The differential of hyposalivation significantly overlaps with that of<unk> . A reduction in saliva production to about 50% of the normal unstimulated level will usually result in the sensation of dry mouth. Altered saliva composition may also be responsible for<unk> . Physiologic Salivary flow rate is decreased during sleep, which may lead to a transient sensation of dry mouth upon waking. This disappears with eating or drinking or with oral hygiene. When associated with halitosis, this is sometimes termed "morning breath". Dry mouth is also a common sensation during periods of anxiety, probably owing to enhanced sympathetic drive. Dehydration is known to cause hyposalivation, the result of the body trying to conserve fluid. Physiologic age-related changes in salivary gland tissues may lead to a modest reduction in salivary output and partially explain the increased prevalence of<unk>  in older people. However, polypharmacy is thought to be the major cause in this group, with no significant decreases in salivary flow rate being likely to occur through aging alone. Drug induced Table 1 - Medications associated with<unk>  * Psychoactive medications such as antidepressants, opiates, antipsychotics, and medical cannabis * Antihypertensives * Bronchodilators * Proton-pump inhibitors * Antihistamines * Diuretics * Antineoplastics Aside from physiologic causes of<unk> , iatrogenic effects of medications are the most common cause. A medication which is known to cause<unk>  may be termed xerogenic. Over 400 medications are associated with<unk> , some which are listed in table 1. Although drug induced<unk>  is commonly reversible, the conditions for which these medications are prescribed are frequently chronic. The likelihood of<unk>  increases in relation to the total number of medications taken, whether the individual medications are xerogenic or not. The sensation of dryness usually starts shortly after starting the offending medication or after increasing the dose. Anticholinergic, sympathomimetic, or diuretic drugs are usually responsible. Sjögren's syndrome<unk>  may be caused by autoimmune conditions which damage saliva-producing cells. Sjögren's syndrome is one such disease, and it is associated with symptoms including fatigue, myalgia and arthralgia. The disease is characterised by inflammatory changes in the moisture-producing glands throughout the body, leading to reduced secretions from glands that produce saliva, tears and other secretions throughout the body. Primary Sjögren's syndrome is the combination of dry eyes and<unk> . Secondary Sjögren's syndrome is identical to primary form but with the addition of a combination of other connective tissue disorders such as systemic lupus erythematosus or rheumatoid arthritis. Celiac disease<unk>  may be the only symptom of celiac disease, especially in adults, who often have no obvious digestive symptoms. Radiation therapy Radiation therapy for cancers of the head and neck (including brachytherapy for thyroid cancers) where the salivary glands are close to or within the field irradiated is another major cause of<unk> . A radiation dose of 52 Gy is sufficient to cause severe salivary dysfunction. Radiotherapy for oral cancers usually involves up to 70 Gy of radiation, often given along with chemotherapy which may also have a damaging effect on saliva production. This side effect is a result of radiation damage of the parasympathetic nerves. Formation of salivary gland ducts depends on the secretion of a neuropeptide from the parasympathetic nerves, while development of the end buds of the salivary gland depends on acetylcholine from the parasympathetic nerves. Sicca syndrome "Sicca" simply means dryness. Sicca syndrome is not a specific condition, and there are varying definitions, but the term can describe oral and eye dryness that is not caused by autoimmune diseases (e.g., Sjögren syndrome). Other causes Oral dryness may also be caused by mouth breathing, usually caused by partial obstruction of the upper respiratory tract. Examples include hemorrhage, vomiting, diarrhea, and fever. Alcohol may be involved in the cause of salivary gland disease, liver disease, or dehydration. Smoking is another possible cause. Other recreational drugs such as methamphetamine, cannabis, hallucinogens, or heroin, may be implicated. Hormonal disorders, such as poorly controlled diabetes, chronic graft versus host disease or low fluid intake in people undergoing hemodialysis for renal impairment may also result in<unk> , due to dehydration.<unk>  may be a consequence of infection with hepatitis C virus (HCV) and a rare cause of salivary gland dysfunction may be sarcoidosis. Infection with Human Immunodeficiency Virus/Acquired immunodeficiency Syndrome (AIDS) can cause a related salivary gland disease known as Diffuse Infiltrative Lymphocytosis Syndrome (DILS). Similar to taste dysfunction,<unk>  is one of the most prevalent and persistent oral symptoms associated with COVID-19. Despite a close association with COVID-19,<unk> , dry mouth and hyposalivation tend to be overlooked in COVID-19 patients and survivors, unlike ageusia, dysgeusia and hypogeusia.
Xerostomia
Nosophobia
Dysphagia
Heat intolerance
Neophobia
Gastroparesis
Phonophobia
Thermophobia