Dehydration occurs when your body loses more fluid than you take in.
When the normal water content of your body is reduced, it upsets the balance of minerals (salts and sugar) in your body, which affects the way that it functions.
Water makes up over two-thirds of the healthy human body. It lubricates the joints and eyes, aids digestion, flushes out waste and toxins and keeps the skin healthy.
Some of the early warning signs of dehydration include:
- feeling thirsty and lightheaded
- having dark coloured, strong-smelling urine
- passing urine less often than usual
A baby may be dehydrated if they:
- have a sunken soft spot (fontanelle) on their head
- have few or no tears when they cry
- have fewer wet nappies
- are drowsy
The body is affected even when you lose a small amount of fluid.
Read more about the symptoms of dehydration.
What causes dehydration?
Dehydration is usually caused by not drinking enough fluid or by fluid that is lost and not replaced. The climate, the amount of physical exercise you are doing and your diet can also contribute to dehydration.
You can also become dehydrated as a result of an illness, such as persistent vomiting and diarrhoea or sweating from a fever, or exercising in hot conditions.
Read more about the causes of dehydration.
Who is at risk from dehydration?
Anyone can become dehydrated, but certain groups are particularly at risk. These include:
- babies and infants – they have a low body weight and are sensitive to even small amounts of fluid loss
- older people – they may be less aware that they are becoming dehydrated and need to keep drinking fluids
- people with a long-term health condition – such as diabetes or alcoholism
- athletes – they lose a large amount of body fluid through sweat
What to do
Drink plenty of fluids if you're dehydrated. This can be water, semi-skimmed milk, diluted squash or fruit juice, but it's best to avoid caffeine and fizzy drinks.
If you're finding it difficult to keep water down because you're vomiting or have diarrhoea, try drinking small amounts more frequently.
Infants and children who are dehydrated shouldn't be given water as the main replacement fluid because it can dilute the already low level of minerals in their body and make the problem worse.
Instead, they should be given diluted squash, diluted fruit juice or a rehydration solution (available from pharmacies). You might find a teaspoon or syringe can be helpful for getting fluid into a young child.
If left untreated, severe dehydration can be serious and cause fits (seizures), brain damage and death.
Read more about treating dehydration.
When to see your GP
See your GP if your symptoms continue, despite drinking plenty of fluids, or if you suspect that your baby or toddler is dehydrated.
If your GP suspects dehydration, you may have a blood test or a urine test to check the balance of salts (sodium and potassium) in your body.
Contact your GP or out-of-hours service straight away if you have any of the following symptoms:
- feeling tired (lethargic) or confused
- dry mouth and eyes that don't produce tears
- not passing urine for eight hours
- dry skin that sags slowly into position when pinched up
- rapid heartbeat
- blood in your stools (faeces) or vomit
- low blood pressure (hypotension)
You should also contact your GP if your baby has passed six or more diarrhoeal stools in the past 24 hours, or if they have vomited three times or more in the past 24 hours.