The reflex of coughing is initiated chemical and mechanical irritation of laryngeal and tracheobronchial receptors.1
Chemical receptors are sensitive to acid, heat, and capsaicin-like compounds via activation of the type-1 capsaicin receptor.
Additionally, there are multiple neural sensory receptors located within the external auditory canals, eardrums, paranasal sinuses, pharynx, diaphragm, pleura, pericardium, and stomach which are all capable of stimulating the coughing reflex. These are mechanical receptors that stimulate secondary to triggers such as touch or stretch.