<unk>  is the uncontrollable flow of saliva outside the mouth. It can occur in either some nervous system disorders or anatomic abnormalities of the oral cavity. Either the production of saliva is excessive, the musculature of the mouth which normally controls the oral opening, is weak and not functioning to the adequate strength to help keep the saliva inside or there is difficulty in swallowing.
Firstly we will discuss the production of saliva, which is carried out by the salivary glands. Upon receiving the excitatory stimulus from salivary nuclei present in the brain stem, saliva is produced, which occurs in response to the taste, and visual stimuli received from the tongue and other parts of the mouth. These are categorized into minor and major salivary glands. The major glands, which are most impressive are present in the base of the mouth, front of teeth, and in the cheeks, known as submandibular, parotid, and sublingual glands. So in total, there are 6 major glands that secrete saliva.
Isolated<unk>  is a common phenomenon in babies, often associated with teething, but it usually stops at around 15-36 months, when the baby develops salivary continence.<unk>  in infants and young children may be exacerbated by upper respiratory infections and nasal allergies. The persistence of Sialorrhea after 4 years of age is therefore considered pathologic at times. It may persist due to hyper-salivation, or neurologic disorders like cerebral palsy, Parkinson’s disease, and amyotrophic lateral sclerosis, or as a side effect of medications. The most common cause of sialorrhea in children is Cerebral palsy whereas, in adults, Parkinson's disease is the most common cause. Other contributing factors for<unk>  are dental malocclusion, postural issues, and an inability to recognize salivary spills.<unk>  associated with fever or trouble swallowing may be a sign of a more serious disease including:
Retropharyngeal abscess
Peritonsillar abscess
Tonsilitis
Mononucleosis
Strep throat
Parkinson's disease
Sudden onset<unk>  may be an indication of poisoning (predominantly by pesticides) or a reaction to snake or insect venom. It can also be a side effect of numbed mouth from either orajel use in the dentist's office or medications. Some neurological problems also cause<unk> . Excess intake of Capsaicin can lead to<unk>  as well, an example being the ingestion of particularly high Scoville Unit chili peppers.
Seasonal Allergies from pollen, trees, grass, mold, and weeds can also cause excessive saliva production and be a cause for<unk> . Another form of ptyalism is associated with pregnancy, most common in women with a condition known as Hyperemesis Gravidarium, or uncontrollable and frequent nausea and vomiting during pregnancy which is far worse than typical "morning sickness". With Hyperemesis, ptyalism is a side-effect, which is a natural response to uncontrollable vomiting. With normal vomiting, salivary glands are stimulated to lubricate the esophagus and mouth to aid in expelling stomach contents. During a hyperemesis pregnancy, many women complain of excessive saliva and an inability to swallow this saliva. Some women note-having to carry around a "spitoon" or using a cup to spit. Swallowing their own saliva has been noted to gag and further nauseate the women making the hyperemesis that much worse.
There are several theories as to the causes of hyperemesis and related symptoms such as ptyalism. Many physicians are reluctant to treat hyperemesis since they don't see it as a true physiological illness but rather "in the patient's mind" [note: this is an old fashioned view and the medical community now considers hyperemesis as a real and serious physiological condition]. Many pregnant women who suffer end up terminating the pregnancy. Others refuse to carry another child. The most frequent act is preparing for the onset of hyperemesis if a subsequent pregnancy is expected.<unk>  is very bothersome, and can lead to many complications, both physical and psychosocial. Maceration and infection of the skin around the mouth, halitosis, dehydration, abnormalities in speech, and feeding difficulties are some of the complications. Also,<unk>  increases the chances of aspiration of saliva, food, or fluids into the lungs, especially with deranged reflex mechanisms like gagging or coughing. Moreover, people suffering from this face psychosocial troubles like isolation, education difficulties,  increased level of dependency, decreased self-esteem, and difficult socialization. This overall, sialorrhea has a significant negative impact on the quality of life.
Drooling
Excessive tearing
Ptosis
Ptosis 
Trench mouth
Stuttering
Anismus
Dysphagia