Dry mouth, also known as xerostomia, is a common condition that everyone experiences. A dry mouth occurs when there is not enough saliva to keep your mouth moist. Saliva is produced by salivary glands located in or near the mouth. These glands connect to the mouth by a thin tube, called a duct, through which saliva flows.
There are a number of causes of xerostomia. Most produce a dry mouth during both the day and night, but the dryness is often most noticeable when waking up in the morning. Breathing through the mouth and not drinking while asleep are two reasons why a dry mouth is often worse in the morning.
The human body is designed to breathe primarily through the nose. Air enters the nose, where it is warmed and moistened before traveling down the throat and into the lungs.
When a person breathes through the mouth, tissues within the mouth must perform these functions, transferring moisture to the air. When saliva production is unable to keep up with this moisture loss, the mouth becomes dry.
Any condition that prevents nose breathing can produce xerostomia. Nasal congestion due to the common cold or allergies is a common cause of mouth breathing. Congestion often worsens when lying down, so mouth breathing increases when sleeping.
Even when the nose is not blocked, people tend to breathe more through their mouth during sleep. This occurs because sleep relaxes the jaw muscles, opening the mouth.
Salivary Gland Disorders
Disorders of the salivary glands may produce a dry mouth. Sjogren syndrome is an autoimmune disease in which the salivary glands are destroyed by a person's own immune cells, producing xerostomia.
Dry eyes occur as well, as the lacrimal glands — which produce tears — are also destroyed. Radiation therapy for head and neck cancer usually damages the salivary glands as a side effect, producing xerostomia. Salivary gland function also declines with age, which is one reason why dry mouth tends to be more common in older people.
Dehydration and Dry Environment
Anything that causes dehydration will reduce the water content of body tissues. The mouth is no exception, so a dry mouth is common with dehydration.
Dehydration, and thus xerostomia, is often worse in the morning, after many hours of not drinking while asleep. Poorly controlled diabetes mellitus is a common cause of dehydration, as high blood sugar levels increase urine production by the kidneys.
Being in an environment with dry air further increases the possibility of a dry mouth, especially during mouth breathing. The drier the air, the more moisture that must be transferred to it from tissues in the mouth.
Medications, Smoking and Alcohol
Hundreds of prescription and over-the-counter medications can produce a dry mouth, according to the National Institute of Dental and Cranial Facial Research. Antihistamines and various antidepressants and antianxiety drugs are common causes of dry mouth.
Illegal drugs, such as methamphetamine, can also produce xerostomia. Some chemotherapy drugs reduce saliva production, which usually improves when they are stopped.
Alcohol increases urine production, which can lead to dehydration and a dry mouth. It also has some muscle relaxant effects, which can promote jaw opening during sleep. Tobacco use can directly reduce saliva production, according to Merck Manual.
Dry mouth upon awakening may be caused by obstructive sleep apnea, a condition in which the throat intermittently closes during sleep, preventing air from entering the lungs. When this occurs, the body automatically responds by opening the mouth.
Repeated mouth opening, sometimes hundreds of times per night, can lead to a dry mouth. In a study published in "Journal of Sleep Research" in September 2006, 31 percent of people with obstructive sleep apnea reported awakening almost all of the time with a dry mouth. Only 3 percent of people without sleep apnea reported the same thing.
Certain autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus and scleroderma, may produce xerostomia. In some people, this occurs because they also have Sjogren syndrome. In others, the dry mouth has no apparent cause or is due to salivary gland inflammation related to their autoimmune disease.
Seeking Medical Attention
See your doctor if you frequently notice a dry mouth in the morning. Your doctor will help determine the cause and appropriate treatment. Lifestyle changes may be recommended, such as stopping smoking, reducing alcohol consumption, taking frequent drinks of water or other sugarless fluids and chewing sugar-free gum.
Using a humidifier at night will moisten the air and may reduce the likelihood of a dry mouth in the morning. Substituting medications for alternatives that are less likely to produce a dry mouth may be tried.
If a medical condition is responsible, treatment of the underlying condition may improve the dry mouth. Your doctor may also recommend specific treatments to increase moisture in the mouth, including mouthwashes designed for dry mouth or medications that stimulate saliva production, such as pilocarpine (Salagen).
Reviewed and revised by Mary D. Daley, M.D.
- National Institute of Dental and Craniofacial Research: Dry Mouth
- Stanford University: Sleep Apnea Information and Resources
- Dry Mouth: A Clinical Guide on Causes, Effects and Treatments; Guy Carpenter, et al.
- Journal of Sleep Research: Dry Mouth Upon Awakening in Obstructive Sleep Apnea
- Merck Manual Professional Version: Xerostomia