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What Is Dehydration?
Dehydration happens when your body loses more fluid than you take in. Water supports circulation, temperature control, digestion, and normal organ function, while electrolytes help regulate fluids, nerves, and muscles. Infants, children, older adults, and people with illnesses that cause vomiting, diarrhea, fever, or increased urination are at higher risk. Dehydration can also affect blood pressure, especially when fluid loss is significant.
Symptoms
Symptoms of Dehydration
- Thirst
- Dry mouth
- Dark urine
- Urinating less often
- Fatigue
- Dizziness
- Headache
- Nausea
- Muscle cramps
Age-Specific Signs Caregivers May Notice
- Fewer wet diapers
- No tears when crying
- Unusual sleepiness
- Irritability
- Confusion
- Difficulty drinking
Causes
Causes of Dehydration
Dehydration occurs when fluid loss is greater than fluid intake. The body may lose water and electrolytes through the digestive tract, urine, sweat, skin, or breathing, or a person may be unable to drink enough to replace those losses.
- Vomiting can rapidly remove fluids and electrolytes from the body.
- Diarrhea can cause substantial fluid and electrolyte loss, especially when it is frequent.
- Fever can increase fluid loss through sweating and faster breathing.
- Heavy sweating during exercise or illness can reduce the body’s fluid volume.
- Hot-weather exposure can increase sweating and make dehydration more likely.
- Frequent urination can cause fluid loss, including when related to diabetes or certain medicines.
- Burns can cause fluid to move out of the bloodstream through damaged skin.
- Inability to access, swallow, or safely drink fluids can lead to inadequate intake.
- Medicines or medical conditions that increase fluid loss can contribute to dehydration.
Risk Factors
Risk Factors for Dehydration
| Higher-risk group | Why risk is higher | What to monitor |
|---|---|---|
| Babies and young children | They lose fluid quickly and depend on adults for fluids. | Wet diapers, tears, drinking, and alertness |
| Older adults | Thirst may be reduced and mobility or memory problems may limit intake. | Urination, confusion, weakness, and fluid intake |
| People with vomiting or diarrhea | Fluid and electrolytes may be lost faster than they are replaced. | Ability to keep fluids down and urine output |
| People exercising or working in heat | Sweating increases fluid loss. | Thirst, dizziness, cramps, and heat-related symptoms |
- Pregnancy can increase fluid needs and the effects of fluid loss.
- Breastfeeding increases fluid needs because fluid is used to make milk.
- Fever can increase fluid loss and make replacement more important.
- Diabetes can increase urination and fluid loss when blood glucose is high.
- Kidney disease can affect the body’s ability to balance fluids.
- Diuretics, sometimes called water pills, can increase urination; this factor is modifiable only with medical guidance.
- Limited access to safe drinking water is a preventable environmental risk when reliable fluids can be arranged.
Complications
Complications of Dehydration
As fluid and electrolyte loss worsens, the circulating blood volume may fall. This can affect blood pressure, temperature regulation, kidney function, and brain function, causing the severe effects of dehydration.
- Electrolyte imbalance can interfere with nerve, muscle, and heart function.
- Heat injury can occur when dehydration limits the body’s ability to cool itself.
- Kidney injury can develop when the kidneys receive too little blood flow.
- Low blood pressure can occur when fluid loss reduces circulating blood volume.
- Shock can develop when severe fluid loss prevents organs from receiving enough blood and oxygen.
- Seizures may occur when severe electrolyte changes or reduced brain function affect the nervous system.
- Loss of consciousness can result from severely reduced blood flow to the brain.
Diagnosis
How Dehydration Is Diagnosed
Clinicians ask about fluid intake, vomiting, diarrhea, sweating, urination, medicines, and medical conditions. They check vital signs and physical findings such as mouth moisture, alertness, skin changes, and urine output. The assessment helps determine how severe the fluid loss is and what caused it.
- Blood tests may measure electrolytes and kidney function.
- Urine testing may provide information about fluid concentration and kidney function.
- Tests directed at the suspected cause may be recommended, such as testing for an infection or evaluating ongoing vomiting or diarrhea.
- The need for testing depends on the severity of symptoms and the person’s age and overall health.
Treatment & Management
Dehydration Treatment and Management
Mild dehydration is often treated by taking frequent small sips of water or an appropriate oral rehydration solution. Treatment should also address the cause, such as vomiting, diarrhea, fever, heat exposure, or another illness. People who cannot replace fluids safely or who have severe symptoms may need medical treatment.
| Approach | When it may be used | What it involves |
|---|---|---|
| Small frequent sips | Mild symptoms and ability to drink | Water or an appropriate oral rehydration solution taken gradually |
| Medical assessment | Ongoing losses, higher-risk patients, or inability to replace fluids | Evaluation, treatment of the cause, and monitoring of electrolytes or kidney function |
| Intravenous fluids | Severe dehydration or inability to drink safely | Fluids and electrolytes delivered through a vein under medical supervision |
Prevention
How to Prevent Dehydration
- Drink fluids regularly rather than waiting until you are very thirsty.
- Increase fluids during hot weather, exercise, or other activities that cause sweating.
- Replace fluid losses during vomiting or diarrhea with an appropriate oral rehydration solution.
- Monitor urine and wet diapers for changes that may suggest fluid loss.
- Keep safe drinking water or other suitable fluids accessible at home, work, and during travel.
- Ask a clinician about fluid limits if you have heart disease or kidney disease.
Fluid needs vary by age, activity level, climate, pregnancy, breastfeeding, illness, and medical conditions. People with ongoing health problems should follow individualized advice rather than changing fluid intake on their own. Dehydration symptoms in women and men may be similar, but pregnancy and breastfeeding can change fluid needs.
Outlook and Prognosis
Outlook and Prognosis for Dehydration
Mild dehydration often improves after the cause is corrected and fluids are replaced. Severe or prolonged dehydration may require hospital treatment and can cause lasting complications involving the kidneys, brain, or other organs. Recovery depends on the amount of fluid lost, the underlying cause, the person’s age and health, and how quickly treatment begins.
When Should You See a Doctor
When Should You See a Doctor for Dehydration?
Get medical help
Know when dehydration is an emergency
Contact a clinician urgently for signs of significant fluid loss or when fluids cannot be replaced. Call emergency services for collapse, unresponsiveness, a seizure, or signs of shock.
- Very little or no urine
- Confusion
- Fainting
- Severe weakness
- Rapid breathing
- Severe dizziness
- Blood in vomit or stool
- Persistent vomiting or diarrhea
- Inability to keep fluids down
- Collapse or unresponsiveness
- Seizure
- Signs of shock
Seek advice promptly for babies, older adults, pregnant people, people with kidney or heart disease, and anyone taking medicines that affect fluid balance. Medical guidance is also important when symptoms worsen, recur, or do not improve with careful fluid replacement.
