what is dehydration: an introduction

What is dehydration?

Water makes up between 55-75% of the human body. It is needed to maintain the health and integrity of every cell in the body and is also necessary for most body functions. There are many ways we lose water on a daily basis. For example, we lose water from our lungs, from our skin through sweating and from urine. The body cannot store water, therefore we need to take in fresh supplies every day to replenish these losses. Dehydration occurs when the water content of the body is too low.1

Causes of dehydration

Dehydration may be caused by losing too much fluid, not drinking enough water or fluids, or both.2 Increased sweating (due to hot weather, exercise or fever), not drinking enough water or fluids, diarrhoea or vomiting can all lead to fluid loss. It may also be caused by increased urine output due to certain medications and medical conditions.1 When dehydration is found and treated quickly, the outcome is usually good. However, dehydration that is severe and left untreated, may lead to serious complications. It is important to monitor a person who is ill, especially an infant, child or elderly person. Begin fluid replacement as soon as diarrhoea or vomiting starts and do not wait for signs of dehydration to appear.2


Diarrhoea means that you have loose, watery stools more than three times in one day. It may also be accompanied by cramps, nausea and bloating. Diarrhoea may be caused by bacteria, viruses or parasites, food intolerances, certain medications and disorders that affect the stomach, small intestine or colon.3During diarrhoea, there is an increased loss of water and electrolytes. If these losses are not adequately replaced, a deficit of water and electrolytes develops, causing dehydration.4

Why are electrolytes important?

Electrolytes are minerals in your blood and body fluids that affect the amount of water in your body as well as the acidity of your blood, muscle function and other important processes. Examples of electrolytes include chloride, potassium and sodium. You lose electrolytes when you sweat and they must therefore be replaced along with water by drinking fluid.5 Electrolyte levels can become too low or too high when the amount of water in the body changes (causing either dehydration or overhydration). The imbalance in electrolytes can be caused by diarrhoea, vomiting, sweating, kidney problems and certain medications.6


Mild to Moderate Dehydration

There are varying degrees of dehydration. Mild to moderate dehydration may be caused by something as simple as not drinking enough water because you're sick or too busy, or because you lack access to safe drinking water while hiking or camping, for example.7 Mild to moderate dehydration may cause symptoms such as: 8
  • dry mouth
  • a lack of tears when crying
  • sleepiness
  • thirst
  • dry skin
  • headache
  • constipation
  • lightheadedness
  • decreased urine output
In infants a decrease in the output of urine translates to no wet nappies for three hours, and no urination for eight hours or more for older children and adolescents.8 Dehydration in babies and small children can be a life-threatening condition, therefore it is important to seek medical treatment immediately if you suspect dehydration. Seek medical advice if diarrhoea persists for more than:
  • six hours in infants less than 6 months
  • 12 hours in children aged 6 months to 3 years
  • 24 hours in children aged 3 to 6 years
  • 48 hours in children over 6 years of age
Children may also have symptoms such as cold skin, sunken fontanelle (the soft spot on a baby’s head) and a blue tinge to the skin, due to slowed circulation.1

Severe dehydration

Severe dehydration is a medical emergency and may cause signs and symptoms such as:8
  • extreme thirst
  • a very dry mouth and skin
  • lack of sweating
  • little or no urination
  • shrivelled skin
  • sunken eyes
  • low blood pressure
  • rapid breathing and heart rate
  • fever
  • adults may also be irritable and confused
  • children may exhibit extreme fussiness and/or sleepiness.

Oral Rehydration Therapy

When the body needs water, thirst unfortunately, is not the best indicator. A more reliable indicator is the colour of urine. When urine appears dark yellow or amber it usually indicates dehydration. When you are well hydrated urine is clear or light coloured. 8 Dehydration from diarrhoea can be treated in all age groups and in all but the most severe cases by giving patients an adequate glucose-electrolyte solution by mouth. This way of giving fluids is called oral rehydration therapy (ORT).9 Along with the United Nations International Children's Emergency Fund (UNICEF), the World Health Organization recommends the use of ORT for the prevention and treatment of dehydration due to diarrhoea.9