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.