Dehydration in Children


To work properly, our bodies need to maintain a core temperature of about 37°C at all times. Body temperature is tightly controlled by a “thermostat” in a part of the brain called the hypothalamus. When the body’s core temperature rises above its “set point” the hypothalamus turns on various systems to help us lose excess heat. These include:

  • faster, shallower breathing
  • increased blood flow to the skin

We shed most of our excess heat through the skin. This is easy when the air around us is cool and dry, but it is more difficult in high temperatures, high humidity and direct sunlight. This is why summertime can bring the risk of heat-related illnesses.

Who is at risk for heat-related illness?

In the past, it was thought that children in general were more vulnerable to heat-related illnesses than adults. However, with adequate fluids, most children are able to regulate their body temperature as well as adults can.

Despite this, any child whose body has trouble regulating temperature or who cannot escape the heat is at risk when the temperature rises. This includes:

  • babies and young children – the surface area of their bodies is high compared to their body mass so they absorb more heat from the environment, produce more heat when exercising, sweat less than adults and may forget or not know to drink plenty of fluids
  • children with developmental disabilities – they may not recognize the need to replace fluids lost through sweating
  • children who cannot move or change position by themselves
  • children with chronic (long-term) illnesses such as diabetes, cystic fibrosis or heart conditions
  • children with acute illnesses, including fever, gastrointestinal infection or sunburn
  • children who exercise heavily, especially if they are not used to the heat, not very fit or obese
  • children who are taking certain drugs that reduce the body’s ability to regulate its temperature, such as antihistamines, diuretics or drugs for mental health conditions
  • any child who has had heat-related illness in the past.

Common heat-related illnesses

Heavy sweating without replacing lost fluids can lead to dehydration and heat cramps. If the body cannot shed enough heat for any reason, there is a risk of heat exhaustion and, in extreme cases, heat stroke – a medical emergency.

Heat cramps, heat exhaustion and heat stroke are more common risks for children and teens who engage in prolonged or intense physical activity in the sun, for example during sports practice. For other children, the main heat-related illness to consider is dehydration.


Children can become dehydrated when they lose more body fluid by sweating or urinating than they replace by drinking. Even a small amount of dehydration, amounting to just 2 per cent of body weight, can affect a child. Dehydration increases the risk of other heat-related illnesses because it interferes with the body’s ability to regulate temperature.

Symptoms of dehydration include:

  • dry or sticky mouth
  • thirst
  • low or no urine output; concentrated urine appears dark yellow
  • not producing tears
  • being irritable or cranky
  • seeming bored or uninterested
  • headache
  • dizziness
  • cramps
  • chills
  • fatigue

In severe cases, dehydration can cause:

  • sunken eyes
  • a sunken soft spot, or fontanelle, on the top of the head in an infant
  • nausea or vomiting
  • lethargy or coma.

What to do if you suspect your child is dehydrated

If you suspect your child is dehydrated, move them to a cool, shady area and give them plenty of water or clear juice. If they do not feel better soon, take them to see a doctor. If they are unconscious or unresponsive, take them to see a doctor right away.

Dehydration is the most common heat-related illness. If you suspect dehydration, take your child to a cool area and give him water or clear juice.

If dehydration is not treated correctly or if children are engaged in prolonged activity in direct sunlight, they can also develop heat cramps, heat exhaustion and, in severe cases, heat stroke.

To prevent a heat-related illness, stay out of direct sunlight, especially between 10am and 2pm, rest in shady areas, have your child drink water and dress them in lightweight, light-coloured and loose clothing.


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