While a cough once in a while is common, a cough that lasts for several weeks or one that brings up discolored or bloody mucus may be a sign of a medical condition. A cough is called "acute" if it lasts less than three weeks. It's called "chronic" if it lasts longer than eight weeks in adults or longer than four weeks in children.

Infections or flares of chronic lung conditions cause most acute coughs. Most chronic coughs are related to underlying lung, heart or sinus conditions.

Common infectious causes of acute cough

Common infectious causes of acute cough include:

1. Acute sinusitis
2. Bronchiolitis (especially in young children)
3. Bronchitis
4. Common cold
5. Croup (especially in young children)
6. Influenza (flu)
7. Laryngitis
8. Pneumonia
9. Respiratory syncytial virus (RSV)
10. Whooping cough

Some infections, particularly whooping cough, may cause so much inflammation that the cough can last for many weeks or even months after the infection itself has cleared up.

Common lung causes of chronic cough

Common lung causes of chronic cough include:

1. Asthma (most common in children)
2. Bronchiectasis, which leads to a buildup of mucus that can be streaked with blood and raise the risk of infection
3. Chronic bronchitis
4. COPD — a long-term lung disease that causes trouble with breathing.
5. Cystic fibrosis
6. Emphysema — a lung condition that causes shortness of breath.
7. Lung cancer
8. Pulmonary embolism
9. Sarcoidosis
10. Tuberculosis

Other causes of cough

Other causes of cough include:

1. Allergies — Injury, such as from a blunt trauma or burn.
2. Choking: First aid (especially in children)
3. Chronic sinusitis
4. Gastroesophageal reflux disease (GERD)
5. Heart failure — a condition in which the heart doesn't pump blood as well as it should.
6. Inhaling an irritant, such as smoke, dust, chemicals or a foreign body
7. Medicines called angiotensin-converting enzyme inhibitors, also known as ACE inhibitors
8. Neuromuscular diseases that weaken the coordination of upper airway and swallowing muscles
9. Postnasal drip, which means fluid from the nose runs down the back of the throat