A cough that's continued for more than three weeks may be a sign of allergies, asthma or chronic bronchitis, according to Dr Henry Milgrom, an allergist at the American National Jewish Medical and Research Center in Denver.

Many people let a persistent cough go untreated for too long. If a cough doesn't go away, you should see a doctor to learn if it is symptomatic of something more serious and treatable, Milgrom says in a prepared statement.

The three stages of the cough
He explains that coughs are defined in three stages: acute, sub-acute and chronic.

An acute cough lasts less than three weeks and, if you feel fine otherwise, usually doesn't require a visit to your doctor.

However, if fever, discomfort or generalised malaise accompanies your cough or if your cough is keeping you awake at night, by all means see a doctor, Milgrom says.

A cough that persists for more than three weeks may be an indication of something more serious. A sub-acute cough, lasting three to eight weeks, may be a sign of sinusitis, viral or bacterial infection, allergies or mild asthma.

A symptom of many conditions
A chronic cough, lasting longer than six weeks, may be a symptom of gastroesophageal reflux, chronic bronchitis, undiagnosed asthma or chronic obstructive pulmonary disease (COPD).

Chronic bronchitis and COPD are frequently accompanied by mucus, whereas some other illnesses associated with chronic cough are not, Milgrom says. - (HealthDayNews)

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