Post-nasal drip (PND), also known as upper airway cough syndrome (UACS), occurs when excessive mucus is produced by the nasal mucosa.

However, some researchers argue that the flow of mucus down the back of the throat from the nasal cavity is a normal physiologic process that occurs in all healthy individuals.

Gastroesophageal reflux disease (GERD) is often associated with a high prevalence of upper-respiratory symptoms similar to those of PND, such as coughing, throat clearing, hoarseness and change in voice.

[2] Allergic rhinitis (AR) is a common condition where exposure to allergens results in the release of inflammatory mediators, such as histamine, that causes sneezing, rhinorrhea, itchy eyes, and nasal congestion.

[7] Excess mucus can drain posteriorly into the upper and lower airways, which, along with other physical and chemical irritants, can activate receptors in the respiratory tract that results in a protective physiological cough.

[10][7] Visual inspection can reveal mouth breathing, which is suggestive of nasal obstruction, or a horizontal crease across the nose (caused by the "allergic salute").

As such, suggestive procedures that highlight rhinitis and mucopurulent secretions, such as nasoendoscopy, may instead be utilized because of the vague nature of information available to directly attribute specific symptoms to the syndrome.

[7] Azelastine, a topical antihistamine, is approved for both allergic and non-allergic rhinitis due to its unique anti-inflammatory effects separate from its histamine receptor antagonism.

[14] Other methods, such as drinking warm fluids and using saline nasal irrigation, may be useful for managing symptoms of PND but their exact efficacy is unclear in medical literature.