Post nasal drip does NOT cause acid reflux 

More Info: Individuals who suffer from acid reflux at times simultaneously experience symptoms of post-nasal drip, leading them to conclude that either one causes the other. But there is little evidence to show that post-nasal drip causes acid reflux. The reverse however is true: acid reflux can cause post-nasal drip.

Post Nasal Drip Caused by Acid Reflux

Post-nasal discharge or PND is caused by either swallowing disorders, excessive or thick mucous accumulation in the throat and throat muscle disorders . When any of these conditions occur, they result in a sensation that mucous is dripping from the back of the nose, which is why it is also known as post-nasal drip.

One of the causes of swallowing disorders in particular is gastroesophageal reflux disease, better known as acid reflux disease. This condition is characterized by the backwards movement or reflux of the contents of the stomach or small intestine into the esophagus . The root cause of acid reflux is the weakening or loosening of the lower esophageal sphincter, the muscle band which closes off the stomach . The substances that reflux into the esophagus include acid, pepsin and bile. They not only cause heartburn, regurgitation, vomiting and nausea; but can cause ulcers, damage in the esophagus and even esophageal cancer.

Acid reflux can also affect swallowing because the acid and other stomach contents accumulate in the throat as it moves up from the esophagus . Acid reflux can also cause or aggravate asthma or sinusitis, which in turn result in post-nasal drip .

Laryngopharyngeal Reflux and Post-Nasal Drip

Another condition very similar to gastroesophageal reflux disease or acid reflux creates the sensation of post-nasal drip in the throat. This condition is called laryngopharyngeal reflux (LPR).  Laryngopharyngeal reflux or LPR refers to the chronic symptoms or mucosal changes, such as postnasal drip sensation and sore throat, which are caused by the regurgitation of the gastric contents into the laryngopharynx . Unlike acid reflux however, the patient does not experience the symptoms of heartburn and nausea .