Continuous Positive Airway Pressure (CPAP) therapy is a widely adopted and highly effective treatment for obstructive sleep apnea. The CPAP machine delivers a steady stream of pressurized air through a mask to keep the upper airway open. A common side effect reported by users is xerostomia, the medical term for dry mouth. This dryness, which can lead to a sore throat or hoarseness upon waking, is frequently a direct result of the therapy itself.
Why CPAP Use Leads to Dry Mouth
The primary reason CPAP therapy causes dry mouth is the interaction between the pressurized airflow and the oral cavity. Air moving across the mucous membranes of the mouth and throat rapidly evaporates natural moisture and saliva, leading to a parched feeling. This effect is dramatically worsened when a user breathes through the mouth while wearing a nasal mask, as the air intended for the nasal passages is shunted out of the mouth, causing it to dry out quickly.
A poorly fitting mask is a major contributor, as air escaping around the edges (a mask leak) can be directed toward the mouth or reduces the overall humidity reaching the user. Furthermore, the continuous positive pressure from the machine may physically impede the natural flow of saliva. CPAP pressures, which typically range from 6 to 14 cmH₂O, can be higher than the pressure needed for saliva to exit the ducts, essentially blocking its release and leading to reduced lubrication.
Equipment and Device Solutions
The most effective equipment solution involves incorporating a heated humidifier into the CPAP setup, which adds moisture to the pressurized air before it reaches the user. Most modern CPAP machines include a built-in humidifier with adjustable temperature and humidity settings; increasing these can prevent the air from drying out the nasal and oral passages. If the air is humidified but still feels cool, using heated tubing maintains the air temperature from the machine to the mask, preventing moisture from condensing prematurely (rainout).
Ensuring a proper mask fit is paramount, as an air leak reduces therapy effectiveness and directs dry air over the mouth and face. Users should check the mask seal in their typical sleeping position, but avoid overtightening the headgear, which can distort the mask cushion and create more leaks. For individuals who cannot stop breathing through their mouth, switching from a nasal mask to a full-face mask, which covers both the nose and mouth, ensures the pressurized and humidified air is delivered regardless of the breathing route.
A chin strap can be used with a nasal mask to gently support the jaw and keep the mouth closed during sleep. This accessory promotes nasal breathing, stopping the air from escaping and drying the mouth. If dryness persists, a sleep specialist may need to review the CPAP pressure settings, as excessively high pressures can exacerbate mask leaks and mouth breathing.
Managing Oral and Behavioral Factors
Users can manage dry mouth symptoms by focusing on hydration and oral care habits. Increasing daily water intake is an effective strategy, particularly in the hours leading up to bedtime, as dehydration magnifies the sensation of oral dryness. Keeping a glass of water nearby to take small sips during brief awakenings can also provide immediate, temporary relief.
Specialized over-the-counter products designed for xerostomia offer targeted symptom management. These include moisturizing oral sprays, gels, or lozenges that contain ingredients like xylitol or synthetic saliva to coat and lubricate the mouth’s tissues for several hours. Maintaining excellent nightly oral hygiene is important, as a lack of saliva reduces the mouth’s natural defense against bacteria, increasing the risk of cavities and gum disease. Finally, users should review all current medications with a healthcare provider. Many common drugs, such as antihistamines and decongestants, list dry mouth as a known side effect that can compound the effects of CPAP therapy.