has lasted. A cough is considered acute if it lasts less than three weeks. These coughs are usually caused by short-term infections (i.e. upper respiratory infections), most often the common cold caused by a run-of-the-mill virus. Coughs lasting between 3 and 8 weeks are termed subacute, and have a broader range of causes. Subacute coughs may be caused by persistent infections (such as with whooping cough, or pertussis) or post-nasal drip (often accompanied by the sensation of always having to clear one's throat). Asthma
and gastro-esophageal reflux can also present with persistent coughing. Coughs lasting beyond 8 weeks are considered chronic; causes typically include reflux, asthma, persistent infections, and other types of lung disease. Any cough lasting 8 weeks or longer should be worked up with a chest x-ray
regardless of smoking status. If the chest x-ray is not revealing, a trial of bronchodilators for asthma and a trial of antacids for reflux disease should be undertaken. If concern for asthma is high enough, formal pulmonary function testing
should be done. Certain medications (classically a type of blood pressure medications called ACE inhibitors) can also produce cough, and a time relationship between the cough and new medication use should be examined.