There are various possible causes, such as inhalation of harmful or toxic atmospheric pollutants, fine particulate matter (PM2.5), which can stimulate the cough receptors in the airways, and inflammatory mediators secreted by some inflammatory cells in the airway mucosa during airway inflammation, which can also directly stimulate the cough receptors, resulting in a dry cough. The external ear canal, nasal mucosa, throat mucosa, pleura and pericardium all have cough receptors and lesions in these areas can also produce a dry cough.