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Excessive thirst

It's normal for babies and children, especially toddlers, to drink a lot and pass lots of urine (wee). This is called habitual drinking. But excessive thirst and increased urination in babies, children and teenagers can be a sign of diabetes mellitus or diabetes insipidus.

What are diabetes mellitus and diabetes insipidus?

Diabetes mellitus, often just called diabetes, is not associated with having a brain tumour. It can be checked for by a doctor with a simple finger prick test.

If this test is normal, it may indicate that the excessive thirst is a symptom of diabetes insipidus.

In diabetes insipidus, the body can't concentrate the urine enough and so it passes too much water. This is usually caused by a disturbance of the hormones released by the pituitary gland, a part of the brain. Sometimes, this disturbance can be caused by a brain tumour. But it's important to note that diabetes insipidus is rare.

What are the signs to look out for?

Babies and young children will be unable to tell you that they're excessively thirsty. In this case, signs and symptoms to watch out for include:

  • unexplained weight loss
  • large volumes of urine (weeing a lot)
  • leaking from nappies.

Children and teenagers with diabetes insipidus will have:

  • excessive thirst – feeling thirsty all the time and feeling 'dry' no matter how much they drink (including waking up regularly at night to drink)
  • increased urination – needing to go to the toilet a lot and passing pale, watery urine.

If excessive thirst is caused by a brain tumour, other symptoms will often be present, in particular:

  • abnormal growth
  • delayed or arrested puberty.

You should look out for these symptoms carefully.

If your baby, child or teenager has increased thirst and urination, they should be seen urgently by a doctor to check whether this symptom is being caused by diabetes and, if so, what is causing the diabetes.

If symptoms appear suddenly or are severe, take your child to A&E or phone 999.

If you're a teenager and you're worried about increased thirst and urination (weeing), it's best to talk to your GP as soon as possible.

I think my child has a brain tumour, what should I do?

Brain tumours are rare, however, if you're worried, if a symptom persists or if your child has more than one of these symptoms then:

  • Talk to your doctor
    GP appointments are usually quite short, find out how to best prepare for your appointment
  • Get an eye test
    If your child's symptoms are limited to changes in vision and/or headaches, get their eyes tested by an optician before seeing your GP.