Dehydration occurs when you lose more fluid than you take in, and your body doesn’t have enough water and other fluids to carry out its normal functions. If you don’t replenish lost fluids, you may suffer serious consequences.
Common causes of dehydration include intense diarrhea, vomiting, fever or excessive sweating. Inadequate intake of water during hot weather or exercise also may cause dehydration. Anyone may become dehydrated, but young children, older adults and people with chronic illnesses are most at risk.
Mild to moderate dehydration is likely to cause:
- Dry, sticky mouth
- Sleepiness or tiredness — children are likely to be less active than usual
- Decreased urine output — fewer than six wet diapers a day for infants and eight hours or more without urination for older children and teens
- Few or no tears when crying
- Muscle weakness
- Dizziness or lightheadedness
Severe dehydration, a medical emergency, can cause:
- Extreme thirst
- Extreme fussiness or sleepiness in infants and children; irritability and confusion in adults
- Very dry mouth, skin and mucous membranes
- Lack of sweating
- Little or no urination — any urine that is produced will be dark yellow or amber
- Sunken eyes
- Shriveled and dry skin that lacks elasticity and doesn’t “bounce back” when pinched into a fold
- In infants, sunken fontanels — the soft spots on the top of a baby’s head
- Low blood pressure
- Rapid heartbeat
- In the most serious cases, delirium or unconsciousness
Unfortunately, thirst isn’t always a reliable gauge of the body’s need for water, especially in children and older adults. A better barometer is the color of your urine: Clear or light-colored urine means you’re well hydrated, whereas a dark yellow or amber color usually signals dehydration.
If you’re an average adult, every day you lose more than 10 cups (close to 2.5 liters) of water simply by sweating, breathing and eliminating waste. You also lose electrolytes — minerals such as sodium, potassium and calcium that maintain the balance of fluids in your body. Normally, you can replenish what you’ve lost through the foods and liquids you consume, even when you’re active.
But when you eliminate more water and salts than you replace, dehydration results — your system literally dries out. Sometimes dehydration occurs for simple reasons: You don’t drink enough because you’re sick or busy, or because you lack access to potable water when you’re traveling, hiking or camping.
Other dehydration causes include:
- Diarrhea, vomiting. Severe, acute diarrhea — that is, diarrhea that comes on suddenly and violently — can cause a tremendous loss of water and electrolytes in a short amount of time. If you have vomiting along with diarrhea, you lose even more fluids and minerals. Children and infants are especially at risk. Dehydration is a leading cause of death in children worldwide. In the United States, up to 300 children die of dehydration each year.
- Fever. In general, the higher your fever, the more dehydrated you may become. If you have a fever in addition to diarrhea and vomiting, you lose even more fluids.
- Excessive sweating. You lose water when you sweat. If you engage in vigorous activity and don’t replace fluids as you go along, you can become dehydrated. Hot, humid weather increases the amount you sweat and the amount of fluid you lose. But you can also become dehydrated in winter if you don’t replace lost fluids. Preteens and teens who participate in sports may be especially susceptible, both because of their body weight, which is generally lower than that of adults, and because they may not be experienced enough to know the warning signs of dehydration.
- Increased urination. This is most often the result of undiagnosed or uncontrolled diabetes mellitus, a disease that affects the way your body uses blood sugar and that often causes increased thirst and more frequent urination. Another type of diabetes, diabetes insipidus, also is characterized by excessive thirst and urination, but in this case the cause is a hormonal disorder that makes your kidneys unable to conserve water. Certain medications — diuretics, antihistamines, blood pressure medications and some psychiatric drugs — as well as alcohol also can lead to dehydration, generally because they cause you to urinate or perspire more than normal.
- Burns. Doctors classify burns according to the depth of the injury and the extent of tissue damage. Third-degree burns are the most severe, penetrating all three layers of skin, and often destroying sweat glands, hair follicles and nerve endings. People with third-degree burns or extensive first- or second-degree burns experience profound fluid loss, and the resulting dehydration can be life-threatening.
Anyone can become dehydrated if the loss of fluids outweighs fluid intake. But certain people are at greater risk, including:
- Infants and children. Worldwide, dehydration caused by diarrhea is a leading cause of death in children. Infants and children are especially vulnerable because of their relatively small body weights and high turnover of water and electrolytes. They’re also the group most likely to experience diarrhea. In the United States, diarrhea remains one of the most common childhood illnesses.
- Older adults. As you age, you become more susceptible to dehydration for several reasons: Your body’s ability to conserve water is reduced, your thirst sense becomes less acute and you’re less able to respond to changes in temperature. What’s more, older adults, especially people in nursing homes or living alone, tend to eat less than younger people do and sometimes may forget to eat or drink altogether. Disability or neglect also may prevent them from being well nourished. These problems are compounded by chronic illnesses such as diabetes, by hormonal changes associated with menopause and by the use of certain medications.
- People with chronic illnesses. Having uncontrolled or untreated diabetes puts you at high risk of dehydration. But other chronic illnesses also make you more likely to become dehydrated. These include kidney disease, cystic fibrosis, alcoholism and adrenal gland disorders. Even having a cold or sore throat makes you more susceptible to dehydration because you’re less likely to feel like eating or drinking when you’re sick. A fever increases dehydration even more.
- Endurance athletes. Anyone who exercises can become dehydrated, especially in hot, humid conditions or at high altitudes. But athletes who train for and participate in ultramarathons, triathlons, mountain climbing expeditions and cycling tournaments are at particularly high risk. That’s because the longer you exercise, the more difficult it is to stay hydrated. During exercise, your body can absorb about 24 to 32 ounces of water an hour, but you may lose twice that amount in hot weather. With every hour, your fluid debt increases. Dehydration is also cumulative over a period of days, which means you can become dehydrated with even a moderate exercise routine if you don’t drink enough to replace what you lose on a daily basis.
- People living at high altitudes. Living, working and exercising at high altitudes (generally defined as 8,000 to 12,000 feet, or about 2,400 to 3,600 meters) or very high altitudes (12,000 to 18,000 feet, or about 3,600 to 5,400 meters) can cause a number of health problems. One is dehydration, which commonly occurs when your body tries to adjust to high elevations through increased urination and more rapid breathing — the faster you breathe to maintain adequate oxygen levels in your blood, the more water vapor you exhale.
Dehydration can lead to serious complications, including:
- Heat injury. Inadequate fluid intake combined with vigorous exercise and heavy perspiration can lead to heat injury, ranging in severity from mild heat cramps to heat exhaustion to potentially life-threatening heatstroke.
- Swelling of the brain (cerebral edema). Most often, the fluid you lose when you’re dehydrated contains the same amount of sodium your blood does (isotonic dehydration). In some instances, though, you may lose more sodium than fluid (hypotonic dehydration). To compensate for this loss, your body produces particles that pull water back into the cells. As a result, your cells may absorb too much water during the rehydration process, causing them to swell and rupture. The consequences are especially grave when brain cells are affected.
- Seizures. These occur when the normal electrical discharges in your brain become disorganized, leading to involuntary muscle contractions and sometimes to a loss of consciousness.
- Hypovolemic shock. This is one of the most serious complications of dehydration. It occurs when low blood volume causes a drop in blood pressure and a corresponding reduction in the amount of oxygen reaching your tissues. If untreated, severe hypovolemic shock can cause death in a matter of minutes.
- Kidney failure. This potentially life-threatening problem occurs when your kidneys are no longer able to remove excess fluids and waste from your blood.
- Coma and death. When not treated promptly and appropriately, severe dehydration can be fatal.
Your doctor can often diagnose dehydration on the basis of physical signs and symptoms such as little or no urination, sunken eyes, and skin that lacks its normal elasticity and resilience when pinched. If you’re dehydrated, you’re also likely to have low blood pressure, especially when moving from a prone to a standing position, a faster than normal heart rate and reduced blood flow to your extremities.
To help confirm the diagnosis and pinpoint the degree of dehydration, you may have other tests, such as:
- Blood tests. These may be used to check your electrolytes, especially sodium and potassium; to look for signs of concentrated blood; and to evaluate how well your kidneys are working.
- Urinalysis. The color and clarity of your urine, the presence of carbon compounds (ketones) and your urine’s specific gravity — that is, the mass of the urine as compared with equal amounts of distilled water — all help show whether you’re dehydrated and to what degree. A high specific gravity, for example, indicates significant dehydration.
The only effective treatment for dehydration is to replace lost fluids and lost electrolytes. The best approach to dehydration treatment depends on your age, the severity of your dehydration and its cause.
Most adults with mild to moderate dehydration from diarrhea, vomiting or fever can improve their condition by drinking more water. Water is best because other liquids, such as fruit juices, carbonated beverages or coffee, can make diarrhea worse. Children and adults who are severely dehydrated should be treated by emergency personnel arriving in an ambulance or in a hospital emergency room, where they can receive salts and fluids through a vein (intravenously) rather than by mouth. Intravenous hydration provides the body with water and essential nutrients much more quickly than oral solutions do — something that’s essential in life-threatening situations.
To prevent dehydration, consume plenty of fluids and foods high in water such as fruits and vegetables.