DEAR READER: Dry mouth is a rather vague symptom and can be an indication of several disorders or side effects of certain medications or habits, such as smoking. Increased thirst can result as the body attempts to restore moisture to the mouth.

Because your letter is so short, I cannot provide a definitive answer, but based on your wording, I will give you some information about the two most likely (in my mind) candidates: Sjogren’s syndrome and diabetes insipidus.

Sjogren’s syndrome is an immune-system disorder caused by the body mistakenly attacking itself. It affects the mucous membranes and moisture-secreting glands, causing decreased production. It most commonly affects the eyes and mouth.

Risk factors include being female, over age 40, having a family history of the condition and having a rheumatic disease.

Symptoms include dry eyes and mouth, prolonged fatigue, vaginal dryness, enlarged salivary glands, persistent dry cough, skin rash, dry skin, joint pain, swelling and stiffness.

Complications of Sjogren’s include yeast infections, visual problems, dental cavities and more.

Treatment is available, but there is no cure. Mild cases can often be managed with over-the-counter eyedrops and by sipping water throughout the day to combat dry mouth. In more severe cases, prescription medications or surgery may be necessary.

Medication is available that may increase saliva and possibly tear production. An antimalarial medication has been found to be beneficial in easing symptoms of Sjogren’s. Immune-suppressing drugs such as steroids may also be used. For those with arthritis symptoms, yeast infections or other complications, medication specific to those conditions may be necessary.

When eyedrops and medications fail to improve symptoms of dry eyes, surgery to seal the tear ducts may be an option. This procedure keeps tears from draining away from the eyes, thus helping keep the eyes moist.

To help manage symptoms at home, OTC eyedrops, nasal sprays and artificial-saliva products may help. Increasing the humidity and increasing fluid intake may also be beneficial.

Diabetes insipidus (DI), despite the name, is not related to diabetes type 1 or 2. It is typically the result of the body not properly producing, storing or releasing the anti-diuretic hormone (ADH) also known as vasopressin, but it can also occur when the kidneys are unable to respond to the hormone.

The most common symptoms of DI are extreme thirst and the excretion of excessive amounts of diluted urine. Urine output can range from 2.5 liters per day for mild cases to 15 liters a day in severe cases. Normal output for healthy individuals ranges from 1.5 to 2.5 liters a day.

Diabetes insipidus is caused when the body cannot regulate its use of fluids. There are four types of DI, and each has a different way of disrupting the delicate balancing act that is involved in controlling the intake and output of fluids.

Central DI is caused by damage to the pituitary or hypothalamus gland, usually because of a tumor, illness, inflammation, surgery or a head injury. On occasion, a cause cannot be found.

Nephrogenic DI is caused by a defect in the kidney tubules, the structures that cause water to be excreted or reabsorbed. This results in the kidneys being unable to respond to ADH. The defect may be genetic or the result of a chronic kidney disorder or certain drugs.

Gestational DI occurs during pregnancy. It is caused when an enzyme made by the placenta destroys the mother’s ADH.

Finally, dipsogenic DI (primary polydipsia or psychogenic polydipsia) is caused by excessive fluid intake. When this occurs, the excess fluids suppress the ADH. This type of DI is the result of damage to the thirst-regulating mechanism within the hypothalamus, which then causes abnormal thirst. It can be the result of certain diseases, such as sarcoidosis or mental illness.

Complications of DI (excluding dipsogenic) include dehydration, dry mouth, low blood pressure, muscle weakness, weight loss, headache, fever, elevated blood sodium, rapid heart rate, sunken eyes and an electrolyte imbalance (headache, fatigue, muscle pain, irritability). Dipsogenic DI can lead to water intoxication (low blood sodium), which can cause brain damage and seizures.

Treatment depends on the severity of symptoms and the type of DI experienced. Mild cases may need only slightly increased fluid intake, while others may require medication.

Central and gestational diabetes insipidus can be treated with a synthetic hormone known as desmopressin, which acts similarly to ADH.

Nephrogenic DI cannot be treated with desmopressin, since the kidneys cannot respond appropriately because of the defect. A low-salt diet will help reduce the amount of urine made, and the medication hydrochlorothiazide (HCTZ) may be beneficial.

Dipsogenic DI has no specific treatment, since it is caused by damage to the thirst regulators and not an actual inability to regulate fluids. If mental illness is the underlying cause, treatment of the disorder may alleviate symptoms.