Thirst is normally just the brain's way of warning that you're dehydrated. Dehydration happens when you're not drinking enough fluid.
But excessive and persistent thirst could be a sign of an underlying problem such as diabetes.
Common causes of thirst
You will usually feel thirsty because you're not drinking the amount of fluid your body needs.
This may be because you've been sweating heavily or you've lost fluid because you have diarrhoea and are vomiting.
Having a drink of water will help you feel less thirsty (restore the fluid balance in your body). You should make sure you stay well hydrated.
It's particularly important to stay well hydrated:
- during hot weather
- while exercising
- while you're unwell with vomiting and diarrhoea
In some cases, thirst may be caused by something as simple as a recent meal or snack. Eating salty or spicy foods can cause you to suddenly feel thirsty.
If you feel thirsty all the time, it could be a sign of diabetes. This is particularly if you also have other symptoms.
- needing to urinate often
- extreme tiredness (fatigue)
- unexplained weight loss
Diabetes is a lifelong condition. The condition makes it difficult to control the level of sugar (glucose) in your blood.
The high levels of glucose can mean your kidneys need to produce more urine. This is to help pass the glucose out of your body.
This can make you feel thirsty. This is because your brain is telling you to drink more to make up for the fluids you've lost.
If you feel thirsty all the time and have other symptoms, your GP will probably carry out a blood glucose test to see whether you have diabetes.
Feeling thirsty, as well as urinating more often than usual, is a common symptom in pregnancy. It is usually nothing to worry about. Read more about urinating a lot in pregnancy.
Very occasionally, these problems can be a sign of gestational diabetes. This is a type of diabetes that affects women during pregnancy.
You should be screened for this as part of your antenatal care if you're at risk.
Excessive thirst can sometimes be a side effect of certain types of medication. If you think a particular medicine is causing your thirst, speak to your pharmacist for advice.
If thirst is a possible side effect of medication you are taking, it may be possible to change to a different medicine or reduce your dose. Speak to your GP about this.
Other causes of thirst
There are also many other potential causes of severe thirst. These include:
- diabetes insipidus – a condition caused by problems with a hormone that regulates the amount of fluid in the body
- diabetic ketoacidosis – a dangerous complication of diabetes caused by a lack of the hormone insulin in the body
- sickle cell anaemia – an inherited blood disorder
- psychogenic polydipsia – where a person with a mental health condition, such as schizophrenia, drinks excessive amounts of water that can't be excreted (got rid of) by the kidneys
- excessive bleeding
Some people think they're thirsty when they actually have a dry mouth. It's important to know the difference between the two. This is because they can have different causes.
For example, a dry mouth can be caused by feelings of anxiety, certain medications, or Sjögren's syndrome.