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Signs and symptoms
PND is classically described as the sensation of something "dripping down the throat" and may also present with rhinorrhea, constant throat clearing, and cough, although its symptoms can be very nonspecific. It is one of the most common etiologies for chronic cough, defined as a cough persisting beyond 8 weeks.

Causes
There are multiple causes of PND, which can be acute or chronic.

Allergic rhinitis
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 obstruction. The increased rhinorrhea and mucus production can result in PND.

Non-allergic rhinitis
Non-allergic rhinitis (NAR) is a condition with symptoms of rhinitis, including rhinorrhea and nasal obstruction, with negative skin and serum allergy testing results. It can be further categorized into:


 * Non-allergic rhinitis with eosinophilia (NARES)
 * Hormonal rhinitis (such as during pregnancy)
 * Medication-induced rhinitis
 * Atrophic rhinitis
 * Irritant and occupational rhinitis (including tobacco smoke, cleaning supplies, etc.)
 * Idiopathic nonallergic rhinitis

Rhinosinusitis
Rhinosinusitis is inflammation or infection of the sinus cavities. Acute rhinosinusitis has symptoms lasting less than four weeks, while chronic rhinosinusitis lasts greater than 12 weeks. This persistent irritation can also lead to increased mucus production as a result of pro-inflammatory pathways, producing symptoms of PND.

Mechanism
The exact mechanism of PND depends on its etiology, but usually involves increased production of mucus from the nasal mucosa. In addition to providing sense of smell, the nasal cavity serves to filtrates and regulates the temperature and humidity of inspired air. The nasal mucosa can produce secretions, or mucus, that provides lubrication and protection for the nasal cavity. This mucus production is activated by the autonomic nervous system; specifically, cholinergic neuropeptides are responsible for increasing mucus production. 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.

Diagnosis
Diagnosis of PND depends on both a detailed history and clinical examination to help determine its etiology. The history may begin with feelings of obstructed nasal breathing or "stuffy nose" with or without nasal discharge. If allergic rhinitis is suspected, a family history of allergic conditions as well as a personal history of other associated conditions such as food allergy, asthma, and atopic dermatitis can be evaluated. Allergic rhinitis classically has more symptoms of sneezing attacks, itchy eyes, and respiratory problems, although it is difficult to distinguish the different types of rhinitis by symptomology alone. - find symptoms specific to PND - Visual inspection can reveal mouth breathing, which is suggestive of nasal obstruction.

Treatment
In one meta-analysis, intranasal steroids were shown to improve symptoms of non-allergic rhinitis at four weeks better than a placebo.

Epidemiology
Because PND is often characterized as a "symptom" rather than a separate condition, the exact incidence is unknown and varies by its etiology. Chronic rhinitis, which includes allergic and non-allergic rhinitis, can affect 30-40% of the population. Non-allergic rhinitis is more common in females.