Drainage from the nose has almost as many causes as the ways that people describe it. The terms runny nose, excess mucous, and postnasal drainage all refer to disorders that cause patients to be bothered by excess nasal drainage. There are three general conditions that contribute to most of these issues: Allergic rhinitis, Nonallergic rhinitis, and Vasomotor rhinitis.
Allergic rhinitis, as its name implies, is caused by underlying allergies. Symptoms may include nasal drainage, postnasal drainage, and congestion. If left untreated, Allergic rhinitis can also lead to chronic sinusitis; blockage of the sinuses contributes to facial pressure, facial pain, headaches, and infection.
Nonallergic rhinitis, in many ways, mimics Allergic rhinitis, except that the allergy cells normally seen in the mucous of patients with Allergic rhinitis are absent. Irritants, such as those from occupational exposure, strong fumes, smoke, perfumes, etc., can cause a nonallergic reaction that manifests as nasal drainage.
Vasomotor rhinitis is a disorder resulting from an over-active nerve in the nose, specifically the posterior nasal nerve. This increased activity is often associated with eating, leading patients to complain of excess nasal drainage during and after meals.