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James L. Lewis III

, MD, Brookwood Baptist Health and Saint Vincent’s Ascension Health, Birmingham

Last full review/revision Jun 2020| Content last modified Jun 2020

Dehydration is a deficiency of water in the body.

  • Vomiting, diarrhea, excessive sweating, burns, kidney failure, and use of diuretics may cause dehydration.
  • People feel thirsty, and as dehydration worsens, they may sweat less and excrete less urine.
  • If dehydration is severe, people may be confused or feel light-headed.
  • Treatment is restoring lost water and mineral salts (such as sodium and potassium) that are dissolved in the blood (electrolytes), usually by drinking but sometimes with intravenous fluids.

(See also About Body Water.)

Dehydration occurs when the body loses more water than it takes in. Vomiting, diarrhea, the use of drugs that increase urine excretion (diuretics), profuse sweating (for example, during heat waves, particularly with prolonged exertion), and decreased water intake can lead to dehydration.

Dehydration is particularly common among older people because their thirst center may not function as well as that in younger people. Therefore, some older people may not recognize that they are becoming dehydrated. Certain disorders such as diabetes mellitus, diabetes insipidus, and Addison disease can increase the excretion of urine and thereby lead to dehydration.

Dehydration in infants and children is also common because the amount of fluid lost during diarrhea or vomiting may represent a larger proportion of their body fluids than in older children and adults.

Symptoms of Dehydration

At first, dehydration stimulates the thirst center of the brain, causing thirst, a powerful motivator for people to drink more fluids. If water intake does not keep up with water loss, dehydration becomes more severe. Sweating decreases, and less urine is excreted. Water moves from inside the cells to the bloodstream to maintain the needed amount of blood (blood volume) and blood pressure (see About Body Water). If dehydration continues, tissues of the body begin to dry out, and cells begin to shrivel and malfunction.

Symptoms of mild to moderate dehydration include

  • Thirst
  • Reduced sweating
  • Reduced skin elasticity
  • Reduced urine production
  • Dry mouth

In severe dehydration, the sensation of thirst may actually decrease and blood pressure can fall, causing light-headedness or fainting, particularly upon standing (a condition called orthostatic hypotension). If dehydration continues, shock and severe damage to internal organs, such as the kidneys, liver, and brain, occur. Brain cells are particularly susceptible to more severe levels of dehydration. Consequently, confusion is one of the best indicators that dehydration has become severe. Very severe dehydration can lead to coma.

Spotlight on Aging: Water Balance


Older people are particularly susceptible to dehydration. In older people, common causes of dehydration include

  • Confusion
  • Disorders that make obtaining fluids difficult (usually because of restricted mobility, such as after a stroke)

Additionally, older people sense thirst more slowly and less intensely than younger people do, so even those who are otherwise well may not drink enough fluids for a variety of reasons, including incontinence or the fear of incontinence.

Older people have a higher percentage of body fat. Because fat tissue contains less water than lean tissue, the total amount of water in the body tends to decrease with age.


In overhydration, the body contains too much water. In older people, the kidneys excrete excess water less efficiently, and thus older people can develop overhydration more easily than younger people do. Swelling may or may not occur.

Diagnosis of Dehydration

  • A doctor's evaluation
  • Sometimes blood tests

Dehydration can often be diagnosed from symptoms and the results of a doctor's examination. But sometimes doctors do blood tests for people who appear seriously ill or who take certain drugs or have certain disorders.

Dehydration normally causes the sodium level in the blood to increase. The reason is that although the common causes of dehydration (such as profuse sweating, vomiting, and diarrhea) result in a loss of electrolytes (especially sodium and potassium), even more water is lost, so the concentration of sodium in the blood rises.

Prevention of Dehydration

Prevention of dehydration is better than cure. Adults should drink at least 6 glasses of fluids daily (including fluid from eating foods high in water content, such as fruits and vegetables). Fluid intake should be increased on hot days, during or after prolonged exercise, and, if possible, when people have vomiting and/or diarrhea.

Exercise, a high body temperature, and hot weather increase the body’s need for water. Flavored sports drinks have been formulated to replace electrolytes lost during vigorous exercise. These drinks can be used to prevent dehydration. People should drink fluids with electrolytes before and during exercise as well as afterward. Before exercising, people with heart or kidney disorders should consult their doctors about how to safely replace fluids.

Treatment of Dehydration

  • Replacing fluids and electrolytes

For treating mild dehydration, drinking plenty of water may be all that is needed. With moderate and severe dehydration, lost electrolytes (especially sodium and potassium) must also be replaced.

Oral rehydration solutions that contain appropriate amounts of electrolytes are available without a prescription. These solutions work well to treat dehydration, especially that caused by vomiting or diarrhea in children. Sports drinks do not necessarily contain enough electrolytes to be an adequate substitute for these solutions. However, when a person is vomiting, drinking fluids may not be sufficient to treat dehydration.

More severe dehydration requires treatment by doctors with intravenous solutions containing sodium chloride. The intravenous solution is given rapidly at first and then more slowly as the physical condition improves.

Treatment is also directed at the cause of dehydration. For example, when people have nausea and vomiting or diarrhea, drugs to control or stop the vomiting or diarrhea may be used.

FAQs for Dehydration

What is dehydration?

Dehydration is when there isn't enough water in the body.

What are the signs of dehydration?

With mild dehydration, people feel thirsty and their mouth is dry. With severe dehydration, people get light-headed, confused, and dizzy when they stand up. Without treatment, people eventually go into a coma and die.

Can dehydration cause fever?

No, dehydration does not cause fever, although many disorders that cause fever can also lead to dehydration.

What causes dehydration?

Dehydration is caused when people lose more body water than they take in. So it can be caused by disorders or problems that make people lose fluid, such as gastroenteritis with vomiting and diarrhea, sweating profusely in hot weather, and uncontrolled diabetes. And dehydration can occur when people can't get enough water to drink, such as stranded travelers or older disabled people living alone.

Can dehydration cause diarrhea?

No, it's the other way around. Diarrhea can cause dehydration.

What do you do for dehydration?

For mild dehydration, drinking extra water may be all that is needed. For more severe dehydration, people should drink a special oral rehydration solution that contains the right concentration of minerals (electrolytes) and sugar. Juice, soda, and sports drinks are not as effective. For severe dehydration, doctors give people fluid through an IV.

Can dehydration cause urinary tract infection (UTI)?

No, dehydration does not cause UTI.

How do you test for dehydration?

Doctors can often diagnose dehydration without tests, but sometimes they measure the concentration of sodium and other electrolytes in the blood and test how concentrated the person's urine is.

How long does it take to recover from dehydration?

If the problem that caused dehydration is resolved and the person gets the right amount of fluid, mild to moderate dehydration can resolve in less than a day. Severe dehydration or dehydration of long duration should be treated by doctors in a hospital and typically takes 2 to 3 days to resolve with proper treatment.

How do you prevent dehydration?

To prevent dehydration, people should drink more fluid when they are working or exercising in hot weather. People should make sure that older family members have access to plenty of water when they are alone in a hot building or place. People who are not doing strenuous activity or are not in a hot environment do not need to force themselves to drink extra water when they're not thirsty.

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