Introduction

Dehydration is when a child loses fluid, like water, from their body faster than it can be replaced.

Dehydration can be caused by:

  • vomiting 
  • diarrhoea – loose, watery poo
  • heat stroke – when the body becomes too hot for too long
  • taking medications that remove fluid from the body, like diuretics
  • not drinking enough fluid, especially when unwell
  • fever
  • lots of physical activity and exercise
  • hot weather.

Fluids are essential because they help to:

  • regulate body temperature
  • move nutrients through the body
  • flush out waste
  • make sure organs and tissues work properly.

Children are at higher risk for dehydration because they:

  • lose a lot of fluid through their skin
  • are more likely to get viruses that cause vomiting and diarrhoea
  • can’t always communicate that they are thirsty
  • depend on adults to give them a good amount of fluid throughout the day.

 Signs and symptoms

Dehydration can be mild or severe.  

Mild dehydration can cause symptoms like:

  • dizziness or feeling light-headed
  • nausea, or feeling sick
  • a dry mouth, tongue, lips or throat
  • dark yellow or brown urine
  • fewer wet nappies than usual
  • not needing to wee as much.

Severe dehydration is a medical emergency and can be life-threatening. 

It can cause symptoms like:

  • being very thirsty
  • pale skin
  • sunken eyes
  • no tears when crying
  • cold feeling in the hands and feet
  • faster breathing and heart rate
  • having no energy
  • feeling irritable and confused
  • electrolyte imbalance – where the body loses salts and minerals for essential bodily functions, like regulating the heart.

In babies, the soft spot in their head called the fontanelle will look or feel caved in.

If your child is showing signs of severe dehydration, call triple zero (000) for an ambulance or go to your nearest emergency department.

Diagnosis

Dehydration can be diagnosed based on your child’s symptoms and a urine test to check fluid levels in the body.

Your child’s doctor may do other tests if they are looking for the cause of the dehydration.

Treatment

Severe dehydration

Severe dehydration is treated in the hospital. Your child will be given fluids through an intravenous (IV) cannula, a thin tube that goes into the vein.

They will also be given small sips of oral rehydration fluid, a special liquid made to replace fluid and salts.

Mild dehydration in children

Mild dehydration can be treated at home by giving your child fluids.

Oral rehydration fluids are usually better than water because they help to replace essential salts and minerals called electrolytes.

You can buy oral rehydration fluids from the supermarket or chemist.

They come in forms like:

  • concentrated liquid to mix with water
  • iceblocks
  • tablets to dissolve in water
  • powders to mix with water
  • ready-to-drink bottles.

Follow the instructions on how to prepare and give oral rehydration fluids closely. They will usually need a specific amount of water to ensure the electrolytes are replaced properly.

Older children who weigh over 10kg will need at least 250 mL of fluids every hour for 4 hours.

If your child does not want to drink from a bottle or a cup, you can try using a syringe to give them smaller amounts of fluids every few minutes or feeding them fluid with a spoon.

If you don’t have oral rehydration fluids, apple juice can also be used when mixed with an equal amount of water.

Never give dehydrated children drinks that are high in sugar or caffeine, like flat lemonade or sports drinks. These can make dehydration worse by:

  • irritating the bladder and making your child go to the toilet more often
  • drawing water out of the body through high sugar content
  • not hydrating the body properly
  • causing an electrolyte imbalance.

Mild dehydration in babies

A doctor should always see babies under 6 months old if they are dehydrated. Babies under 6 months cannot have water or dairy milk.

For babies over 6 months old who have breastmilk from the breast or bottle:

  • can continue feeding on demand or, more often 
  • oral rehydration fluid or water can be given in the first 12 hours.

For babies over 6 months who are fed using infant formula:

  • formula must be replaced with oral rehydration fluid or water in the first 12 hours
  • they can have the formula again after 12 hours, in smaller but more frequent amounts.

Babies between 6-12 months cannot have dairy milk.

 Management

How much fluid your child should drink

Recommended amounts of fluid are a guide and will change depending on your child’s lifestyle, environment and how active they are. 

Babies 0-6 months – fluid through breastmilk or infant formula, no water or dairy milk.

Infants 6-12 months – fluid through breastmilk, infant formula, and small amounts of boiled, cooled water. No dairy milk.

Toddlers 1-3 years – around 4 cups of fluid, mainly water, breastmilk, and dairy milk.

Children 4-8 years – around 5 cups of fluid, mainly water.

Pre-teens 9-13 years – around 5-6 cups of fluid, mainly water.

Teenagers 13+ - around 6-8 cups of fluid, mainly water.

Keeping your child hydrated

Water should always be the first choice for children. Your child should drink a good amount of water regularly throughout the day.

Some children can forget to drink during the day and drink lots of water close to bedtime. This can cause them to wet the bed as their bladder is holding too much fluid.

Encourage your child to keep a water bottle with them during the day and take regular breaks to drink.

Children do not need drinks with:

  • sugar – like soft drinks, fizzy flavoured water, or juice
  • caffeine – like soft drinks, coffee, or energy drinks
  • extra salts or electrolytes – like sports drinks.

If your child plays high-intensity sports or is doing exercise like running or hiking, a low-sugar sports drink or electrolyte drink can be used alongside chilled water to keep them happy and hydrated.

Plain dairy milk is another great drink for children over 12 months old, with 97% of it being water and electrolytes. Children can fill up on milk, so avoid giving too much too close to mealtimes.

When to seek help

See your local doctor as soon as possible, or go to your nearest emergency department if your child:

  • has diarrhoea that lasts more than a few days
  • has been vomiting for more than 24 hours
  • can't keep any fluids down
  • vomits blood, or has bloody diarrhoea
  • has not been willing to drink anything for several hours
  • has not needed to urinate in the past 6 to 8 hours 
  • hasn't had a wet nappy for 4 to 6 hours.

Disclaimer

This factsheet is provided for general information only. It does not constitute health advice and should not be used to diagnose or treat any health condition.

Please consult with your doctor or other health professional to make sure this information is right for you and/or your child.

The Sydney Children’s Hospitals Network does not accept responsibility for inaccuracies or omissions, the interpretation of the information, or for success or appropriateness of any treatment described in the factsheet.

© Sydney Children’s Hospitals Network 2024