Normal saliva production in the mouth varies from 1 to 2 liters per day. It is the highest just before and during eating and the lowest during sleep. However, saliva production does not stop entirely at any time in the day and at least 0.5 milliliters of saliva is secreted every minute.
Saliva is mainly composed of mucus when not eating or if not stimulated by the sight, thought, taste and smell of food. This is secreted in small amounts by the buccal glands lining the mouth cavity and the sublingual and submandibular glands. When stimulated by the the presence of food in the mouth, thought of food or other sensory perceptions, saliva production increases some 20-fold. The parotid, submandibular and sublingual glands produce large amounts of serous fluid containing the enzyme ptyalin which plays a part in carbohydrate digestion. Mucus production is also increased to lubricate the food and assist with swallowing.
Various stimuli can increase saliva production, which is not due to any disease process (pathological). This includes :
- Thinking of foods that one finds tasty
- Smelling, seeing or tasting delectable foods especially when hungry
- Smooth objects in the mouth
- Nervousness, anxiety, excitement
Chewing gum or tobacco, teething and pregnancy are other causes that are not pathological. Of all the taste sensations, sour taste and the so called ‘umami’ taste are most likely to trigger the production of copious amounts of saliva.
The process of saliva production, factors that affect salivation, as well as the functions of saliva are discussed further under Saliva Secretion.
Saliva in the Mouth
Saliva is drained out of the mouth cavity by swallowing and it passes down the throat and esophagus and into the stomach. Two possible causes may result in hypersalivation :
- Excessive saliva production (polysialia)
- Inadequate drainage of saliva, often related to swallowing problems (more frequently dysphagia which is difficulty swallowing)
In most cases, excess saliva may be swallowed but if drooling is present, it may be an indication of difficulty swallowing.
Causes of Excessive Saliva in the Mouth
The causes of impaired saliva drainage from the mouth are discussed under oropharyngeal dysphagia. Profuse salivation may be a result of one or more of the following causes :
- Dental prosthetics – new and ill-fitting implants, bridges and dentures.
- TMJ dysfunction
Water brash is the term for sudden excessive salivation due to regurgitated gastric contents.
- GERD (gastroesophageal reflux disease)
Inflammation and Infection
- Mouth inflammation (stomatitis)
- Upper respiratory tract infections
- Rare infectious causes :
- Any severe pain, especially if of sudden onset
- Mouth pain (stomatodynia)
- Facial nerve – Bell’s palsy
- Trigeminal neuralgia
- Geniculate neuralgia
Medication and Illicit Substances
Use or overdose of the following medication and substances :
- Parasympathomimetics, also known as cholinergic drugs, for conditions like hypertension
- Psychoactive drugs
- Nicotine toxicity
Medication that causes a dry mouth may result in hypersalivation when discontinued (rebound effect). However, in many cases, the restoration of normal salivary flow is initially mistaken for profuse salivation.
- Metal poisoning – mercury and arsenic poisoning being the most prominent.
- Bites (insect, reptiles) – neurotoxic venom causes both dysphagia and hypersalivation
- Mushroom poisoning