Dehydration occurs when you use or 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 replace lost fluids, you will get dehydrated.
Common causes of dehydration include vigorous exercise, especially in hot weather; intense diarrhea; vomiting; fever or excessive sweating. Not drinking enough water during exercise or in hot weather even if you're not exercising also may cause dehydration. Anyone may become dehydrated, but young children, older adults and people with chronic illnesses are most at risk.
You can usually reverse mild to moderate dehydration by drinking more fluids, but severe dehydration needs immediate medical treatment. The safest approach is preventing dehydration in the first place. Drink enough liquids to replace what you've lost.
Mild to moderate dehydration is likely to cause:
- Dry, sticky mouth
- Sleepiness or tiredness
- Decreased urine output
- Dry skin
- Dizziness or lightheadedness
Severe dehydration, a medical emergency, can cause:
- Extreme thirst
- Dry, cracked toungue
- Little or no urination — any urine that is produced will be darker than normal
- Sunken eyes
- Shriveled and dry skin that lacks elasticity and doesn't "bounce back" when pinched into a fold
- Low blood pressure
- Rapid heartbeat
- Rapid breathing
- 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 indicator 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.
When to see a doctor
Get immediate medical care if you develop severe signs and symptoms of dehydration.
Dehydration occurs when there isn't enough water to replace what's lost throughout the day. 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 safe drinking 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.
- 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 do 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 may be due to undiagnosed or uncontrolled diabetes.
Dehydration can lead to serious complications, including:
- Heat injury. If you don't drink enough fluids when you're exercising vigorously and perspiring heavily, you may end up with a heat injury, ranging in severity from mild heat cramps to heat exhaustion or potentially life-threatening heatstroke.
- Swelling of the brain (cerebral edema). Sometimes, when you're getting fluids again after being dehydrated, the body tries to pull too much water back into your cells. This can cause some cells to swell and rupture. The consequences are especially grave when brain cells are affected.
- Seizures. Electrolytes — such as potassium and sodium — help carry electrical signals from cell to cell. If your electrolytes are out of balance, the normal electrical messages can become mixed up, which can lead to involuntary muscle contractions and sometimes to a loss of consciousness.
- Low blood volume shock (hypovolemic shock). This is one of the most serious, and sometimes life-threatening, complications of dehydration. It occurs when low blood volume causes a drop in blood pressure and a drop in the amount of oxygen in your body.
- 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 lying 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. Blood samples may be used to check for a number of factors, such as the levels of your electrolytes — especially sodium and potassium — and how well your kidneys are working.
- Urinalysis. Tests done on your urine can help show whether you're dehydrated and to what degree.
If it's not obvious why you're dehydrated, your doctor may order additional tests to check for diabetes and for liver or kidney problems.
The only effective treatment for dehydration is to replace lost fluids and lost electrolytes. The best approach to dehydration treatment depends on age, the severity of dehydration and its cause.
Most people with mild to moderate dehydration from diarrhea, vomiting or fever can improve their condition by drinking electrolyte solutions such as Gatorade, Powerade or Pedialyte. Certain liquids, such as fruit juices, carbonated beverages or coffee, can make diarrhea worse.