Dehydration - Symptoms 

Symptoms of dehydration 

Dehydration can be mild, moderate or severe, depending on how much of your body weight is lost through fluids.

Two early signs of dehydration are thirst and dark coloured urine. This is the body's way of trying to increase water intake and decrease water loss.

Other symptoms may include:

  • dizziness or light-headedness
  • headache 
  • tiredness
  • dry mouth, lips and eyes
  • passing small amounts of urine infrequently (less than three or four times a day)

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

You should be able to reverse dehydration at this stage by drinking more fluids, without medical attention.

If dehydration is ongoing (chronic), it can affect your kidney function and cause kidney stones to develop. It can also lead to:

  • liver, joint and muscle damage
  • cholesterol problems
  • constipation 

When to see your GP

See your GP if your symptoms continue despite drinking fluids, or if you suspect that your baby or toddler is dehydrated.

You should also contact your GP if your baby has passed six or more diarrhoeal stools in the past 24 hours, or if they have vomited three times or more in the past 24 hours.

If dehydration is suspected, you may be given a blood test or a urine test to check the balance of salts (sodium and potassium) in your body.

Severe dehydration

If dehydration is left untreated it can become severe.

Severe dehydration is a medical emergency and requires immediate medical attention.

Contact your GP or out-of-hours service straight away if you have any of the following symptoms:

  • feeling tired (lethargic) or confused
  • dry mouth and eyes that do not produce tears
  • not passing urine for eight hours
  • dry skin that sags slowly into position when pinched up
  • rapid heartbeat
  • blood in your stools (faeces) or vomit
  • low blood pressure (hypotension)  
  • irritability
  • sunken eyes
  • a weak pulse
  • cool hands and feet
  • fits (seizures)
  • a low level of consciousness

If severe dehydration is not treated immediately, it can lead to complications. You can even die from severe dehydration because the blood stops circulating.

This level of dehydration needs hospital treatment and you will be put on a drip to restore the substantial loss of fluids.

Page last reviewed: 17/05/2013

Next review due: 17/05/2015


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The 3 comments posted are personal views. Any information they give has not been checked and may not be accurate.

Snow Cat said on 19 July 2013

I think one of the best ways to rehydrate the body is to eat moisture containing foods, as these can work more effectively than just water alone. Those sorts of foods are things like fruit and salad vegetables. Water, although very important in hot weather, I think can sometimes pass too easily through the body to the bladder.

I think it is also important to eat some salt, as hot weather can easily get rid of the salt in your body and produce effects such as cramps. This is particularly so if a lot of water has been drunk, because the water is effectively flushing things out.

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Wiccy13 said on 22 April 2013

Im glad your son is on the mend sharon! I have recently been diagonosed with microscopic colitis, and the told i am dehydrated because of the colitis, hopefully i will be able to get back to normal soon and this is a great source of info but if anyone is worried about any of there symptoms or other health issues its always best to consult your gp

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airsharon said on 21 November 2012

Thank you for publishing this information - I took my son to A&E after googling for information. He was diagnosed at hospital as being severly dehydrated following sickness for 4 days - After a few days in hospital with their care he came home and is on the mend.

I think this post of information made me realise things were very bad, along with a mothers intuition as I know my child better than anyone else.

I was told he would probably have died if I had not acted so quickly - this informaiton was so very valuable - thank you :)

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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
  • dry mouth
  • fewer wet nappies
  • drowsiness
  • fast breathing

Read about how to treat dehydration in babies