About dehydration

What is dehydration?

Dehydration occurs when the amount of water in your body is too low. Up to 75% of the body’s weight is made up of water, mostly found within our body’s cells. It is important we keep a balance of these fluids, as adequate hydration is essential for our body’s ability to function. There are many ways we lose fluids naturally. As we breathe humidified air leaves the body, as we sweat to cool the body and from urination. Drinking a the right amount of water to replace the natural loss of fluids on a regular basis is recommended as part of your daily routine.

What causes dehydration?

Dehydration can be caused by vomiting or diarrhoea. A significant loss of body water, and to varying degrees electrolytes, results in dehydration. Other causes include excessive sweating (from exercise or illness), increased urine output (from diuretics), fever or decreased fluid intake which may be due to nausea or loss of appetite.

Why are electrolytes important?

Electrolytes including sodium, chloride and potassium are lost during episodes of diarrhoea. These mineral salts are required by the body to help regulate nerve and muscle function, and to maintain fluid balance. In order for the body to function normally, it must keep the correct fluid balance within the cells, the space around the cells (interstitial fluid) and in the blood. Electrolytes play a role in maintaining this fluid balance.


Diarrhoea is a consequence of irritation to the intestinal lining and can be accompanied by vomiting. The irritation may be caused by bacterial or viral infections (although these are not the only causes of diarrhoea). Diarrhoea may cause the body to lose far more fluid and essential mineral salts than normal which can lead to dehydration.

Signs and symptoms of dehydration

Common signs of dehydration include thirst, lethargy, and drowsiness, a dry mouth or tongue, sunken eyes, no tears when crying or a decrease in urine output. When children are ill they often show signs of fatigue, restlessness and irritability which can make it difficult to increase fluids. Signs of a child becoming dehydrated are similar to an adult; however tend to appear more rapidly. This is because they may lose more fluid quickly. Young children, babies and the elderly are a particularly high risk group for dehydration. Seek medical advice if diarrhoea persists for more than:

  • 6 hours in infants under 6 months
  • 12 hours in children under 3 years
  • 24 hours in children aged 3-6 years
  • 48 hours in adults and children over 6 years.

Oral rehydration therapy

The World Health Organization (WHO) and the United Nations International Children’s Emergency Fund (UNICEF) currently recommend the use of oral rehydration therapy (ORT) for the management of dehydration due to diarrhoea. Oral rehydration therapy has been described as one of the most important medical advances. Having an appropriate balance of electrolytes in an oral rehydration solution is of the utmost importance to help assist rehydration.

Always read the label. Follow the directions for use. If symptoms persist, talk to your health professional. Vitamin supplements should not replace a balanced diet

For more information, please visit https://www.healthdirect.gov.au/dehydration

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