Authored by , Reviewed by Dr Adrian Bonsall on | Certified by The Information Standard

Although dehydration can be mild and just needs you to drink extra fluids, it can also be very severe and life-threatening.

Dehydration means your body does not have enough fluid. This may be because you haven't drunk enough fluid to replace the fluids you have lost, such as when sweating or in your wee (urine). If dehydration isn't treated it can get worse and become a serious problem.

See also the separate leaflets called Gastroenteritis and Gastroenteritis in Children.

The causes of lack of fluid in the body (dehydration) include:

  • Not drinking enough fluids.
  • Being sick (vomiting).
  • Diarrhoea.
  • Being exposed to the sun in hot weather for long periods ('sunstroke').
  • Drinking too much alcohol.
  • Excess sweating.
  • High temperature (fever).
  • Taking certain medicines called diuretics that reduce the amount of fluid in your body.

Babies, young children, the elderly and people with diabetes are at increased risk of dehydration.

Dehydration symptoms

The symptoms of lack of fluid in the body (dehydration) include:

  • Feeling thirsty.
  • Dark yellow and strong-smelling wee (urine).
  • Feeling dizzy or light-headed.
  • Feeling very tired.
  • Dry mouth, lips and eyes.
  • Weeing less urine and less often.

However the symptoms and signs vary depending on age and the severity of dehydration.

Signs of dehydration in adults

The signs of mild or moderate dehydration include:

  • Thirst.
  • Dry or sticky mouth.
  • Not peeing very much.
  • Dark yellow pee.
  • Dry, cool skin.
  • Headache.
  • Muscle cramps.

Signs of severe dehydration

  • Not peeing, or having very dark yellow pee.
  • Very dry skin.
  • Feeling dizzy.
  • Rapid heartbeat.
  • Rapid breathing.
  • Sunken eyes.
  • Sleepiness, lack of energy, confusion or irritability.
  • Fainting.

Severe dehydration is a medical emergency and needs immediate treatment.

Drink lots of fluids. If it's difficult to drink or you keep being sick (vomiting) then keep taking small sips of fluid and gradually drink more if you can.

If you're being sick or have diarrhoea and are losing too much fluid, you need to put back the sugar, salts and minerals that your body has lost. Your pharmacist can recommend oral rehydration powder sachets.

Speak with your doctor or nurse for advice if your symptoms don't improve or you have any concerns. Call 111 (in the UK) if you can't speak to your GP or don't know what to do next.

Call 999 (in the UK) or go to Accident and Emergency (A&E) if you have any signs of severe lack of fluid in the body (dehydration), such as:

  • Feeling very weak and tired.
  • Feeling confused or disorientated.
  • Dizziness.
  • Not having passed wee (urine) for eight hours.
  • Your pulse feeling weak and rapid.  

It's quite common for young children to become lacking in fluid (dehydrated). It is often mild but can be serious if it's not dealt with quickly. Babies and young children need plenty of fluids to avoid dehydration.

Signs of dehydration in babies, infants, toddlers and young children

The signs of dehydration include:

  • Dry mouth and tongue
  • No tears when crying
  • Dry nappies for over 3 hours
  • Sunken eyes and cheeks
  • Sunken soft spot on the top of the skull (fontanelle) in babies
  • Sleepiness, lack of energy, or irritability

Treatment of dehydration in babies and young children

  • You should continue breastfeeding or using formula. Give smaller quantities of milk more often than usual. Don't make formula weaker by diluting it with water.
  • Give small children their usual diet.
  • Give frequent small sips of extra water.
  • Use rehydration powder sachets, if available, to replace lost sugars, salts and minerals, as well as the fluid lost.
  • Avoid fruit juice or fizzy drinks because they can make diarrhoea or sickness (vomiting) worse.

Contact your doctor urgently or call an ambulance if your child displays any of the following signs or symptoms of dehydration:

  • Seems drowsy.
  • Is breathing fast.
  • Has a dry mouth.
  • Has dark-yellow wee.
  • Has cold and blotchy-looking hands and feet.

Further reading and references

  • ; NICE Clinical Guideline (April 2009)

  • ; Oral versus intravenous rehydration for treating dehydration due to gastroenteritis in children. Cochrane Database Syst Rev. 2006 Jul 19(3):CD004390.

  • ; The management of children with gastroenteritis and dehydration in the emergency department. J Emerg Med. 2010 Jun38(5):686-98. doi: 10.1016/j.jemermed.2008.06.015. Epub 2009 Apr 5.

  • ; NICE CKS, September 2017 (UK access only)

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