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 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
- a dry mouth
- 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 (nappies will feel lighter)
- are drowsy
The body is affected even when you lose a small amount of fluid.
What causes dehydration?
Dehydration is usually caused by not drinking enough fluid to replace what we lose. The climate, the amount of physical exercise you are doing (particularly in hot weather) and your diet can 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.
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 can lose a large amount of body fluid through sweat when exercising for long periods
What to do
If you’re at risk of dehydration, drink plenty of fluids such as water or diluted squash. These are much more effective than large amounts of tea, coffee or fizzy drinks, which contain caffeine.
If you’re finding it difficult to keep water down because you’re vomiting, try drinking small amounts more frequently.
If you are dehydrated, you will need rehydration fluids (available from pharmacies).
Children and infants
Continue to breastfeed infants at risk of dehydration, or give them other milk feeds. Older children at risk of dehydration can be given diluted squash.
Avoid giving fruit juices and carbonated drinks.
If an infant or child is already dehydrated, they should be given rehydration fluids (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.
How much should I drink?
Studies have tried to establish a recommended daily fluid intake, but it can vary depending on the individual and factors such as age, climate and physical activity.
A good rule is to drink enough fluid so that you’re not thirsty for long periods, and to steadily increase your fluid intake when exercising and during hot weather. Passing clear urine (wee) is a good sign that you’re well hydrated.
You should drink plenty of fluid if you have symptoms of dehydration, such as feeling thirsty and lightheaded, or passing dark-coloured urine. It is also important to replace fluid lost after an episode of diarrhoea.