What is a fever (high temperature) in children?

As a general rule a temperature of over 37.5C (99.5F) is a fever.

You can use a thermometer to find out if your child has a fever. For more information, see How do I take someone’s temperature?

Causes of fever

Most fevers are caused by an infection or other illness.

Fever helps your body fight infections by stimulating the body’s natural defences. By increasing the body’s temperature, a fever makes it harder for the bacteria and viruses that cause infections to survive.

Conditions that can cause fever include many viral infections such as flu and chickenpox and, if the child has not been fully immunised, measles and mumps.

Fevers can also be caused by:

Other things that may raise the temperature of a baby or child include:

  • overheating because of too much bedding or clothing  
  • being vaccinated
  • treating a fever

You can usually treat fever in young children at home using infant paracetamol. Read more information about treating a high temperature.

Getting help

If you’re worried about your child, trust your instincts. Speak to your GP or call NHS 111.

If your GP surgery is closed, contact the out-of-hours service. You will be informed about how to do this when you ring your GP’s phoneline. If you’re still concerned, or if your GP or out-of-hours provider can’t come quickly enough, take your child straight to the nearest hospital’s accident and emergency department.

Other symptoms

Symptoms that may be a sign of a more serious illness include:

  • being unusually sleepy
  • not drinking for more than eight hours
  • having a non-blanching rash (a rash that doesn’t fade when a glass is pressed firmly against the skin; this is known as the tumbler test

For more signs of serious illness and advice on when to call an ambulance for your child, see recognising signs of serious illness

Febrile convulsions

Febrile convulsions are seizures (or fits) that sometimes happen in children who have a high temperature. They are most common in children under three and are rare after the age of six.

Febrile convulsions can happen as a result of any illness that causes a high temperature. They can be frightening for parents but look much worse than they actually are. Febrile convulsions rarely cause any long-term complications.  

If the fit has not stopped within three minutes call 999.

If it is your child’s first ever seizure (or fit) and it has stopped and the child has fully recovered you should still seek medical advice.

About one in three children will have another febrile seizure when they are next ill, especially within the first year of their first seizure. 

Read more about febrile convulsions

Read the answers to more questions about children’s health.

Further information:

Page last reviewed: 09/08/2012

Next review due: 08/08/2014