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Dehydration - A Guide

Dehydration is a condition that occurs when the loss of body fluids, mostly water, is more than amount that is taken in. With dehydration, more water is moving out of our cells and bodies than what we take in through drinking.

Overview
Symptoms
Cause
Treatment
Prevention


Overview

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

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

Some of the early warning signs of dehydration include:

  • feeling thirsty and lightheaded
  • a dry mouth
  • tiredness
  • having dark coloured, strong-smelling urine
  • passing urine less often than usual

A baby may be dehydrated if they:

  • have a sunken soft spot (fontanelle) on their head
  • have few or no tears when they cry
  • have fewer wet nappies
  • are drowsy

The body is affected even when you lose a small amount of fluid.

Dehydration is usually caused by not drinking enough fluid to replace what we lose. The climate, the amount of physical exercise you are doing (particularly in hot weather) and your diet can contribute to dehydration.

You can also become dehydrated as a result of an illness, such as persistent vomiting and diarrhoea, or sweating from a fever.

Who is 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 

What to do

If you're dehydrated, drink plenty of fluids such as water, diluted squash or fruit juice. These are much more effective than large amounts of tea or coffee. Fizzy drinks may contain more sugar than you need and may be harder to take in large amounts.

If you're finding it difficult to keep water down because you're vomiting, try drinking small amounts more frequently.

Infants and small children who are dehydrated shouldn't be given large amounts of water alone as the main replacement fluid. This is because it can dilute the already low level of minerals in their body too much and lead to other problems.

Instead, they should be given diluted squash or a rehydration solution (available from pharmacies). You might find a teaspoon or syringe can be helpful for getting fluid into a young child.

If left untreated, severe dehydration can be serious and cause fits (seizures), brain damage and death.

When to see your GP

See your GP if your symptoms continue, despite drinking plenty of fluids, or if you think your baby or toddler is dehydrated.

If your GP suspects dehydration, you may have a blood test or a urine test to check the balance of salts (sodium and potassium) in your body.

Contact your GP, out-of-hours service or NHS 111 straight away if you have any of the following symptoms:

  • extreme thirst
  • feeling unusually tired (lethargic) or confused
  • not passing urine for eight hours
  • rapid heartbeat
  • dizziness when you stand up that doesn't go away after a few seconds

You should also contact your GP if your baby has had six or more episodes of diarrhoea in the past 24 hours, or if they have vomited three times or more in the past 24 hours. 

How much should I drink?

Studies have tried to establish a recommended daily fluid intake, but it can vary depending on the individual and factors such as age, climate and physical activity.

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


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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 a main cause of heat exhaustion.

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

If dehydration is ongoing (chronic), it can affect your kidney function and increase the risk of kidney stones. It can also lead to muscle damage and 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 had six or more episodes of diarrhoea 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, out-of-hours service or NHS 111 straight away if you have any of the following symptoms:

  • feeling unusually tired (lethargic) or confused, and you think you may be dehydrated
  • dizziness when you stand up that doesn't go away after a few seconds
  • not passing urine for eight hours
  • a weak pulse
  • a rapid pulse
  • fits (seizures)
  • a low level of conciousness

If severe dehydration is not treated immediately, it can lead to complications. This level of dehydration needs hospital treatment and you will be put on a drip to restore the substantial loss of fluids.

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


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Causes of dehydration 

Dehydration is caused by not drinking enough fluid or by losing more fluid than you take in. Fluid is lost through sweat, tears, vomiting, urine or diarrhoea.

The severity of dehydration can depend on a number of factors, such as climate, level of physical activity and diet.

There are several causes of dehydration, which are described below.

Illness

Dehydration is often the result of an illness, such as gastroenteritis, where fluid is lost through persistent bouts of diarrhoea and vomiting.

Sweating

You can also become dehydrated if you sweat excessively after a fever, exercise, or carrying out heavy, manual work in hot conditions.

In these situations, it's important to drink regularly to replace lost fluids. It doesn't necessarily need to be hot for you to lose a significant amount of fluid from sweating.

Children and teenagers are particularly at risk because they may ignore the symptoms of dehydration, or not know how to recognise and treat them.

Alcohol

Dehydration can also occur as a result of drinking too much alcohol. Alcohol is a diuretic, which means it makes you wee more.

The headache associated with a hangover indicates that your body is dehydrated. You should try to drink plenty of water when you have been drinking alcohol.

Diabetes

If you have diabetes, you're at risk of becoming dehydrated because you have high levels of glucose in your bloodstream. Your kidneys will try to get rid of the glucose by creating more urine, so your body becomes dehydrated from going to the toilet more frequently.

Read more about the different  types of diabetes.

Who's at risk?

The groups of people most at risk of dehydration are:

  • babies and infants – their low body weight makes them sensitive to even small amounts of fluid loss
  • older people – they may be less aware they're becoming dehydrated and need to drink 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

Hyponatremia

It's possible to become overhydrated while exercising. This is known as hyponatremia and it's caused by low sodium (salt) levels in the blood. It can occur if too much water is drunk over a short period of time.

Hyponatremia sometimes affects athletes whose blood sodium level is reduced through sweat and then diluted by drinking large amounts of water.

Symptoms of hyponatremia include nausea, vomiting and headache. In serious cases, the brain can swell, causing confusion, seizures, comaand, in rare cases, death.

 


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Treating dehydration 

The best way to treat dehydration is to rehydrate the body by drinking plenty of fluids, such as water,diluted squash or diluted fruit juice.

A sweet drink can help to replace lost sugar, and a salty snack can help to replace lost salt.

Babies

If your baby is dehydrated, take them to see your GP as soon as possible. They'll be able to recommend appropriate treatments, such as those outlined below.

Give your baby plenty of liquids, such as breastmilk or formula. It can often be better to give them smaller amounts of fluid more frequently.

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 (ORS) 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 ORS (see below).

If you or your child is finding it difficult to hold down fluids because of vomiting, take smaller amounts more frequently. 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. The solution should contain a mixture of potassium and sodium salts, as well as glucose or starch.

There are several different rehydration products available over the counter from pharmacies or on prescription from your GP, including solutions that are suitable for infants and children.

Ask your GP or pharmacist for advice about the most suitable rehydration solution for you or your child.

Severe dehydration

Seek immediate medical help if you suspect someone is severely dehydrated.

They may need to be admitted to hospital for treatment. In particular, babies, infants and elderly people will need urgent treatment if they become dehydrated.

Fluid may be given up the nose using a nasogastric tube or using a saline drip into a vein (intravenously). This will provide essential nutrients faster than using solutions that you drink.

If you have had bowel surgery, some rehydration solutions may not contain enough salt. In this instance, you will need a higher-strength solution. Your GP or surgeon can recommend a suitable rehydration solution for you.


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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, but be aware that in hot weather, when exercising and during illness, you should drink more.

Mild dehydration can be relieved by drinking more water and diluted fruit squash. If necessary, you can purchase oral rehydration solutions (ORS) from a pharmacy. As a guide, passing pale or clear-coloured urine (wee) is a good sign that you're well hydrated.

Drink regularly

If you're active, or if the weather is particularly hot, there's a greater risk that you will become dehydrated. To prevent becoming dehydrated, you should increase your fluid intake.

As different people sweat at different rates, it's very difficult to provide specific recommendations about how much fluid you should drink. However, you should drink more than normal while exercising, and it's particularly important to keep well hydrated if you're exercising in warm conditions. This is because you will sweat more and fluid will be lost from your body more rapidly.

Rarely, drinking more fluid than your body can process can reduce the amount of sodium (salt) in your blood. This can lead to a serious and potentially fatal condition called hyponatremia. If you start to feel discomfort and bloating from drinking, stop drinking and allow time to recover.

Illness

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

Advice for children

There are no specific recommendations regarding the amount of water or other fluids that children need.

However, it's 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.

See the page on drinks and cups for more information and advice on specific drinks for young children.

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