Cholera rehydration nurses.jpg
Nurses encourage a patient to drink an oral rehydration solution to reduce the combination of dehydration and hypovolemia he acquired from cholera. Cholera leads to GI loss of both excess free water (dehydration) and sodium (hence ECF volume depletion—hypovolemia).
SpecialtyCritical care medicine

In physiology, dehydration is a deficit of total body water,[1] with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mild dehydration can also be caused by immersion diuresis, which may increase risk of decompression sickness in divers.

Most people can tolerate a three to four percent decrease in total body water without difficulty or adverse health effects. A five to eight percent decrease can cause fatigue and dizziness. Loss of over ten percent of total body water can cause physical and mental deterioration, accompanied by severe thirst. Death occurs at a loss of between fifteen and twenty-five percent of the body water.[2] Mild dehydration is characterized by thirst and general discomfort and is usually resolved with oral rehydration.

Dehydration can cause hypernatremia (high levels of sodium ions in the blood) and is distinct from hypovolemia (loss of blood volume, particularly blood plasma).

Signs and symptoms

Ultrasound of the blood vessels of the neck that supports the diagnosis of severe dehydration[3]

The hallmarks of dehydration include thirst and neurological changes such as headaches, general discomfort, loss of appetite, decreased urine volume (unless polyuria is the cause of dehydration), confusion, unexplained tiredness, purple fingernails and seizures. The symptoms of dehydration become increasingly severe with greater total body water loss. A body water loss of 1-2%, considered mild dehydration, is shown to impair cognitive performance.[4] In people over age 50, the body's thirst sensation diminishes and continues diminishing with age. Many senior citizens suffer symptoms of dehydration. Dehydration contributes to morbidity in the elderly especially during conditions that promote insensible free water losses such as hot weather. A Cochrane review on this subject defined water-loss dehydration as "people with serum osmolality of 295 mOsm/kg or more" and found that the main symptoms in the elderly were expressing fatigue, missing drinks between meals and bioelectrical impedance analysis.[5]

Other Languages
العربية: تجفاف
asturianu: Deshidratación
български: Дехидратация
čeština: Dehydratace
Cymraeg: Dadhydriad
español: Deshidratación
Esperanto: Dehidratiĝo
euskara: Deshidratazio
한국어: 탈수
Bahasa Indonesia: Dehidrasi
íslenska: Vökvaskortur
italiano: Disidratazione
עברית: התייבשות
latviešu: Atūdeņošanās
magyar: Kiszáradás
Bahasa Melayu: Penyahhidratan
नेपाली: जलवियोजन
日本語: 脱水 (医療)
polski: Odwodnienie
português: Desidratação
română: Deshidratare
සිංහල: විජලනය
Simple English: Dehydration
slovenščina: Izsušitev
srpskohrvatski / српскохрватски: Dehidracija
svenska: Dehydrering
Türkçe: Dehidratasyon
Tiếng Việt: Mất nước
中文: 脱水