Saliva is continuously produced from four pairs of salivary glands: the parotids, mandibulars, sublinguals, and zygomatics. The salivary glands receive excitatory input from the salivary nuclei, located in the brain stem, after taste and tactile stimuli are received from the tongue and other areas of the mouth. Higher centers in the central nervous system may also have an excitatory effect, resulting in ptyalism in response to conditioned reflexes (Pavlovian response). Ptyalism is a common response of the dog to imminent feedings and elevated ambient temperature. In the cat, ptyalism can accompany purring.

The saliva of dogs and cats has no significant enzyme content, but saliva still performs a number of important functions. It facilitates swallowing by softening and lubricating food, as well as, protecting the oral, pharyngeal, and esophageal mucosa during the passage of the food bolus into the stomach. The evaporation of saliva is an important mechanism of heat loss for the dog.

Pseudoptyalism, an overflow of saliva from the oral cavity, occurs when an animal is unable or unwilling to swallow. The first consideration for any dog or cat with this clinical sign is rabies. Pseudoptyalism can also result from conformational disorders of the lips and mouth (most often seen in giant-breed dogs), diseases causing oral deformity, disorders of the lips, or disorders of swallowing. Finally, oral foreign bodies are a common cause of this condition.

Ptyalism can be seen with inflammatory or painful oropharyngeal lesions, such as periodontal disease, stomatitis, gingivitis, glossitis, faucitis, pharyngitis, and esophagitis. Disorders of the stomach and small intestine may cause ptyalism by causing pain or nausea. Drooling is common feature of vomiting.

Various medications and toxins may cause ptyalism by irritating the oral mucosa (caustics). Agents such as thallium, metaldehyde, cresol, household cleaning products, secretions of various toads and newts, and certain plants (Amanita mushrooms, nettles, dumbcane, philodendron, dieffenbachia, poinsettia, and Christmas trees) create ptyalism. Oral medications in cats can result in copious amount of saliva. Other medications, such as apomorphine, cause nausea and vomiting by stimulating the chemoreceptor trigger zone or the vomiting center in the midbrain. Organophosphate toxicity can result in cholinergic signs (parasympathetic stimulation), such as ptyalism. Overdoses of D-limonene (citric oil insecticides), ivermectin, fluids containing a benzoic acid derivative, caffeine, amphetamines, cocaine, and opiates may also cause hypersalivation.

Causes of ptyalism secondary to neurologic disorders include lesions of the trigeminal nerve (inability to close mouth) and the facial nerve (inability to move the lip). Lesions of the glossopharyngeal, vagus, and hypoglossal nerves result in loss of the gag reflex or the inability to swallow. Precautions are needed if rabies virus is at all suspected. Neuromuscular and muscular disorders (e.g., myasthenia gravis) resulting in dysphagia can lead to secondary hypersalivation.

Uremia and hepatoencephalopathy can result in oral gastrointestinal tract ulcers, hyperammonemia, and increases in other nitrogenous wastes that may cause nausea and subsequent ptyalism.

Phenobarbital-responsive ptyalism is thought to be a form of limbic seizures and is usually characterized by episodic ptyalism, enlarged and sometimes painful salivary glands, and intermittent dysphagia, retching, or vomiting (Gibbon et al. 2004).

Information obtained from a thorough history, physical examination, and careful observation of the patient should help prioritize rule-outs (i.e., ingestion of caustic agents, abnormal mastication of food, dropping food from mouth, blood-tinged saliva, and evidence of systemic disease). If rabies is excluded, a thorough examination of the oral cavity, neck, temporal mandibular joint, regional lymph nodes, and salivary glands should be completed. After ruling out systemic or metabolic disorders, sedation or general anesthesia may be required to adequately examine the oropharyngeal cavity. Also, other diagnostic modalities can be utilized during chemical restraint if indicated, such as biopsies of masses, dental radiography, and endoscopy, to name a few. The presence of concurrent clinical signs should help further localize the cause of the ptyalism. For example, vomiting, retching, regurgitation, weight loss, and anorexia may indicate metabolic or gastrointestinal disease. Clinical signs consistent with the central nervous system—mental dullness, head pressing, seizures, disorientation—may indicate hepatoencephalopathy. Gagging, retching, regurgitation, and coughing may indicate oropharyngeal or esophageal disorders.