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 replace lost fluids, you will get dehydrated.
Anyone may become dehydrated, but the condition is especially dangerous for young children and older adults.
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. Keep an eye on how much fluid you lose during hot weather, illness or exercise, and drink enough liquids to replace what you’ve lost.
- 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.
Thirst isn’t always a reliable early indicator of the body’s need for water. Many people, particularly older adults, don’t feel thirsty until they’re already dehydrated. That’s why it’s important to increase water intake during hot weather or when you’re ill.
The signs and symptoms of dehydration also may differ by age.
Infant or young child
- Dry mouth and tongue
- No tears when crying
- No wet diapers for three hours
- Sunken eyes, cheeks
- Sunken soft spot on top of skull
- Listlessness or irritability
- Extreme thirst
- Less frequent urination
- Dark-colored urine
When to see a doctor
- Has had diarrhea for 24 hours or more
- Is irritable or disoriented and much sleepier or less active than usual
- Can’t keep down fluids
- Has bloody or black stool
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.
- In general, the higher your fever, the more dehydrated you may become. The problem worsens if you have a fever in addition to diarrhea and vomiting.
- 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.
- Increased urination.This may be due to undiagnosed or uncontrolled diabetes. Certain medications, such as diuretics and some blood pressure medications, also can lead to dehydration, generally because they cause you to urinate more.
To prevent dehydration, drink plenty of fluids and eat foods high in water such as fruits and vegetables. Letting thirst be your guide is an adequate daily guideline for most healthy people.
People may need to take in more fluids if they are experiencing conditions such as:
- Vomiting or diarrhea.If your child is vomiting or has diarrhea, start giving extra water or an oral rehydration solution at the first signs of illness. Don’t wait until dehydration occurs.
- Strenuous exercise.In general, it’s best to start hydrating the day before strenuous exercise. Producing lots of clear, dilute urine is a good indication that you’re well-hydrated. During the activity, replenish fluids at regular intervals and continue drinking water or other fluids after you’re finished.
- Hot or cold weather.You need to drink additional water in hot or humid weather to help lower your body temperature and to replace what you lose through sweating. You may also need extra water in cold weather to combat moisture loss from dry air, particularly at higher altitudes
- Older adults most commonly become dehydrated during minor illnesses — such as influenza, bronchitis or bladder infections. Make sure to drink extra fluids when you’re not feeling well.
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.
For infants and children who have become dehydrated from diarrhea, vomiting or fever, use an over-the-counter oral rehydration solution. These solutions contain water and salts in specific proportions to replenish both fluids and electrolytes.
Most adults with mild to moderate dehydration from diarrhoea, vomiting or fever can improve their condition by drinking more water or other liquids. Diarrhoea may be worsened by full-strength fruit juice and soft drinks.
If you work or exercise outdoors during hot or humid weather, cool water is your best bet. Sports drinks containing electrolytes and a carbohydrate solution also may be helpful.
Children and adults who are severely dehydrated should be treated by emergency personnel arriving in an ambulance or in a hospital emergency room.