Dehydration
This article is general health information for the selected condition. It is not a diagnosis and does not replace clinical judgement. If you have questions or need treatment advice, please consult a qualified healthcare professional.
What is dehydration?
Dehydration occurs when fluid loss exceeds intake, reducing the water available for normal body function. It ranges from mild thirst to a life threatening emergency, and it is most dangerous at the extremes of age. In older adults thirst is blunted, so confusion or a fall may be the first sign rather than any complaint of thirst.
Causes
- Vomiting and diarrhoea
- Fever and excessive sweating
- Inadequate fluid intake
- Uncontrolled diabetes causing high urine output
- Diuretic medicines
- Burns and significant blood loss
- Heat exposure and strenuous exercise
Symptoms
- Thirst and dry mouth
- Dark concentrated urine and reduced output
- Fatigue and light headedness
- Headache
- Dizziness on standing
- Reduced skin elasticity
- Sunken eyes and, in infants, a sunken fontanelle
- Confusion, rapid pulse and low blood pressure when severe
Risk factors
- Infants and young children
- Older adults with reduced thirst sensation
- Chronic illness including diabetes and kidney disease
- Diuretic or laxative use
- Hot climates and outdoor work
- Limited mobility or dependence on carers for drinks
Diagnosis
- Clinical assessment of pulse, blood pressure and capillary refill
- Postural blood pressure measurement
- Urine output and colour
- Blood tests for urea, creatinine and electrolytes
- Weight change in children as a guide to fluid deficit
Treatment
- Oral rehydration solution, which is preferable to water alone in illness
- Small frequent sips when vomiting
- Intravenous fluids for severe dehydration or inability to drink
- Treating the underlying cause
- Careful correction of sodium abnormalities
- Prevention through scheduled drinks in at risk groups
Self care
- Use oral rehydration solution rather than water alone during illness
- Sip small amounts frequently if vomiting
- Continue breastfeeding or formula in infants
- Return to normal eating as soon as tolerated
- Avoid sugary drinks, which can worsen diarrhoea
- Watch urine colour as a simple guide
- Offer drinks proactively to older adults who may not feel thirsty
When to see a doctor
Book an appointment if:
- Diarrhoea or vomiting lasting more than two days
- Unable to keep fluids down
- Dark urine or reduced output despite drinking
- Dizziness on standing
- Dehydration in an infant, older adult or someone with kidney disease
- Diabetes with vomiting, which risks ketoacidosis
Some symptoms need emergency care rather than an appointment. See the warning signs listed above.
Prevention
- Drink regularly in hot weather and during exercise
- Keep oral rehydration sachets at home
- Increase fluids at the first sign of vomiting or diarrhoea
- Prompt older adults and children to drink through the day
- Adjust diuretic doses during illness on medical advice
Outlook
Mild to moderate dehydration corrects quickly and completely with oral rehydration. Severe dehydration is a medical emergency but responds well to intravenous fluids. Repeated or prolonged severe episodes can injure the kidneys, which is why early rehydration matters most in infants, older adults and people with existing kidney disease.
Common questions
When does dehydration need emergency care?
Confusion or marked drowsiness, inability to keep any fluid down, no urine for eight hours or more, a rapid weak pulse, fainting, or a sunken fontanelle in a baby all need urgent medical attention.
Why is oral rehydration solution better than water?
It contains a balance of glucose and salts that uses the intestine sodium glucose transporter to absorb water efficiently, and it replaces the electrolytes lost through vomiting and diarrhoea.
Are sports drinks a good substitute?
They are designed for exercise and generally contain too much sugar and too little sodium for illness related dehydration. Proper oral rehydration solution is preferable when there is vomiting or diarrhoea.
References
Important: Dard AI is not a medical device and does not diagnose, treat, or replace clinician judgement. This article is general information only. Always consult a qualified healthcare professional about diagnosis and treatment, and seek emergency care for severe or rapidly worsening symptoms.