Overview
Dehydration means the body has lost more fluid than it has taken in, so there is not enough left for it to work properly. Salts such as sodium and potassium are lost along with the water, which is why replacing both matters.
Mild dehydration is common and easily corrected at home. It becomes dangerous when losses are fast, as in heavy diarrhoea, or when the person cannot drink, and babies, small children and older people reach that point sooner than healthy adults.
Symptoms
In adults and older children:
- Thirst and a dry mouth, lips and tongue
- Dark yellow, strong-smelling urine, and passing urine less often
- Headache, dizziness or light-headedness, especially on standing
- Tiredness and weakness
- Sunken eyes
In babies and young children:
- A sunken soft spot on the top of the head
- Sunken eyes, and few or no tears when crying
- Fewer wet nappies than usual
- Being drowsy, floppy, restless or irritable
- Drinking eagerly and thirstily, or in severe cases being unable to drink
- Skin that goes back slowly when it is pinched
Older people may not feel thirsty at all, and dehydration can show first as confusion, a sudden loss of strength or a fall.
When to see a doctor
See a doctor within a day or two for dark urine and unusual tiredness, for dizziness on standing, for diarrhoea or vomiting lasting more than two days, and sooner for a baby, an older person or anyone with diabetes or kidney disease.
Causes
The commonest cause is diarrhoea, with or without vomiting, which takes out water and electrolytes through the stools. Fever, heavy sweating in the heat and hard physical work add to the losses.
Dehydration also follows poorly controlled diabetes, which makes the body pass large amounts of urine, water tablets and some other medicines, alcohol, and simply not drinking enough, which is easy when someone is unwell, busy or dependent on others for a glass of water.
Risk factors
- Babies and young children, who lose fluid quickly and cannot ask for a drink
- Older people, whose sense of thirst is blunted
- Diabetes, kidney disease and other long-term illnesses
- Water tablets and some medicines
- Outdoor work and sport in hot weather
- Unsafe drinking water and poor sanitation, which cause repeated diarrhoea
- Anyone being sick, feverish or unable to swallow comfortably
Complications
As dehydration deepens, the falls and the circulation begins to fail, which is called shock. The kidneys can be injured by the low flow of blood through them, and disturbed salt levels can cause weakness, confusion or a fit.
Dehydration also makes heat illness more likely, and in small children it remains one of the main reasons that a diarrhoeal illness becomes life-threatening.
Prevention
- Drink through the day rather than waiting for thirst, and more in hot weather or during illness
- Start as soon as diarrhoea or vomiting begins, rather than waiting for signs of dehydration
- Keep ORS sachets at home, and check the expiry date
- Use safe drinking water, wash hands with soap, and keep food covered
- Continue breastfeeding and feeding a child through a diarrhoeal illness
- Offer drinks regularly to older relatives and to anyone who cannot fetch their own
- Take extra fluid before, during and after outdoor work or exercise in the heat
Diagnosis
Dehydration is judged mostly at the bedside: how alert the person is, whether the eyes look sunken, how eagerly they drink, the pulse and , how much urine is being passed, and how slowly pinched skin returns.
Blood tests for the salts, kidney function and sugar, and a urine test, are used when the dehydration is more than mild or when the cause is not clear. A stool test may be added if the diarrhoea is bloody or prolonged.
Treatment
Most dehydration is treated by drinking. Take small sips often rather than large amounts at once, which is easier to keep down, and carry on for as long as the losses continue.
- Mix one whole sachet of oral rehydration salts into the exact volume of clean water printed on it, and use it within the time the packet states
- Give a child a few spoonfuls every few minutes, and give more after each loose stool or vomit
- Carry on breastfeeding or feeding as usual alongside the ORS
- Children with diarrhoea are also given zinc, which shortens the illness
- Avoid alcohol and drinks with a lot of caffeine while rehydrating
Severe dehydration, or an inability to keep fluids down, is treated in hospital with fluids and salts given into a vein, with monitoring of the salts and the kidneys. The underlying cause is treated too, whether that is an infection, uncontrolled diabetes or a medicine that needs adjusting.
Myths and facts
Things people often say about this. Open each one to see what is true.
Myth“Stop giving a child with diarrhoea anything to drink, so the loose motions stop.”What is true?
Fact
This is the opposite of what is needed, and it is dangerous. The threat in diarrhoea is dehydration, not the stools themselves. The World Health Organization treatment is oral rehydration solution given throughout the illness, with zinc for children, and feeding and breastfeeding continued.
Myth“Plain water is enough, so there is no point in an ORS packet.”What is true?
Fact
Diarrhoea and vomiting take out salts as well as water, and plain water does not replace them. Oral rehydration solution is made of clean water, salt and sugar in the right proportions, which is why it works. Mix the whole sachet into the amount of water written on it, neither stronger nor weaker.
Myth“A cup of tea, a coffee or a cold beer will rehydrate you in the heat.”What is true?
Fact
Alcohol makes dehydration worse, and health guidance is to avoid both alcohol and caffeine while rehydrating. Water, oral rehydration solution, milk or diluted juice are better choices when fluid has been lost.
Myth“Old people do not need to drink unless they feel thirsty.”What is true?
Fact
The sense of thirst weakens with age, so an older person can be quite dehydrated and still not feel thirsty. Confusion, sudden weakness, a fall or dark urine may be the first sign. Regular drinks through the day, offered rather than waited for, are the safer habit.
Questions to ask your doctor
Tick the ones you want answered and take them with you.
Common questions
Can I make oral rehydration solution at home?
A ready-made ORS sachet is the reliable option, because the balance of salt and sugar is already correct, and the packets are cheap and widely available. A home-made salt and sugar drink is a stop-gap only, and getting the proportions wrong can do harm, so ask a doctor or pharmacist exactly how to make it if no sachet is available.
My child keeps vomiting the ORS back up. What should I do?
Give very small amounts very often, a teaspoon every minute or two, rather than a cupful at a time, and wait a few minutes after a vomit before starting again. If nothing at all stays down, or the child becomes drowsy, has sunken eyes or is passing very little urine, take them to hospital.
Does dark urine always mean dehydration?
Not always. Some vitamins, medicines and foods colour the urine, and liver problems can darken it too. But dark, strong-smelling urine with a dry mouth, tiredness and passing urine less often is a good practical sign of dehydration, and it is worth acting on.