Dehydration occurs when your body loses more fluid than you take into your body.

Signs and symptoms of dehydration 

Water makes up over two-thirds of the healthy human body. It lubricates the joints and eyes, helps digestion, flushes out waste and toxins, and keeps the skin healthy.

When the normal water content of your body is reduced, it upsets the balance of minerals (salts and sugar) in your body. This affects the way your body functions.

Signs of dehydration can vary depending on how much of your body weight is lost through fluids.

Early warning signs of dehydration include:

  • thirst
  • dark-coloured urine

 This is the body's way of trying to increase water intake and decrease water loss.

You should be able to reverse dehydration at this stage by drinking more fluids.

Dehydration can lead to a loss of strength and stamina. It's a main cause of heat exhaustion.

Dehydration in children 

Signs of moderate dehydration in a child include:

  • appears to be unwell or deteriorating
  • altered responsiveness (for example irritable, lethargic)
  • skin colour unchanged
  • decreased urine output
  • rapid breathing 
    • in a child of 6-12 months of age, of more than 50 breaths per minute
    • over 12 months of age, of more than 40 breaths per minute 
  • a faster heartrate than usual
    • over 160 beats per minute  is a fast heart rate in a child under 1 year of age
    • over 150 beats/minute in a child 1-2 years of age 
    • over 140 beats per minute in a child 2-5 years of age

Signs of severe dehydration in a child include:

  • decreased level of consciousness
  • pale or mottled skin
  • cold extremities, (that is, hands and feet)
  • more rapid breathing
  • an even faster heartrate

Dehydration in babies 

A baby may be dehydrated if they have:

  • a sunken soft spot (fontanelle) on their head
  • few or no tears when they cry
  • a dry mouth
  • fewer wet nappies
  • dark yellow urine
  • drowsiness
  • fast breathing
  • cold and blotchy-looking hands and feet

Dehydration in an adult 

Signs and symptoms of mild dehydration in an adult include:

Signs and symptoms of moderate dehydration in an adult include:

Your tongue may become dry and your eyes sunken. You may notice you produce less urine (pee), and your pulse may speed up.

Signs and symptoms of severe dehydration in an adult include:

  • increased apathy/weakness
  • becoming confused or losing consciousness
  • reduced or no urine output
  • pale appearance with a fast pulse

Severe dehydration 

If dehydration is left untreated, it can become severe.

Severe dehydration (see signs and symptoms above)  is a medical emergency and requires immediate medical attention.

If severe dehydration is not treated immediately, it can lead to complications.

Contact your GP, or the GP out of hours service straight away if you or your child have any of the signs of severe dehydration.

Treating dehydration 


  • the best way to treat dehydration is to rehydrate the body by drinking plenty of fluids - fruit juices and carbonated drinks should not be used
  • if you are breast feeding your baby, continue breastfeeding, or if bottle feeding continue milk feeds
  • a sweet drink can help to replace lost sugar, and a salty snack can help to replace lost salt
  • if you're finding it difficult to keep water down because you're vomiting, try drinking small amounts more often


  • if you think your baby is dehydrated, take them to see your GP as soon as possible -they'll be able to recommend appropriate treatments
  • give your baby plenty of liquids, such as breastmilk or formula -  it can often be better to give them smaller amounts of fluid more often
  • don't dilute your baby's formula (if you use it) -  babies who are formula-fed and those on solids can be given extra water
  • avoid giving your baby fruit juice, particularly if they have diarrhoea and vomiting, because it can make it worse
  • giving your baby regular sips (a few times an hour) of oral rehydration solution in addition to their usual feed (breastmilk, formula milk and water) will help to replace lost fluids, salts and sugars

Infants and children 

  • infants and children who are dehydrated shouldn't be given solely water, because it can dilute the already low level of minerals in their body and make the problem worse
  • instead, they should have diluted squash or a special oral rehydration solution  (see below)
  • if you or your child is finding it difficult to hold down fluids because of vomiting, take smaller amounts more often. You may find it easier to use a spoon or a syringe to give your child small amounts of fluid

Oral rehydration solutions 

When you're dehydrated, you lose sugar and salts, as well as water. Drinking a rehydration solution will enable you to re-establish the right balance of body fluids. Speak to your pharmacist about suitable oral rehydration solutions.

When to seek medical help 

You should see your GP if your symptoms continue despite drinking fluids. You should seek medical advice if your child appears to have moderate dehydration, and urgently if it appears severe (see above). Seek medical advice if you suspect that your baby or toddler is dehydrated.

You should also contact your GP if your child:

  • has had five or more episodes of diarrhoea in the past 24 hours
  • is 1 year or younger and has been vomiting for more than 12 hours
  • is under 2 and has been  vomiting for more than 24 hours
  • is 2 years or older and has been vomiting for more than 48 hours

You should contact your GP if you

  • have diarrhoea lasting more than 10 days
  • are vomiting for more than 2 days

Causes of dehydration

Dehydration is usually caused by not drinking enough fluid to replace what we lose.

Other factors that can contribute to dehydration include:

  • the climate
  • the amount of physical exercise you are doing (particularly in hot weather)
  • your diet
  • illness, such as persistent vomiting and diarrhoea, or sweating from a fever

People at risk from dehydration

Anyone can become dehydrated, but certain groups are particularly at risk. These include:

  • babies and infants – they have a low body weight and are sensitive to even small amounts of fluid loss
  • older people – they may be less aware that they are becoming dehydrated and need to keep drinking fluids
  • people with a long-term health condition – such as diabetes or alcoholism
  • athletes – they can lose a large amount of body fluid through sweat when exercising for long periods 

Preventing dehydration 

You should drink plenty of fluids to avoid becoming dehydrated.

Most of the time, you can prevent dehydration by drinking water regularly throughout the day. Be guided by your thirst. However in hot weather, when exercising and during illness, you should drink more.

As a guide, passing pale or clear-coloured urine (pee) is a good sign that you're well hydrated.


If you, your child or someone you are caring is ill, particularly with a fever, vomiting or diarrhoea, there's a high risk of becoming dehydrated. It's important to start replacing fluid as soon as possible.

Advice for children 

It is important for children to replace lost fluid, to prevent dehydration. Like adults, children lose more water when they are in hotter climates and when they are physically active.

You should give your child healthy drinks as part of an overall healthy, balanced diet.

How much you should drink

Studies have tried to establish a recommended daily fluid intake. However, it can vary depending on the individual and factors such as age, climate and physical activity. There is no single recommended amount (guidance is provided below for children, based on weight.)

A good rule is to drink enough fluid so that you're not thirsty for long periods. You should, steadily increase your fluid intake when exercising and during hot weather. Passing clear urine (pee) is a good sign that you're well hydrated.

You should drink plenty of fluid if you have symptoms of dehydration, such as feeling thirsty and lightheaded, or passing dark-coloured urine. It is also important to replace fluid lost after an episode of diarrhoea. 

Fluid guidance for children 

The amount of fluid your child needs in a day to stay hydrated depends on their weight. See below for guidance:

  • for a child who weighs 0–10 kg, the amount of fluid required per day is 100 ml/kg, (for example, 500ml/day if the child weighs 5kg)
  • for a child who weighs 10–20 kg, the amount of fluid required per day is 1000 ml plus 50 ml/kg for each kg over 10kg, (for example, 1250ml/day if the child weighs 15kg)
  • for a child who weighs more than 20 kg, the volume of fluid required per day is 1500 ml plus 20 ml/kg for each kg over 20 kg, (for example, 1600 ml/day if the child weighs 25 kg

Find out more about dehydration on the NHS website.

The information on this page has been adapted from original content from the NHS website.

For further information see terms and conditions.

This page was reviewed July 2017

This page is due for review April 2019

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