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
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 diarrhea, 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 dehydrated, drink plenty of fluids such as water, diluted squash or fruit juice. These are much more effective than large amounts of tea or coffee. Fizzy drinks may contain more sugar than you need and may be harder to take in large amounts.
If you're finding it difficult to keep water down because you're vomiting, try drinking small amounts more frequently.
Infants and small children who are dehydrated shouldn't be given large amounts of water alone as the main replacement fluid. This is because it can dilute the already low level of minerals in their body too much and lead to other problems.
Instead, they should be given diluted squash or a re-hydration 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.
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 diarrhea.