The prime objective of this article is to know about post nasal drip. Post nasal drip happens when excessive mucus is produced by the nasal mucosa. The excess mucus accumulates in the throat or back of the nose. It is caused by rhinitis, sinusitis, gastro esophageal reflux disease (GERD), or by a disorder of swallowing. It is often caused by an allergy, which may be seasonal or persistent throughout the year.