A primary cause of cough is the common viral upper respiratory tract infection. It can cause acute cough and in this case, the cold viruses often cause a postnasal drip that causes a cough. This is considered as the most common cause of cough. Here, the cough is usually secondary to stimulation of nasal, pharyngeal, and laryngeal mucosa receptors. This mainly results from the secretions of the nose and sinuses draining into the throat. The viral illnesses may also be followed by a dry cough that may last up to several weeks.
A variety of underlying diseases are identified as the potential causes of chronic cough. The diseases like asthma, cystic fibrosis, allergies, GERD and chronic post nasal drip are considered the main causes of cough. Smoking is also considered a major cause of chronic cough. Croup is a disease of infants and young children, where harsh coughing and hoarseness and fever and difficult breathing is common. Croup is mainly characterised by a barking, "seal-like" cough and is caused by a virus. Another cause of cough is the disease Pneumonia. This is an infection that may be caused by viruses or bacteria. Apart from this, asthma is also considered as a cause of cough. This may be triggered by viruses, excessive exercise or an allergic trigger like dust, smoke, mold or pets.
Another cause of cough is the foreign body aspiration. This can cause cough if there is a history of a coughing or choking episode with eating, especially with small hard foods like nuts or popcorn. Sinusitis may be a cause of cough, as well. It usually causes cough at night or in the mornings. Among babies aged below one year, "spitting up" or gastroesophageal reflux may become a cause of cough. Here, cough is mainly caused because of small amounts of aspiration of food into the lungs. Its indications include cough after eating, cough when laying flat (for example, when going to bed), and cough when waking up in the morning. Sometimes, wheezing or recurrent Pneumonia may be associated with reflux.
Apart from the above mentioned causes, certain medications like angiotensin converting enzyme inhibitors (ACE inhibitors), used for hypertension are also considered as causes of cough. The ACE inhibitors are also used to treat high blood pressure or heart failure and they can cause coughing as a side effect. Most of the times, the cough caused by these drugs develops many months after the starting of their usage. Heartburn is another possible cause of cough. In this case, acid from the stomach may back up one's throat. This is commonly called as "acid reflux" and can cause heartburn or cough. Acid reflux is more common when a person is lying down. Cancer can also be considered as a possible cause of cough.
All the above mentioned factors are considered as most common causes of cough. However, there can be some other causes of cough that may also trigger more severe diseases.