Dehydration occurs when your body loses more fluid than you take in. Water makes up over two-thirds of the healthy human body. It lubricates the joints, lungs and eyes, aids digestion, flushes out waste and toxins and keeps the skin healthy. When the normal water content of the human body is reduced, it upsets the balance of minerals (salts and sugar) which affects the way that the body functions.
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.
Who is at risk from dehydration?
Anyone can become dehydrated, but certain groups are particularly at risk. These include:
Signs and symptoms 
Some of the early warning signs of dehydration include:
A baby may be dehydrated if it:
What should I do if someone has signs of dehydration?
It is important to drink plenty of fluids when dehydrated. This can be water, semi-skimmed milk, diluted squash or fruit juice, but avoid caffeine and fizzy drinks where possible. If you're finding it difficult to keep water down because you're vomiting or have diarrhoea, try drinking small amounts more frequently.
Water should not be given to dehydrated infants and children as the main replacement fluid as it can exacerbate the problem by diluting the already low level of minerals in their body. Instead, they should be given diluted squash, diluted fruit juice or a full sugar fizzy drink that has been left to go to flat or a rehydration solution. A teaspoon or oral syringe can be helpful for getting fluid into infants carefully via the mouth.
Rehydration sachets help replace fluids and salts lost through heat exhaustion and sun exposure as well as diarrhoea and vomiting. You can buy sachets of rehydration salts from pharmacies in most countries. They are added to water and when drank, they provide the correct balance of water, salt and sugar to enable optimal rehydration. It is not recommended to use homemade salt or sugar drinks as these may cause further dehydration if not balanced correctly.
While most people recover when treated appropriately, severe dehydration can be serious and cause fits (seizures), brain damage and death if left untreated.
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