Dehydration is the removal of water (Greek hydor) from an object. There are many methods of dehydration, with the most common being the application of dry heated air. This causes evaporation of the surface water, which is replaced by water internally.

Drying is often used as a method of preserving food and to obtain absolute alcohol.

In humans dehydration can be caused by a wide range of diseases and states that impair water homeostasis in the body.

Examples are :

• infectious diseases
  • yellow fever
  • cholera
  • Shigellosis
  • common gastrointestinal viral, bacterial infections resulting in vomiting and diarrhea

• external or stress related causes
  • Hyperthermia
  • shock
  • blood loss or hypotension due to trauma
  • prolonged physical activity without consuming adequate water, especially in a hot environment

• dietary imbalances due to
  • nausea
  • restricted salt diets
  • excessive consumption of alcohol

• other causes of obligate water loss or electrolyte abnormalities
  • severe hyperglycemia in diabetes. Excretion of glucose with urine (glucosuria) is accompanied with water loss. Water is the required solvent.

Symptoms may include headaches similar to what is experienced as a hangover, and lower blood pressure and a dizzy feeling when standing up which is called orthostatic hypotension. Extreme cases of dehydration can result in unconsciousness and death.

Correction of a dehydrated state is performed by rehydration, and the addition of necessary electrolytes.\n