Xerostomia and Its Causes

Overview

1. Functions of the Salivary Glands and Saliva

The salivary glands in our body, that is, the salivary glands, consist of the parotid glands, submandibular glands, sublingual glands, and minor salivary glands. The parotid glands (near the ears), submandibular glands (under the jaw), and sublingual glands (under the tongue), which are large enough to be called major salivary glands, are located in pairs on the left and right sides. The parotid glands secrete saliva into openings on both cheeks, the submandibular glands secrete into openings under the tongue, and the sublingual glands secrete into a wide area under the tongue through several small ducts.

If you imagine a situation in which there is no saliva in the mouth at all, it is easy to understand how important saliva is inside the mouth. In our body, saliva keeps the acidity (pH) in the mouth neutral and supplies the calcium and phosphate ions needed for teeth. It also protects the oral mucosa and teeth from harmful substances and lubricates the mouth, helping chewing, swallowing, and speaking smoothly.

In addition, saliva contains digestive enzymes that help digest carbohydrates, and it also contains immunoglobulins, lactoferrin, and other substances that help with antibacterial action. Saliva also acts as a solvent that dissolves taste substances. In this way, saliva plays a very important role in maintaining the health of the mouth and the entire body.

2. Xerostomia

Xerostomia is commonly called dry mouth. A healthy adult secretes about 1,000 to 1,500 mL of saliva per day, and if less than this is secreted for any reason, a person feels that the mouth is dry.

Xerostomia is known to be common enough to appear in 30% of people aged 65 and older. It occurs more often in older adults than in young and middle-aged adults. However, this is considered to be due more to medications taken or chronic diseases experienced by the patient rather than to aging itself. Of course, there are difficulties in distinguishing between the pure aging process, diseases that arise during aging, and the effects of medications taken, but studies have reported that many older adults who have lived healthy lives and are maintaining their health do not have saliva production that is very different from that of younger people. The salivary glands are organs with a large reserve capacity, and in most cases, people do not feel much discomfort until saliva production drops to about 50% or less of the normal amount. If dry mouth is bothersome enough to interfere with daily life, saliva production has already decreased significantly.

When xerostomia occurs, the dryness itself can make it difficult to swallow food and cause discomfort in speaking. In addition, the occurrence of dental caries and gum disease (periodontitis) increases and can worsen more easily, and fungal infections in the mouth, tongue pain, bad breath, and taste abnormalities may occur. Xerostomia also affects the development of oral diseases such as oral ulcers.

Causes

Xerostomia is broadly classified into two types according to its cause. One is primary xerostomia, in which dryness is caused by pathological findings in the salivary glands, such as salivary gland tumors, infections, radiation therapy, and Sjögren syndrome. The other is secondary xerostomia, in which there are no pathological findings in the salivary glands, but it occurs due to side effects from medication use, vitamin deficiencies, anemia, diabetes, and similar conditions. Let us look at the representative causes of xerostomia.

1. Medications

Medications are the most common cause of xerostomia. More than about 500 types of medications are known to reduce saliva secretion or alter the composition of saliva. In particular, among antihistamines used mainly to treat allergies and medications that act on the central nervous system (for example, antidepressants, insomnia medications, etc.), there are drugs that clearly cause xerostomia. Older adults, who most commonly complain of xerostomia, often take one or more medications that affect saliva secretion.

2. Radiation therapy

Xerostomia can also occur after radiation therapy, which is one of the treatment methods for head and neck cancer. Radiation directly destroys the salivary glands and blocks blood flow to the salivary glands, causing xerostomia. Salivary gland destruction is proportional to the amount of radiation administered and is permanent. However, in most cases, some degree of recovery occurs over 6 to 12 months, although not complete. Recently, efforts have been made to reduce salivary gland damage through various radiation therapy methods such as intensity-modulated radiation therapy.

In some cases, radioactive iodine therapy is performed after surgery as a treatment for thyroid cancer, which has been increasing recently. Xerostomia can also occur in this case. Immediately after radioactive iodine therapy, saliva secretion temporarily decreases and appears as intermittently recurring parotitis, and some of these cases progress to permanent xerostomia.

3. Sjögren syndrome

Sjögren syndrome is an autoimmune disease (a disease in which the human immune system, which protects the body from external substances, becomes abnormal and attacks itself) in which lymphocytes invade the salivary glands, lacrimal glands, and other tissues, causing chronic inflammation and secretory dysfunction. It can occur at all ages and in both sexes, but it is typically most common in middle-aged women, and the prevalence ratio of men to women is 1:9, meaning it occurs much more often in women. Sjögren syndrome is classified into primary and secondary forms depending on whether there are accompanying diseases. Secondary Sjögren syndrome refers to cases accompanied by other rheumatic diseases such as rheumatoid arthritis, systemic lupus erythematosus, and scleroderma. The main symptoms of Sjögren syndrome are findings related to reduced function of the lacrimal and salivary glands. Dry mouth, burning sensation in the mouth, dental abnormalities, voice abnormalities, dry eyes, foreign body sensation in the eyes, conjunctival redness, and sensitivity to light may occur.

4. Other causes

Xerostomia can also occur when breathing through the mouth due to nasal congestion or in a state of systemic dehydration. Xerostomia may also occur when the salivary glands are surgically removed, when nerves that innervate the salivary glands are damaged during surgery for other head and neck cancers, or when there is a congenital developmental disorder of the salivary glands. In addition, smoking, uncontrolled diabetes, chronic graft-versus-host disease, thyroid disease, hepatitis C, fear, anxiety, depression, and other psychiatric problems can also cause xerostomia.

So far, I have explained the causes of xerostomia.

In the next installment, we will look at hand, foot, and mouth disease and its risk factors.

Source: Korea Disease Control and Prevention Agency National Health Information Portal