Dryness of the mouth is a common symptom and may only be temporary. However if a dry mouth persists to the extent that it causes discomfort or hampers daily functioning, the cause of the mouth dryness should be investigated as it may be a symptom of a medical condition or a side effect of a drug.

The moisture within the mouth is maintained by saliva, which is  secreted by the salivary glands. Broadly, there are four types of salivary glands, located as separate structures in and around the mouth cavity or existing within the lining of the mouth cavity. The major glands are the  parotid gland, the largest of the major salivary glands, which is  located near the back of the jaw, just in front of the ear. The submandibular gland is located beneath the lower jaw, slightly in front of the parotid gland while the  sublingual gland is located under the tongue. There are hundreds of smaller (minor) salivary glands which are located within the epithelial lining of the mouth (inner cheek lining known as the buccal mucosa) and the tongue.

All these glands secrete saliva, which maintains the moisture within the mouth, lubricates the surfaces among different mouth structures, helps with tasting, assists with the initial stages of food digestion and plays an important antimicrobial role in controlling the population of microorganisms in the mouth. The amount of saliva varies during the course of the day, reducing during sleep, when stressed or anxious and increasing when eating, if hungry, by smelling certain odors or seeing certain foods.

Dryness of the mouth is primarily due to a lack of or total absence of saliva and this is known as xerostomia, although dryness of the epithelial lining may also be a result of water loss within the individual cells as well. A lack of saliva upsets the microenvironment within the mouth by :

  1. Reducing lubrication within the structures of the mouth, like the mouth lining, tongue, teeth and gum. Due to the movement within the mouth as  result of talking and chewing, these structures rub against each other and irritates the linings. This may cause tiny lacerations (cuts) within the mouth, causing pain and discomfort or leading to an infection.
  2. Increasing the chance of infections. The mouth is teeming with bacteria and even fungal spores and once the quantity of saliva is reduced, it affects the pH within the mouth. Microbes within the mouth may multiply significantly thereby  causing a wide range of mouth  infections.

Causes of Dry Mouth

There are may cases of mouth dryness which may not be related to any disease or medical disorder. These non-pathological causes are a part of daily life and occurs in every person to varying degrees.

  • Sleep. Saliva production reduces during sleep. The lack of saliva allows bacteria within the mouth to multiply while we are asleep. The bacteria then consume food particles within the mouth thereby resulting in typical bad breath in the morning.
  • Dehydration. A lack of water and electrolytes (salt) will cause dryness of epithelial lining throughout the body, including the mouth. Saliva production, like urine production, also decreases as a result of dehydration. Dehydration may be a result of drinking too little fluids, loss of fluids and electrolytes through excessive perspiration when in a hot climate and consuming large amounts of drinks that may have a diuretic effect like coffee and alcohol. Other causes of dehydration, related to disorders elsewhere in the body, may include chronic diarrhea, renal failure, UTI (urinary tract infection), or significant loss of blood.
  • Mouth breathing. The flow of air due to breathing through the mouth will cause a drying effect on the lining of the mouth. Mouth  breathing is often seen in nasal congestion, asthma and chronic obstructive pulmonary disease (COPD) like emphysema which causes gasping. Cigarette smokers also tend to suffer with mouth dryness for similar reasons as well as the effect of nicotine of the small salivary glands within the epithelial lining.
  • Excessive intake of carbohydrates – sweets, sugar,  starchy foods or refined carbohydrate products, like flour (wheat) or corn meal. These carbohydrates absorb moisture within the mouth and is the reason why fluids are usually consumed when eating foods high in starch and sugars.
  • Age-related dryness of the mouth affects the elderly and often causes difficulty with dentures. The reduced saliva is a normal physiological process associated with aging.

Causes of a dry mouth related to diseases or medical disorders, include the following :

  • Salivary gland stones cause an obstruction of the ducts of the major salivary glands. Saliva production is not impaired but the saliva cannot easily enter the mouth cavity. Typical symptoms associated with a salivary gland stone is pain during eating or when chewing. The salivary glands may become inflamed and run the risk of an infection, with a subsequent abscess formation, if left untreated.
  • Diabetes. Dry mouth is a common symptom associated with diabetes, along with other typical symptoms like increased thirst and frequent urination.
  • Autoimmune Diseases. The main autoimmune disease that causes a dry mouth is Sjogren’s syndrome. This disease affects certain glands in the body, including the salivary gland, causing inflammation and obstructing the duct that transports saliva from the gland into the mouth. Apart from a dry mouth, other common symptoms of Sjogren’s syndrome includes dry eyes, joint pains and it may be associated with other autoimmune diseases like Hashimoto’s thyroiditis. Other immune related disorders, like sarcoidosis, may also cause mouth dryness.
  • Immune Deficiency. Dry mouth is a common symptom in HIV/AIDS and is one of the contributing factors to the development of oral thrush, a characteristic opportunistic infection associated with this disease. The dryness associated with cavity linings and surfaces is not isolated to the mouth in HIV/AIDS and xerosis (dry skin) is another common symptom of HIV/AIDS.
  • Drugs. Mouth dryness is one of the most common side effects of any drug. However it is often reported when using drugs like antihypertensives (for high blood pressure), anti-Parkinsonian medication (for Parkinson’s disease), antihistamines (for allergies), corticosteroids, antidepressants, anxiolytics (for anxiety) and antipsychotics (for schizophrenia or bi-polar disorder). Chemotherapy drugs are well known for causing mouth dryness in most patients and radiation therapy to the neck or head is another common cause of mouth dryness due to therapeutic measures. Cannabis and methamphetamines, including crystal meth, may also contribute to mouth dryness, especially in overdose cases.
  • Other conditions that can cause  dry mouth include tuberculosis (TB), leprosy, amyloidosis and mumps.

Symptoms and Effects of a Dry Mouth

Dry mouth is a symptom of a medical condition, and not usually a disorder on its own. Most of the symptoms associated with a dry mouth are actually effects of mouth dryness. Persistent dryness of the mouth may result in the following effects :

  • Dental complications due to xerostomia may include repeated tooth cavities, rapid tooth decay and difficulty with the fitting and comfort of dentures.
  • Halitosis (bad breath) is a common complaint associated with persistent mouth dryness due to high bacterial growth.
  • Distorted speech may occur as a result of mouth dryness resulting in greater  friction between the structures of the mouth when talking and gives the typical tone of a ‘thick tongue’.
  • Mouth sores (oral canker ulcers) are more likely to occur due to xerostomia as a result of lacerations of the buccal mucosa (inner lining of the cheek), tongue and/or gum without the presence of saliva’s antimicrobial action. Mouth infections, like oral thrush, are also more likely when there is a persistent dryness of the mouth.
  • Polyuria or increased urine output may occur with xerostomia due to increased fluid intake.
  • Mouth dryness may also contribute towards the sensation of a lump in the throat, known as a globus sensation. In this case, there is no physical lump but the sensation can be quite disturbing.

Treatment of Mouth Dryness

Treatment of a dry mouth should be directed at the cause or any improvement will be short lived. However there are a number of drugs available to stimulate saliva production, especially for conditions like Sjogren’s syndrome, where the dryness is very pronounced. Salivary gland stones need to be removed and this should be done by a otolaryngologist (ENT specialist) as any rupture of an abscess or damage to nerves running within the gland may cause serious medical complications.

Alternatively artificial mouth moistening products may be used in toothpaste, mouth rinse, lozenge or spray form and these can be prescribed by a dentist if other conditions have been excluded. Sugar-free chewing gum is often used to stimulate saliva production as well but this is limited as the dryness may return soon after discarding the gum. Always consult with a medical doctor if you are experiencing persistent dryness of the mouth. If you suspect that your dry mouth is a symptom of a prescription drug, do not discontinue use without first discussing the matter with the supervising physician.

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Article reviewed by Dr. Greg. Last updated on May 9, 2010