Dehydration is the excessive loss of water and electrolytes (minerals that help maintain fluid balance) from the body. Water and electrolytes are essential to support normal body functioning.

Dehydration can quickly progress from mild to moderate to severe within hours, especially in infants and young children. Dehydration may involve primarily water loss, primarily electrolyte (e.g., sodium) loss, or the loss of equal amounts of both. Determining the specific fluid/electrolyte imbalance that is present can help ensure that appropriate replacement fluids are used.

Symptoms of mild dehydration may include thirst, headaches and dark yellow urine. Moderate cases of dehydration may include dry mouth, little or no urine, sluggishness, a rapid heartbeat and lack of skin elasticity. Severe dehydration, a life-threatening condition, is characterized by extreme thirst, no urine or tears, rapid breathing, an altered mental state and cold, clammy skin.

Mild dehydration is common, and usually caused by not drinking enough fluids throughout the day. Fluids are continuously lost through normal body functions such as sweating, breathing and urinating. Illness (e.g., diarrhea, vomiting), physical activity and climate conditions (e.g., heat and humidity) can cause fluid loss and increase the risk of dehydration. Certain populations are at higher risk of developing moderate to severe dehydration. These include infants and small children, people with chronic illnesses and the elderly.

Physicians can usually identify dehydration after compiling a medical history (including a discussion of the patient’s symptoms) and performing a physical examination. Urine and blood tests may be used to confirm the diagnosis.

Treatment in mild cases of dehydration often involves drinking adequate amounts of water and eating foods with high water content. Other types of fluids may also be used. In some moderate to severe cases of dehydration, the use of intravenous (I.V.) fluids and hospitalization may be necessary.

Dehydration is the excessive loss of body fluids (water, along with electrolytes). Water makes up approximately 60 to 70 percent of an adult’s body weight (and a higher percentage in infants and children). Electrolytes are minerals the body needs to help maintain the balance of fluids. The major electrolytes include sodium, potassium, magnesium, phosphates, chloride and calcium.

Water is necessary for all of the body’s functions. Among its roles, water is essential to digestion, metabolism, regulation of body temperature, as well as carrying waste out of the body, maintaining blood pressure and helping cells communicate. Unlike food (which a healthy person can live without for weeks) an adult without water will die in four to five days.  

Water and electrolytes move freely in and out of cells (osmosis) according to a delicate balance primarily regulated by the kidneys and hormones (chemical messengers that regulate the body’s activities). When cellular fluid imbalances occur, the body automatically responds to restore the balance. For example, if there is too much sodium inside the cell, the body will send water inside to restore the proper balance of water and sodium. If there is too much water inside a cell, and not enough of other electrolytes, the body will restore balance by sending water out of the cell into the area between cells.

The body continually makes quick, automatic adjustments to achieve fluid balance. This constant maintenance of the balance of body fluids is called homeostasis.

However, water is not stored in the body and must be replenished to make up for its loss. Normally, about 10 cups (2.4 liters) of fluid are lost daily through:

• Urination (60 percent)
• Breathing and perspiration (35 percent)
• Stool (5 percent)

Fluid lost through breathing and regular perspiration is known as insensible water loss because people are essentially unaware of this process as it happens. Conditions that produce additional water and electrolyte loss include diarrhea, vomiting, intense sweating and breastfeeding.

The daily amount of water needed may vary from person to person. Hydration needs may be based on factors such as a person’s health, level of physical activity and climate. A rough guideline for healthy adults is about 8 to 12 cups a day from all sources. If bodily fluids are lost at higher than normal amounts due to illness or excessive sweating, then extra fluids are needed to replace those that are lost.

Urine output is the easiest way for most people to know if the body is adequately hydrated. Normal urine from a well-hydrated person will be abundant and appear clear or pale yellow. Infants who are well-hydrated will wet a diaper approximately every three hours (about eight diapers per day). If urine output decreases or becomes dark yellow, it is a signal that the body is becoming dehydrated.

Thirst is another signal that the body needs fluid. However, by the time a person experiences thirst, mild dehydration has already begun. Therefore, it is important to take in an adequate amount of fluids and food, and not rely solely on thirst to determine when to drink.

When not enough fluids are taken in to replace fluids lost, dehydration develops. As dehydration sets in, there is not enough water to move back and forth between cells in order to restore balance of body fluids. This lack of water can affect the entire body.

The heart pumps harder to maintain adequate blood flow to the organs. Blood pressure lowers as fluid levels diminish. Reduced blood flow to the skin and reduced levels of water keep the body from perspiring and dissipating heat. The distribution of nutrients the body needs and elimination of wastes becomes impaired. A person’s weight begins to drop rapidly as the body literally dries out. Eventually, the kidneys and other major organs begin to fail. Blood clots can form as the water content of blood is reduced. A person can develop seizures, slip into a coma and will eventually die without emergency intervention.

When dehydration develops from heat-related causes, additional complications may include heat exhaustion and heat stroke (a potentially fatal condition that requires immediate emergency intervention).

Dehydration is cumulative and often increases gradually over time if fluid loss is not replaced adequately. In those at higher risk (e.g., infants, small children, the elderly), dehydration can become moderate to severe in as little as 24 hours. Worldwide, severe dehydration caused by vomiting and diarrhea is a leading killer of children. In the United States, few infants and children develop severe cases of dehydration due to easy access to replacement fluids and medical care.

In addition, the more body fluid lost, the longer it takes to make up the deficit. The dehydrated body can only absorb so much fluid at a time, and needs time to reabsorb water gradually. The kidneys may no longer work efficiently due to dehydration and may be unable to quickly process the fluid received, which can lead to edema (excessive fluid retention). This type of fluid imbalance is the opposite of dehydration, and can also be harmful. In cases of moderate to severe dehydration where intravenous (I.V.) fluids are necessary, medical personnel closely monitor patients to ensure the kidneys are working properly and that the body can handle the reintroduction of fluids. If the body shows signs of fluid overload during rehydration, the rate of replacement is slowed.

Dehydration can be mild, moderate or severe. This is determined by the percentage of body weight lost due to fluid loss. Normally, the body loses and regains one to two percent of its weight throughout the day as fluids are continually eliminated and replaced. When dehydration occurs, a higher percentage of body weight is lost. Dehydration can progress from mild to moderate to severe within hours, especially in infants and children. Weight loss of more than 15 to 20 percent is considered a medical emergency and can result in death without emergency intervention.

Dehydration may be classified as follows:

Dehydration may be further defined by the type of fluid/electrolyte imbalance that exists. Knowing which type of imbalance is present in moderate to severe cases of dehydration can ensure that appropriate replacement fluids restore the proper balance of fluids and electrolytes to the body. These types of dehydration include:

• Isotonic dehydration. When both fluid and sodium are lost in equal amounts. It is most common in people taking diuretics (medications that increase urine output), fasting, or people with severe or prolonged diarrhea and vomiting. This accounts for approximately 70 to 80 percent of all pediatric cases of dehydration. This type of dehydration is sometimes referred to as isonatremic dehydration.
  
  
• Hypertonic dehydration. When more fluid than sodium is lost. This is more common in people not getting enough nutrients through their diet (e.g., due to watery diarrhea, excessive vomiting, breastfeeding, eating disorders) or who have diabetes insipidus (water diabetes, which is characterized by frequent urination and thirst). It may also be due to excess diuretic use, infection or fever. It accounts for approximately 10 to 20 percent of all pediatric cases of dehydration with diarrhea.
  
  Hypertonic dehydration is considered the most dangerous of the three types because of the risk of complications. Patients may seem less ill at first and often are not brought in for treatment until the dehydration has become more severe. There are also risks associated with treatment (e.g., rapid rehydration can lead to cerebral edema). This type of dehydration is sometimes referred to as hypernatremic dehydration.
  
  
• Hypotonic dehydration. When more sodium than fluid is lost. This type of dehydration is sometimes referred to as hyponatremic dehydration, and accounts for approximately 10 to 15 percent of all pediatric cases of dehydration with diarrhea. This may occur due to the use of diuretics or kidney disease. Although rare, it can also occur due to drinking too much water, which excessively dilutes the level of sodium in the body and may cause the body’s cells to swell (dilutional hyponatremia). This complication can be life-threatening if swelling causes pressure on the brain (cerebral edema).

Dehydration may be caused by many different factors, any of which can contribute to lost fluids not being adequately replaced in the body. Most people never progress beyond mild dehydration because eating and drinking can resolve the condition. However, some people are more likely to develop more serious levels of dehydration due to certain medical conditions or situations that interfere with their normal intake of water.

Inadequate intake of fluids is one cause of dehydration and is usually responsible for mild cases. This may occur during illnesses that affect the throat (e.g., strep throat, tonsillectomy), making swallowing difficult. Some people may become dehydrated prior to medical testing or surgery, when a physician restricts liquids or food ahead of time.

People who deliberately restrict their food or fluid intake are also at higher risk of dehydration. This includes people with eating disorders (such as anorexia nervosa) and people who fast for religious or political reasons. People with certain physical disabilities may be unable to get adequate nutrition, including sufficient fluids. Others may deliberately withhold fluid intake to avoid frequent urination if going to the toilet is cumbersome due to their disability. Severe dehydration can result when people experience water and food deprivation in extreme survival conditions.

Basically, dehydration is likely to occur any time fluids are lost in excessive amounts (and not replaced). Fluid loss may be caused by a variety of factors, including:

• Gastrointestinal fluid loss:
  
  
• • Diarrhea. One of the most common causes of dehydration. Diarrhea may be caused by bacteria, viruses or parasites. Infants, children and the elderly are especially at risk for dehydration due to diarrhea because weak immune systems make them more vulnerable to illnesses that can cause diarrhea.
    
    
  • Vomiting. The rapid loss of bodily fluids that occurs with vomiting makes dehydration more likely to occur. Certain populations are at higher risk of dehydration from this cause, including infants and children, the elderly, people with eating disorders (e.g., bulimia nervosa) and anyone taking medications that can cause vomiting.
    
    
• Excessive urination:
  
  
• • Certain medications that increase urination beyond normal levels (e.g., diuretics).
    
    
  • Conditions that affect kidney function. Kidneys regulate the loss of body fluid through urine. Conditions that may affect urine production include diabetes mellitus, diabetes insipidus (water diabetes, which is characterized by frequent urination and thirst) and kidney cancer.
    
    
• Excessive fluid loss through the skin (perspiration) and lungs (breathing):
  
  
• • Heat and/or humidity. Of the two, humidity plays the greater role in dehydration because it interferes with the body’s ability to cool itself. In humid areas, sweat drips from the body rather than evaporates, so the lost fluid does not contribute toward cooling the body (the normal function of sweat). The elderly, infants and children are especially at risk for dehydration and other complications due to heat and humidity (e.g., heat exhaustion and heat stroke).
    
    
  • Physical activity. Excessive sweating can occur during sports or other vigorous physical activity and also adds to the risk of dehydration.
    
    
  • Fever or burns, including sunburn. These conditions increase body temperature, requiring more fluid for proper body functioning. Burns may inhibit the skin’s ability to draw in moisture as well as sweat, which can prevent the body from cooling down and increase the risk of dehydration.
    
    
  • Air travel and high altitudes. Commercial airplanes maintain dry air in the cabin interior, with levels as low as 1 percent humidity. Because there is less moisture in the air, additional water from other sources is needed to avoid dehydration. This is especially true on long flights or at high altitudes (8,000 feet or higher).

Signs and symptoms of dehydration may vary, depending on the severity of fluid loss experienced. It is important to note that the body’s need for water is constant and not accompanied by symptoms such as thirst. By the time a person feels thirsty, they have already developed mild dehydration.

Diagnosing dehydration often begins with a medical history. A physician may ask questions about any recent illnesses, conditions or activities that may increase the risk of dehydration. A physical examination is also performed, which may include taking the patient’s temperature, blood pressure, heart rate, and examining the condition of the patient’s skin.

Certain tests may be performed to confirm a diagnosis of dehydration, including:

• Urine test. A urine sample is analyzed in a laboratory to identify whether dehydration exists and whether it is mild, moderate or severe. This is done by checking urine color, clarity and whether certain carbon compounds are present. The volume of water in urine, specific gravity, may also be determined.
  
  
• Blood test. Blood is drawn to identify electrolyte (e.g., sodium, potassium) and blood concentration levels in the body, both of which may indicate a fluid imbalance. Blood tests may also be used to evaluate kidney function, which can affect urine output.

It is important to know when to seek medical attention for dehydration. Certain people should seek medical attention for even mild symptoms of dehydration. This includes infants, small children, the elderly and women who are pregnant or breastfeeding. People with certain medical conditions or taking certain medications may also be advised by their physician to immediately report any symptoms of dehydration.

Most healthy people can treat mild cases of dehydration on their own by eating food and drinking adequate amounts of water. However, symptoms that worsen or do not improve should be reported to a physician. Anyone believed to have moderate to severe dehydration should seek immediate medical attention.

Treatment for dehydration includes replacing fluids that have been lost. In mild cases, this usually involves drinking more water. Eating foods high in water content (such as certain fruits and vegetables) may also be advised. Other fluids used to treat mild dehydration include:

• Oral rehydration solution. Fluids specially formulated to replace water and electrolyte imbalances, especially when dehydration is due to vomiting and/or diarrhea. These solutions are available over the counter at pharmacies and grocery stores.
  
  
• Sports drinks. These commercial products are available for over-the-counter purchase at most stores. They provide fluids, electrolytes and carbohydrates. These drinks may contain more sugar and less electrolytes than oral rehydration solutions.

Dehydration may be prevented by maintaining adequate water balance in the body. This involves drinking regularly, before thirst develops. People can often carry a bottle of water with them throughout the day for easy access to fluids. A general rule of thumb for determining baseline daily fluid needs is to multiply the person's body weight in kilograms by 30 milliliters (ml). 

Prevention also depends on becoming aware of circumstances that put people at greater risk of dehydration. When such circumstances are foreseen, prehydration can be helpful. Prehydration means taking in additional fluids prior to anticipated fluid loss. For instance, breastfeeding mothers often drink additional fluids before a scheduled feeding. Or, people can drink several glasses of water prior to gardening on a hot day.

Additional dehydration prevention methods include:

• Drink cool or cold liquids (e.g., water, sports drinks) before, during and after play, sports or any type of physical exertion. Cold fluids are more efficiently absorbed than warm fluids. They also play a part in cooling body temperature, helping to avoid complications such as heat exhaustion and heat stroke. Drinking should occur every 20 minutes during exercise. The amount consumed may depend on a person’s size, for example:

Body Weight	Amount of Fluid Intake (every 20 minutes)
Less than 88 pounds (40 kilograms)	5 ounces (148 milliliters)
88 to 132 pounds (40 to 60 kilograms)	9 ounces (266 milliliters)
More than 132 pounds (60 kilograms)	10 to 12 ounces (296 to 355 milliliters)

• Take steps to prevent overheating. This may include taking breaks every 20 to 30 minutes during sports or other vigorous activity, as well as periodically stepping out of the heat or humidity into a shaded or cool location. Outdoor sports should be performed in early mornings or late afternoons to avoid physical exertion during the hottest times of the day.
  
  
• Limit intake of sodium, caffeine and alcohol. Foods and beverages containing high amounts of salt can draw water out of body cells to dilute high levels of salt in the mouth and gastrointestinal tract. The more sodium that is ingested, the higher the risk of mild dehydration. Caffeine has a diuretic effect, increasing urination above normal levels and contributing to the loss of excess fluids from the body. Alcohol interferes with the body’s ability to absorb water through the gastrointestinal tract.
  
  
• Know what to do in extreme survival conditions. People who participate in hiking or other outdoor activities (e.g., mountain climbing, rock climbing) should be prepared with additional stores of fluids in case they get lost or are stranded. It is important to remain as hydrated as possible until help arrives.

Because certain medications may increase the risk of dehydration (e.g., diuretics, chemotherapy), patients should consult their physician about the best way to prevent dehydration. A physician may encourage drinking extra water with the medication, or prescribe antiemetics (anti-nausea medications) to reduce the likelihood of fluid loss from vomiting.

People with a high risk of dehydration (e.g., infants, children, the elderly) may need extra hydration prior to a medical procedure requiring that foods and liquids be restricted. Anyone concerned about loss of fluids prior to such a procedure should consult their physician. The use of intravenous (I.V.) fluids may be recommended before, during and after the procedure to ensure adequate hydration.

Salt pills are not advised as they can cause hypernatremia (dehydration caused by excess sodium in the body). In the past, salt pills were recommended for use during sports activities in hot weather to help prevent dehydration. However, they are not used much today.

Preparing questions in advance can help patients have more meaningful discussions with health professionals about their conditions. Patients may wish to ask their doctor the following questions related to dehydration:

1. Do any of my conditions or activities put me at an increased risk of dehydration?
   
   
2. What signs or symptoms may indicate dehydration?
   
   
3. What should I do if I become dehydrated? At what point should I call you or seek immediate medical attention?
   
   
4. What type of fluids (e.g., water, sports drinks, oral rehydration solutions) do you recommend? Are there certain brands you recommend?
   
   
5. How can I stay hydrated if I’m repeatedly vomiting?
   
   
6. Are there certain foods or beverages I should avoid if I’m dehydrated?
   
   
7. How can I prevent dehydration?
   
   
8. What amount of fluids should I drink every day?
   
   
9. If I’m pregnant or breastfeeding, how much extra fluid should I drink?
   
   
10. How can I help the person I’m caring for (e.g., infant, child, elder) drink more fluids?