Dehydration
Introduction
Dehydration happens when your body loses more fluid than you take in. 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 that 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 skin healthy.
Some of the early warning signs that you're dehydrated include:
- feeling thirsty and lightheaded
- 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
- few or no tears when they cry
- fewer wet nappies
- drowsiness
The body is affected even when you lose a small amount of fluid. Read more about the symptoms of dehydration.
Who is at risk from dehydration?
Anyone can become dehydrated, but certain groups are particularly at risk. These include:
- babies and infants, because they have a low body weight and are sensitive to even small amounts of fluid loss
- older people, because they may be less aware that they're becoming dehydrated and need to keep drinking fluids
- people with a long-term condition, such as diabetes or alcoholism
- athletes, because they lose a large amount of body fluid through sweat
What to do
If you're dehydrated, drink plenty of fluids. This can be water, semi-skimmed milk and diluted squash or fruit juice, but it's best to avoid fizzy drinks or caffeine if possible. If you're finding it hard to keep water down because you're vomiting or have diarrhoea, try drinking small amounts more frequently (perhaps using a teaspoon or syringe for an infant or child).
If you or your child are dehydrated due to watery diarrhoea or excessive vomiting (hypernatraemic dehydration), try not to drink only water as it's likely to further dilute the minerals in the body and make the problem worse. Try drinking diluted juice, squash or a rehydration solution (available from pharmacies).
If left untreated, severe dehydration can be serious and cause fits (seizures), brain damage and death.
Read more about treating dehydration.
When should I see my GP?
You should visit your GP if your symptoms continue, despite drinking plenty of fluids or if you suspect that your baby or toddler is dehydrated.
If your doctor suspects dehydration, you may be given a blood test or a urine test to check the balance of salts (sodium and potassium) in your body.
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 don't 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)
Also contact your GP if you or your child has diarrhoea that lasts longer than five days, or vomiting that lasts more than 24 hours in adults or 12 hours in a child.
How does dehydration happen?
Dehydration is usually caused by not drinking enough fluid or by losing fluid and not replacing it. The climate, the amount of physical exercise you're doing and your diet can also contribute to dehydration.
You can become dehydrated as a result of an illness, such as gastroenteritis, where you have persistent vomiting and diarrhoea, after sweating excessively from a fever, exercising in hot conditions or if you're urinating more frequently – for example, if you have diabetes.
Drinking too much alcohol can also cause dehydration, which is the main symptom of a hangover.
Read more about the causes of dehydration.
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Symptoms
Depending on how much of your body weight is lost through fluids, dehydration can be described as mild, moderate or severe.
Mild to moderate dehydration
The first sign of dehydration is thirst. Other symptoms may include:
- dizziness or light-headedness
- headache
- tiredness
- dry mouth, lips and eyes
- concentrated urine (dark yellow)
- passing only small amounts of urine infrequently (less than three or four times a day)
Moderate dehydration causes you to lose strength and stamina. It's the primary cause of heat exhaustion. You should be able to reverse mild to moderate dehydration 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 cause:
- liver, joint and muscle damage
- cholesterol problems
- constipation
Severe dehydration
Untreated mild or moderate dehydration can lead to severe dehydration.
Severe dehydration is a medical emergency and requires immediate medical attention. You should seek medical attention if you or your child has any of the following symptoms:
- dry, wrinkled skin that sags slowly into position when pinched up
- an inability to urinate, or not passing urine for eight hours
- irritability
- sunken eyes
- low blood pressure (hypotension)
- a weak pulse
- a rapid heartbeat
- cool hands and feet
- fits (seizures)
- a low level of consciousness
- feeling tired (lethargic) or confused
- blood in your stools (faeces) or vomit
If not treated immediately, severe dehydration can lead to complications. You can even die from severe dehydration because the blood stops circulating. If you experience this level of dehydration, you may need to be admitted to hospital and be put on a drip to restore the substantial loss of fluids.
When should I see my GP?
You should visit your GP if your symptoms continue, despite drinking plenty of fluids or if you suspect that your baby or toddler is dehydrated.
If your doctor suspects dehydration, you may be given a blood test or a urine test to check the balance of salts (sodium and potassium) in your body.
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 don't 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)
Also contact your GP if you or your child has diarrhoea that lasts longer than five days, or vomiting that lasts more than 24 hours in adults or 12 hours in a child.
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Causes
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 often depend on a number of factors, such as climate, level of physical activity and diet.
Dehydration is also linked to a number of other factors, which are outlined below.
Illness
Dehydration is often the result of an illness, such as gastroenteritis, where fluid is lost through persistent diarrhoea and vomiting.
Sweating
You can also become dehydrated after sweating excessively from a fever, heavy work in hot conditions or exercise and sport.
In these situations it's important that you 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 that it makes you urinate more.
The headache associated with a hangover indicates that your body is dehydrated. This is why it's important to drink plenty of water when you've been drinking alcohol.
Diabetes
If you have diabetes, you're at risk of dehydration 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 urinating more frequently.
Read more about the different types of diabetes.
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Treatment
The best way to treat dehydration is to rehydrate the body by drinking plenty of fluids, such as water, diluted squash, diluted fruit juice or semi-skimmed milk.
A sweet drink can help to replace lost sugar. A salty snack can help to replace lost salt.
Infants and children who are dehydrated shouldn't be given water as the main replacement fluid because it can further dilute the minerals in their body and make the problem worse. Instead, they should be given diluted squash, diluted fruit juice or a special rehydration solution.
If you or your child is finding it difficult to hold down fluids because of vomiting or diarrhoea, take smaller amounts more frequently. If necessary, you could use a spoon or a syringe to give your child small amounts of fluids.
Rehydration solutions
If you're dehydrated, you will have lost 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.
Several different rehydration products are available from pharmacies or on prescription from your GP, including solutions that are suitable for infants and children. Ask your GP or pharmacist for advice.
Severe dehydration
If you suspect that someone is severely dehydrated, you should seek medical attention immediately. 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 via a saline drip into a vein because this provides essential nutrients faster than using solutions that you drink.
If you've had bowel surgery, some rehydration solutions may not contain enough salt. In this case, you'll need a higher-strength solution. Your GP or surgeon will be able to recommend a suitable rehydration solution for you.
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Prevention
To avoid becoming dehydrated you should drink plenty of fluids. The Food Standards Agency (FSA) recommends that if you live in the UK (or somewhere with a similar climate), you should drink six to eight glasses of fluid every day.
As well as water, the FSA recommends semi-skimmed milk, diluted fruit juice and diluted squash.
Drinking 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.
When exercising, you should drink up to 1 litre (2 pints) of fluid each hour of exercise on top of your normal daily amount. This should be increased if you're exercising in warm conditions because you will sweat more and fluid will be lost from your body more rapidly.
Also be aware that drinking more fluid than your body can process can lead to a low amount of sodium in the blood (hyponatremia). This is a serious and potentially fatal condition. If you start to feel discomfort and bloating from drinking, you should allow time to recover.
Illness
If you, your child or someone you're caring for is ill, it's important to monitor how much fluid they're drinking. If you or they have a fever, are vomiting or have diarrhoea, it's highly likely that dehydration will occur. Therefore 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 very important for children to replace lost fluid to prevent dehydration. Like adults, children lose more water when they're in hotter climates and when they're physically active.
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