What are the causes of hypersalivation?

Causes of Hypersalivation

Hypersalivation most commonly results from impaired clearance due to dysphagia and neurological dysfunction rather than true overproduction of saliva, though certain medications—particularly acetylcholinesterase inhibitors and cholinergic drugs—can genuinely increase salivary secretion. 1

Primary Mechanisms

The pathophysiology involves three distinct mechanisms that must be differentiated clinically 2, 3:

• Impaired clearance (most common): Reduced swallowing frequency, lingual bradykinesia, oropharyngeal dysphagia, and upper esophageal sphincter dysfunction lead to saliva pooling rather than overproduction 1, 3
• Inability to retain saliva: Hypomimia, involuntary mouth opening, declining posture, drooping head, and poor oral-facial muscle control cause apparent hypersalivation 4, 3
• True hypersecretion: Cholinergic overstimulation increases actual saliva production through muscarinic receptor activation 1

Neurological Causes

Neurological disorders are the predominant cause of clinically significant hypersalivation 1:

• Parkinson's disease: Affects approximately 50% of patients with symptomatic sialorrhea and up to 90% with subclinical findings, primarily due to impaired swallowing and reduced clearance rather than overproduction 1, 3
• Post-stroke conditions: Dysphagia leads to reduced clearance and pooling 1
• Cerebral palsy: Particularly in children with neurologically impaired oral-motor control 4, 2
• Other neurodegenerative diseases: Any condition causing decreased central control and coordination of swallowing 2, 5

Medication-Induced Hypersalivation

Acetylcholinesterase inhibitors used for Alzheimer's disease are the most common pharmacological cause of true hypersalivation 1:

• Cholinesterase inhibitors: Donepezil, rivastigmine, galantamine cause dose-dependent sialorrhea through cholinergic overstimulation 1, 6
• Pilocarpine: Direct cholinergic agonist increases salivary secretion 6
• Sedatives: Benzodiazepines and neuroleptics cause dose-dependent sialorrhea, likely through reduced swallowing frequency 6
• Clozapine and other antipsychotics: Particularly problematic in psychiatric populations 6

Oral and Anatomical Factors

Local oral conditions contribute to both production and clearance issues 1:

• Oral and gum diseases: Inflammatory conditions can stimulate salivary flow 1
• Hypotonic oral muscles: Particularly in children, leading to poor lip closure and inability to retain saliva 2, 5
• Mouth piercings: Can cause increased salivary flow as a direct complication 1

Dietary and Environmental Triggers

Acidic foods stimulate saliva production more than sugar or carbohydrate-rich foods 7, 1:

• Acidic food consumption: Increases secretion of digestive enzymes and stimulates production even at low pH 7, 1
• Physical stressors: Exercise and physical activity impact salivary flow and composition 7, 1
• Psychological stressors: Mental stress and cognitive demands affect salivary biomarkers and flow 7, 1

Systemic Disease Associations

Certain systemic conditions alter salivary function 1:

• Chronic kidney disease: Causes salivary disorders with altered composition affecting flow and consistency 1
• Acute infections: Upper respiratory tract infections within 2 weeks elevate immune markers and can affect salivary function 7

Age-Related Considerations

Age-related changes can paradoxically present with excessive salivation despite overall decreased production 1:

• Older adults may experience apparent hypersalivation due to impaired clearance mechanisms even with reduced baseline salivary flow 1
• Children with neurological impairment represent a distinct population requiring specialized evaluation 4, 2

Critical Diagnostic Distinction

Proper diagnosis must differentiate true hypersalivation from apparent hypersalivation due to impaired clearance, as this fundamentally changes treatment approach 1:

• Fiberoptic endoscopic evaluation of swallowing provides critical data for therapy selection 2, 5
• Clinical screening tools should focus on dysphagia, saliva aspiration, and oro-motor deficiencies 2, 5
• Multidisciplinary evaluation is recommended at early stages to prevent complications like aspiration pneumonia 4, 2