The lining of the mouth cavity is prone to quick drying for several reasons. It is exposed to the external environment when the mouth is opened, subjected to moving air when breathing through the mouth or talking and it does not have a waterproof layer like the skin to prevent moisture loss.
However, the body has mechanisms to counteract the risk of drying. Sometimes when these mechanisms are not sufficient or interrupted then mouth dryness will arise. A dry mouth is a symptom that may be present with many diseases and even with using certain medication. In some conditions it is more intense when sleeping and upon waking in the morning.
The moisture in the mouth is maintained by a constant supply of secretions such as mucus and saliva. These secretions arise from the salivary glands and tiny secretory cells lining the mouth. Saliva has multiple effects. Apart from moisturizing the inner lining of the mouth, it also contains digestive enzymes like amylase that acts on food entering the mouth. It also helps with lubricating the movement of food from the mouth into the throat.
Saliva also has an antimicrobial effect and prevents microbes like bacteria from causing an infection. Most of the moisture for the inner lining of the mouth comes from the saliva which is secreted by the salivary glands. The three main salivary glands are the parotid, submandibular and sublingual glands. Saliva secretion is regulated throughout the nerves that stimulate or inhibit the salivary glands.
Reduced Saliva and Moving Air
Dryness of the mouth primarily occurs for two reasons:
- Reduced saliva secretion either because the salivary glands are not sufficiently stimulated, are not able to produce sufficient saliva or there is an obstruction preventing the outflow of saliva.
- Moving air has a drying effect and the mouth cavity is unable to retain the moisture with mouth breathing, talking, coughing and other oral activities like cigarette smoking.
Therefore these two factors need to be attended to in the event of mouth dryness. It is normal for the saliva production to decrease at night when sleeping. Similarly it is normal for the mouth to dry after strenuous physical activity where mouth breathing may be necessary for short periods of time.
Behavioral or lifestyle factors like excessive talking or cigarette smoking due to the flow of air through the mouth. However, when none of these causative factors is responsible for mouth dryness, then it should be medically investigated for possible pathological (disease) causes.
Dry Mouth When Sleeping
Any of the causes of dry mouth can also be responsible for mouth dryness in the morning. However, some of these causative conditions stand out for morning mouth dryness or dry mouth after sleeping. One of the common mistakes when reporting symptoms is to confused increased thirst with dry mouth. Diabetes is one such condition where it is often said to cause a dry mouth but it is actually associated with increased thirst.
Nasal congestion is one of the more common causes of mouth dryness, especially in the morning due to mouth breathing. Even a partially blocked nose can lead to mouth dryness because a person will instinctively breathe through their mouth while sleeping since it is easier. A blocked nose can be acute, like when it commonly occurs with viral infections such as a common cold, or may be chronic like for people who suffer with perennial rhinitis.
Snoring is another common cause of mouth dryness when sleeping. It occurs when the tissue in the throat becomes loose and vibrates with the air flow during breathing. Not all snorers will be mouth breathers but many tend to breathe through their mouth. As a result the air flow through the mouth cavity results in mouth dryness which is further exacerbated by the reduced saliva secretion while sleeping.
Sleep apnea is a condition where breathing ceases for a short period of time while sleeping. There are two types – obstructive and central. Obstructive sleep apnea is the more common type and occurs when the throat tissue becomes very loose and blocks the airways. Central sleep apnea is where the brain does not send the proper signals for the breathing muscles to work as it should. Snoring often occurs in sleep apnea and the mouth dryness may occur for the same reason.
Dehydration is a condition where there is insufficient fluid intake or excessive fluid loss leading to a lower than normal level of fluid in the body. In very mild states there may be almost no symptoms apart from slight mouth dryness. Dehydration is usually pronounced with diarrhea and vomiting. However, a person who does not drink sufficient water in the day, consumes diuretics like caffeinated beverages or alcohol and is exposed to hot weather may also become dehydrated.
Mouth dryness is one the common side effects of almost all medication whether it is OTC or prescription. Morning mouth dryness may be more obvious if a person takes medication before bedtime. There are some drugs where mouth dryness is more likely to occur when it is used. This includes diuretics (“water pills”), certain antidepressants and some types of medication used for the treatment of nausea and vertigo.
Anxiety is a common cause of mouth dryness. It is usually not specific for the morning. However, awaking and recalling the possible cause of the anxiety could trigger symptoms. Sometimes mouth dryness may be due to psychological reasons. A condition known as psychogenic polydipsia is where a person is thirsty all the time. This thirst is sometimes perceived as a dry mouth, similar to increased thirst in diabetes.
Sjogren’s syndrome is an autoimmune condition where there is dryness of the mouth due to insufficient saliva secretion. It is a common rheumatologic condition that is often missed at the outset and misdiagnosed for other conditions. The mouth dryness occurs throughout the day and worsens with talking and mouth breathing. However, it may also feel worse in the morning due to a further reduction in saliva secretion with sleep.