An occasional cough is normal — it helps clear foreign substances and secretions from your lungs and prevents infection. But a cough that persists for weeks is usually the result of an underlying problem. In many cases, more than one cause is involved.

Major causes

  • Postnasal drip. When your nose or sinuses produce extra mucus, it can drip down the back of your throat and trigger your cough reflex. This condition is also called upper airway cough syndrome.
  • Asthma. An asthma-related cough may come and go with the seasons, appear after an upper respiratory tract infection, or become worse when you're exposed to cold air or certain chemicals or fragrances. In one type of asthma (cough-variant asthma), a cough is the main symptom.
  • Gastroesophageal reflux disease (GERD). In this common condition, stomach acid flows back into the tube that connects your stomach and throat (esophagus). The constant irritation can lead to chronic coughing. The coughing, in turn, worsens GERD — a vicious cycle.

Studies have shown that the above three causes, alone or in combination, are responsible for 90 percent of cases of chronic coughs.

Other causes

  • Infections. A cough can linger long after most symptoms of a cold, influenza, pneumonia or other infection of the upper respiratory tract have gone away. A not uncommon cause of a chronic cough in adults is pertussis, also known as whooping cough.
  • Blood pressure drugs. Angiotensin-converting enzyme (ACE) inhibitors, which are commonly prescribed for high blood pressure and heart failure, are known to cause chronic cough in some people.
  • Chronic bronchitis. This long-standing inflammation of your major airways (bronchial tubes) can cause congestion, breathlessness, wheezing and a cough that brings up discolored sputum. Most people with chronic bronchitis are current or former smokers.

Less common

  • Aspiration
  • Bronchiectasis
  • Bronchiolitis
  • Chronic bronchitis from an infectious disease
  • COPD
  • Cystic fibrosis
  • Foreign body aspiration — children
  • Laryngopharyngeal reflux
  • Lung cancer
  • Nonasthmatic eosinophilic bronchitis
  • Sarcoidosis
May. 24, 2013