Colds, flu and allergies are common causes of post nasal drip, according to WebMD. Certain medications and foods also cause post nasal drip. Other potential causes include a deviated septum, pregnancy, hay fever and sinusitis, as stated by Healthline.
Dryness in heated homes and buildings causes thick secretions, explains the American Academy of Otolaryngology. Thick secretions from one nostril in children usually mean that something is stuck in the nose. Patients sometimes experiences nasal drip if they do not clear mucus away effectively, says WebMD. Swallowing problems cause a buildup of mucus in the throat, and this feels like nasal drip.