Dry Mouth (Xerostomia): Causes and What Helps

Xerostomia is the subjective feeling of dryness in the mouth. Hyposalivation (salivary gland hypofunction) is an objectively reduced production of saliva, measured in the surgery. The two do not always go together: some people feel dry despite normal salivary flow, while others have markedly reduced secretion without complaining of it. A change in the composition of saliva (thicker, stickier) can give a feeling of dryness without a large drop in volume.

This distinction has practical significance, because the risk of decay depends above all on the actual amount and quality of saliva, not on sensations. That is why a dentist can measure resting and stimulated salivary flow, and if a general disease is suspected, a doctor will order further tests.

The scale of the problem is large. A meta-analysis of 128 publications and nearly 175 thousand people over 60 (excluding people with diseases known to cause dryness and those after radiotherapy) estimated that xerostomia occurs in about 32.4% (95% CI 29.6–35.2%), and hyposalivation in about 33.0% (95% CI 25.7–42.0%) of older adults. The authors stressed, however, very high heterogeneity between studies and a high risk of bias in most of them, so the figures should be treated as approximate.

For the reader the conclusion is practical: if dryness appeared after starting a new drug or increasing a dose, the drug is the prime suspect. Groups often named include drugs with anticholinergic action, antidepressants, antihistamines, diuretics, some hypertension drugs and drugs for overactive bladder. The risk rises when several such drugs are taken at once, which is common in older people.

Diabetes is one of the more common general diseases associated with dryness. A meta-analysis of 22 observational studies (1,202 people with diabetes, 946 without disturbed glycaemia) showed that in adults with diabetes unstimulated salivary flow was lower by about 0.13 ml/min (95% CI 0.06–0.2) and stimulated flow by about 0.44 ml/min (95% CI 0.13–0.75), salivary pH was lower and urea concentration higher. The authors rated the certainty of evidence as low, because of the type of studies. The result agrees with clinical experience: dry mouth, along with excessive thirst and frequent urination, can be one of the symptoms of poorly controlled blood glucose. We write about diabetes in our knowledge base.

Dehydration (insufficient drinking, fever, diarrhoea, heat, excessive fluid loss) reduces saliva secretion, but usually resolves once fluids are replaced. Other causes include infections of the salivary glands, hormonal disorders and some general diseases; stress and anxiety can also temporarily cause a feeling of dryness. Tobacco smoking, alcohol and a lot of caffeine intensify the feeling of dryness, although their effect on actual saliva secretion may be smaller than it seems.

In people in whom dryness appeared suddenly, and is accompanied by swelling of the salivary glands, difficulty swallowing or recurrent infections, one should not assume it is 'just the medication'. Such a picture needs medical assessment, because it may point to a salivary gland disease or an autoimmune disease.

Dryness on waking often results from mouth breathing at night: the stream of air dries the mucous membrane, and salivation at night is naturally minimal. Typical causes are nasal blockage (a cold, a deviated septum, swollen mucosa), snoring and sleep apnoea. An assessment by an ENT specialist can help if the problem mainly affects the mornings.

Data from a prospective study comparing 60 adults with newly diagnosed sleep apnoea-hypopnoea syndrome with 54 healthy people show the scale of the problem: dryness on waking occurred in 45% of people with sleep apnoea versus 20.4% in the control group, and during the day in 21.7% versus 9.3%. The frequency of dryness was higher in moderate than in mild apnoea and depended on BMI. Surprisingly, among people with sleep apnoea, dryness on waking was more common in those using CPAP (57.1%) than in those not treated with it (16.7%; p = 0.008).

Why might CPAP dry out the mouth? The most commonly cited cause is air leaking through the mouth with a nasal mask, leading to a flow of dry air through the mouth; a humidifier, a mask fitted by a specialist or a different type of mask help. This explanation is widely used in practice, but the study described above did not test this mechanism. People who use CPAP and have dryness should discuss it with the doctor managing their apnoea treatment. We write about sleep apnoea in our articles on symptoms and diagnosis and on alternatives to CPAP.

Sjögren's syndrome is an autoimmune disease in which the immune system attacks the lacrimal and salivary glands. The typical picture is dry mouth together with dry eyes, often with joint pain and fatigue. We describe it in detail in our article on Sjögren's syndrome. Among all the treatment options for dryness in this disease, the best documented is pilocarpine: in a review of 36 studies with 3,274 patients, high-quality evidence indicated that pilocarpine is better than placebo at reducing dryness symptoms, and moderate-quality evidence that it increases salivary flow; adverse effects were common.

In a large randomised trial from 1999 (373 patients with Sjögren's syndrome), pilocarpine at 5 mg four times a day for 12 weeks improved symptoms of dry mouth and dry eyes compared with placebo, and salivary flow rose 2–3-fold after the first dose; the most common adverse effect was sweating. Pilocarpine is a prescription drug with cholinergic action and has contraindications, so the decision to use it belongs to the doctor.

Radiotherapy involving the salivary glands (treatment of head and neck cancers) often causes lasting damage to the glands. The 2021 ISOO/MASCC/ASCO guideline indicates that for prevention the strongest evidence concerns tissue-sparing radiation techniques, and for treating symptoms — mucosal moisturising preparations, artificial saliva and agents that stimulate salivation; after radiotherapy, oral pilocarpine or cevimeline, acupuncture or transcutaneous electrostimulation may be considered. People after head and neck radiotherapy are at very high risk of decay and should remain under constant dental care.

That does not mean moisturising preparations are useless — rather that the evidence is weak and the products very varied. A later review of 10 studies from 2019 indicated that all the tested artificial saliva products reduced dryness symptoms, but the studies had a high risk of bias, and a 2025 umbrella review (48 papers, over 80% rated 'critically low' quality) concluded that substitutes and saliva stimulants act mainly as moisturisers, with a short-term effect.

In practice this means a pragmatic approach: try several types (spray, gel for the night, sugar-free lozenges or gum) and stay with what helps you. Sugar-free gum or lozenges stimulate salivation in people who have kept a reserve of it, and are named in oncology guidelines. As for xylitol: its proven role concerns limiting decay (see our article on xylitol and tooth decay, in which we assess it cautiously), not directly treating dryness. It is a sensible sweetener in gum and lozenges, but not a 'cure for dryness'.

Saliva is the teeth's main natural defence, so its absence increases the risk of decay, including decay at the tooth necks and roots, and of oral thrush. A narrative review on patients with head and neck cancer describes chronic hyposalivation as a risk factor for demineralisation and rapidly progressing cavities that can lead to tooth loss; the use of fluoride reduces but does not eliminate this risk. In a cross-sectional study of 225 people with salivary gland hypofunction, patients with Sjögren's syndrome had more cavities (odds ratio 1.72; 95% CI 1.03–2.88) than people with hypofunction from other causes.

Remember that dry mouth is not only a discomfort but also a risk factor that can be modified. Early identification of the cause and regular dental check-ups are the best protection. We write about the ageing of the oral microbiome in our knowledge base.

Dry mouth is worth taking seriously, but calmly. The first step is a review of medicines and checking that the symptom did not begin after a change of therapy; the second, excluding simple causes (nasal blockage, dehydration, mouth breathing); the third, in suspected general disease (diabetes, Sjögren's syndrome), appropriate diagnostics. In parallel the teeth must be protected, because they pay the highest price for the lack of saliva.

As for symptomatic treatment, it is honest to admit that the evidence for moisturising preparations is weak, but using them is safe and brings relief to many people. Pilocarpine has the best evidence in Sjögren's syndrome, but it is a prescription drug. The rest is sensible habits: water, sugar-free gum, fluoride and frequent check-ups.