Dry Mouth (Xerostomia)

Xerostomia is the subjective sensation of oral dryness resulting from reduced or absent saliva production (salivary hypofunction). Saliva is produced continuously by the three pairs of major salivary glands (parotid, submandibular, and sublingual) and by hundreds of minor salivary glands distributed throughout the oral mucosa.

Saliva plays multiple essential roles: it lubricates and protects oral mucosal surfaces, facilitates chewing and the formation of a food bolus, initiates carbohydrate digestion, assists swallowing, and provides antimicrobial protection through immunoglobulins, enzymes, and buffering capacity. Inadequate saliva production has a profound impact on oral comfort, dental health, oral mucosal integrity, taste, speech, and swallowing.

Dry mouth is not merely a minor inconvenience – chronic xerostomia causes progressive dental decay, oral mucosal atrophy, oral candidiasis, and significant impairment of swallowing and speaking. 

Medications (most common cause overall)

A wide range of commonly prescribed medications reduce salivary output by blocking the parasympathetic stimulation of salivary glands. Major categories include:

• Anticholinergic agents
• Antidepressants
• Antihistamines
• Antihypertensives
• Antipsychotics
• Opioid analgesics
• Sedatives and anxiolytics

The risk increases with the number of medications taken (polypharmacy), making elderly patients particularly susceptible.

Radiation therapy to the head and neck

• Radiation delivered to the salivary glands in the course of treating head and neck cancers causes dose-dependent acinar cell destruction and progressive salivary gland fibrosis. Xerostomia is one of the most functionally significant late adverse effects of head and neck radiotherapy. Modern radiation techniques – particularly intensity-modulated radiation therapy (IMRT), which can reduce dose to the parotid glands – have reduced but not eliminated this complication. Patients treated before the widespread adoption of IMRT may experience more severe and permanent xerostomia.

Sjögren's syndrome

• It is an autoimmune condition in which immune-mediated glandular destruction progressively impairs salivary and lacrimal (tear) gland function. It causes persistent dry mouth and dry eyes. It is more common in women and often associated with other autoimmune diseases.

Salivary gland disease and surgery

• Removal of major salivary glands reduces total salivary output
• Salivary gland infection, obstruction, or radiation injury
• Radioactive iodine (RAI) treatment for thyroid cancer can cause salivary gland inflammation and reduced function

Systemic conditions

• Dehydration (from any cause): Inadequate fluid intake, illness, or excessive fluid loss
• Diabetes mellitus: Poorly controlled diabetes is associated with reduced salivary flow
• HIV infection
• Anxiety and stress: Sympathetic nervous system activation transiently inhibits parasympathetic salivary stimulation

Mouth breathing

• Habitual mouth breathing – from nasal obstruction, sleep apnea, or habit – accelerates evaporation of oral moisture and contributes to the perception of oral dryness.

See a physician or dentist if:

• Dry mouth is persistent and not explained by temporary dehydration or a recent illness
• Dry mouth is causing difficulty chewing, swallowing, or speaking
• Dry mouth is associated with a burning sensation in the mouth, altered taste, or persistent mouth soreness
• Rapid dental decay or recurrent oral infections are occurring in the context of dry mouth
• Dry mouth develops or worsens after starting a new medication
• Dry mouth occurs in the context of head and neck cancer treatment 

A physician or dentist should evaluate persistent dry mouth to identify its cause, assess the degree of salivary impairment, and initiate measures to prevent dental and mucosal complications. Patients with salivary hypofunction require enhanced oral hygiene support, fluoride supplementation, and regular dental review.