Dehydration is the removal of water (hydor in ancient Greek) 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.
- external or stress related causes
- dietary imbalances due to
- 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.
Even in the case of serious lack of fresh water (e.g. at sea or in a desert), drinking seawater or urine does not help, neither does the consumption of alcohol. Unnecessary sweating should be avoided, it wastes water. If there is only dry food, it is better not to eat, as it needs water to aid digestion.
A person's body loses, during an average day in a temperate climate such as the United Kingdom, approximately 2.5 litres of water. This can be through the lungs as water vapour, through the skin as sweat, or through the kidneys as urine. Some (a less significant amount, in the absence of diarrhea) is also lost through the bowels.
When taking vigorous exercise or in a hot environment, it is easy to lose twice this amount. Heavy exercise in high temperatures could cause the loss of over 2.5 litres of fluid per hour, which exceeds the body's absorptive capacity.
Judge Lynch of the Massachusetts Supreme Judicial Court argued that death by dehydration symptoms was ‘Cruel and Violent’, commenting on the 1986 Brophy Case:
- The mouth would dry out and become caked or coated with thick material.
- The lips would become parched and cracked.
- The tongue would swell, and might crack.
- The eyes would recede back into their orbits and the cheeks would become hollow.
- The lining of the nose might crack and cause the nose to bleed.
- The skin would hang loose on the body and become dry and scaly.
- The urine would become highly concentrated, leading to burning of the bladder.
- The lining of the stomach would dry out and the sufferer would experience dry heaves and vomiting.
- The body temperature would become very high.
- The brain cells would dry out, causing convulsions.
- The respiratory tract would dry out, and the thick secretions that would result could plug the lungs and cause death.
- At some point within five days to three weeks, the major organs, including the lungs, heart, and brain, would give out and the patient would die.