Causes of foamy saliva include obstructions or infections of the oropharynx or the esophagus, according to a published report on the National Center for Biotechnology Information. Water brash or gastroesophageal reflux disease, nasogastric intubation and idopathic achalasia are some of the possible esophageal obstruction or infections.
Ptyalism or sialorrhea refers to a condition of saliva overflow, according to the report on NCBI. Drugs like lithium, nitrazepam and clozapine can change normal saliva flow, causing excessive saliva flow. Apart from disorders of the esophagus and oropharynx, heavy metal poisoning, menstrual cycle's secretory phase and various kinds of neurological disorders can also induce saliva overflow. Obstructions in esophagus can be due to cancer, stricture formation or any kind of foreign body.