Introduction

A febrile seizure is a fit that can happen when a child has a fever.

Febrile seizures are also sometimes called febrile convulsions. They are relatively common and, in most cases, aren't serious.

Around one in 20 children will have at least one febrile seizure at some point. They most often occur between the ages of six months and three years.

During a febrile seizure, the child's body usually becomes stiff, they lose consciousness and their arms and legs twitch. Some children may wet themselves. This is known as a tonic clonic seizure.

Read more about the symptoms of febrile seizures

What to do during a seizure

If your child is having a febrile seizure, place them in the recovery position. Lay them on their side, on a soft surface, with their face turned to one side. This will stop them swallowing any vomit, keep their airway open and help prevent injury.

Stay with your child and try to make a note of how long the seizure lasts.

If it's your child's first seizure, or it lasts longer than five minutes, take them to the nearest hospital as soon as possible, or dial 999 for an ambulance. While it's unlikely that there's anything seriously wrong, it's best to be sure.

If your child has had febrile seizures before and the seizure lasts for less than five minutes, phone your GP or the NHS 24 111 service for advice.

Don't put anything, including medication, in your child’s mouth during a seizure because there's a slight chance that they might bite their tongue.

Almost all children make a complete recovery after having a febrile seizure.

Read more about diagnosing febrile seizures and treating febrile seizures

Types of febrile seizure

There are two main types of febrile seizure.

Simple febrile seizure

A simple febrile seizure is the most common type of febrile seizure, accounting for about eight out of 10 cases. It's a fit that:

  • is a tonic clonic seizure (see above)
  • lasts less than 15 minutes
  • doesn't reoccur within 24 hours or the period in which your child has an illness

Complex febrile seizure

Complex febrile seizures are less common, accounting for two out of 10 cases. A complex febrile seizure is any seizure that has one or more of the following features:

  • the seizure lasts longer than 15 minutes
  • your child only has symptoms in one part of their body (this is known as a partial or focal seizure)
  • your child has another seizure within 24 hours of the first seizure, or during the same period of illness
  • your child doesn't fully recover from the seizure within one hour

Why febrile seizures occur

The cause of febrile seizures is unknown, although they're linked to the start of a fever (a high temperature of 38C (100.4F) or above).

In most cases, a high temperature is caused by an infection such as:

There may also be a genetic link to febrile seizures because the chances of having a seizure are increased if a close family member has a history of them. Around one in four children affected by febrile seizures has a family history of the condition.

Read more about the causes of febrile seizures

Complications

Febrile seizures have been linked to an increased risk of epilepsy, as well as other problems.

Recent research findings may indicate a link between febrile seizures and sudden unexplained death in childhood (SUDC), possibly due to the connection between febrile seizures and epilepsy.

However, this link hasn't been proven and SUDC is incredibly rare, affecting around one in 100,000 children which is equivalent to a 0.001% chance.

In addition, one of the biggest studies of its kind looked at more than 1.5 million children with a history of febrile seizures and found no evidence of an increased risk of death in later childhood or adulthood.

Febrile seizures and epilepsy

Many parents worry that if their child has one or more febrile seizures, they'll develop epilepsy when they get older. Epilepsy is a condition where a person has repeated seizures without fever.

While it's true that children who have a history of febrile seizures have an increased risk of developing epilepsy, it should be stressed that the risk is still small.

It's estimated that children with a history of simple febrile seizures have a one in 50 chance of developing epilepsy in later life. Children with a history of complex febrile seizures have a one in 20 chance of developing epilepsy in later life.

This is compared to around a one in 100 chance for people who haven't had febrile seizures.

Symptoms

The main symptom of a febrile seizure is a fit that occurs while a child has a fever.

Febrile seizures often occur during the first day of a fever, which is defined as a high temperature of 38C (100.4F) or above. 

However, there appears to be no connection between the extent of your child’s fever and the start of a seizure. Seizures can occur even if your child has a mild fever.

Simple febrile seizures can happen when there's a rapid rise in temperature and you may only realise your child is ill when they have a fit. Alternatively, they can occur as your child’s temperature drops from a high level.

During simple febrile seizures:

  • your child’s body will become stiff and their arms and legs will begin to twitch
  • they'll lose consciousness and they may wet or soil themselves
  • they may also vomit and foam at the mouth and their eyes may roll back
  • the seizure usually lasts for less than five minutes
  • following the seizure, your child may be sleepy for up to an hour afterwards

Complex febrile seizures tend to last longer than 15 minutes, and the symptoms may only affect one area of your child's body. The seizure sometimes recurs within 24 hours or during the period in which your child is ill.

Seeking medical advice

You should take your child to hospital or dial 999 for an ambulance if:

  • your child is having a fit for the first time
  • the seizure lasts longer than five minutes and shows no signs of stopping
  • you suspect the seizure is being caused by another serious illness, for example meningitis
  • your child is having breathing difficulties

If your child has previously had febrile seizures, it's recommended that you telephone your GP or call the NHS 24 111 service for advice.

You should also contact your GP or the NHS 24 111 service if your child shows signs and symptoms of dehydration (a lack of fluid in the body). This includes:

  • dry mouth
  • sunken eyes
  • a lack of tears when crying
  • a sunken fontanelle – the soft spot usually found at the top of a young child’s head

Causes

Febrile seizures are linked to fevers, but the exact cause is unknown.

Some researchers think that the biological processes associated with a high temperature may be responsible.

A high temperature is thought to be caused by a bacterial or viral infection that stimulates the release of cytokines. Cytokines are proteins that affect the parts of the brain and nervous system responsible for regulating the body’s temperature. Their release causes a rise in the body's temperature.

One theory is that in certain people, high levels of cytokines may temporarily ‘scramble’ the workings of the brain and nervous system, triggering a seizure.

Family history

Although febrile seizures are poorly understood, a family history of the conditions is thought to increase the risk. 

If a child has a first-degree relative (mother, father, sister or brother) with a history of febrile seizures, their risk of having seizures increases. The more relatives affected, the higher the risk.

This is probably the result of one or more genetic mutations that a child inherits from their parents, which makes them more susceptible to seizures. A genetic mutation means the instructions carried in certain genes become ‘scrambled’, resulting in some of the body’s processes not working in the normal way.

Associated infections

Most febrile seizures occur when a child has a high temperature caused by an infection. The three most common infections associated with febrile convulsions are:

Other infections associated with febrile seizures are:

  • urinary tract infections (UTIs)
  • upper respiratory tract infection – an infection of the mouth, nose and throat, and associated tissues and structures
  • gastroenteritis – an infection of the digestive system
  • lower respiratory tract infections, such as pneumonia (a lung infection) and bronchitis (an infection of the airways that supply the lungs)

Vaccinations

In rare cases, febrile seizures can occur after a child has a vaccination. Research has shown that your child has a one in 3,000 to 4,000 chance of having a febrile seizure after having the MMR vaccine.

The risks are even lower with the DTaP/IPV/Hib vaccine – a one in 11,000 to 16,000.

Diagnosis

Febrile seizures can often be diagnosed from a description of what happened.

Further tests may be needed if the cause of the associated infection isn't clear.

It's unlikely that your doctor will see the seizure, so an account of what happened is useful.

It's useful to know:

  • how long the seizure lasted
  • what happened – body stiffening, twitching of the face, arms and legs, staring and loss of consciousness
  • whether your child recovered within one hour
  • whether they've had a seizure before

Tests to identify the source of the infection will only usually be necessary to rule out rarer conditions which can cause similar symptoms, such as meningitis.

A blood or urine sample may be needed to test for signs of infection. It can sometimes be difficult to obtain a urine sample from young children, so it may have to be done in hospital.

Read more about blood tests

Further tests

Further tests may be carried out in hospital if your child’s symptoms are unusual – for example, if they don't have a high temperature or their seizures don't follow the normal pattern.

Further testing and observation in hospital is also usually recommended if your child is having complex febrile seizures.

Your child may have other tests including an electroencephalogram and lumbar puncture, particularly if they're less than 12 months old.

These two tests are explained below.

Electroencephalogram

An electroencephalogram (EEG) measures your child’s electrical brain activity through electrodes that are placed on their scalp. Unusual patterns of brain activity can sometimes indicate epilepsy.

However, some studies have suggested that an EEG may not be useful in many cases of febrile seizures.

Lumbar puncture

During a lumbar puncture, a small sample of cerebrospinal fluid (CSF) is removed for testing. CSF is a clear fluid that surrounds and protects the brain and spinal cord.

A hollow needle is inserted into the base of the spine to obtain the CSF sample. During the procedure, local anaesthetic will be used to numb your child’s back so that they don't feel any pain.

A lumbar puncture can be used to determine whether your child has an infection of the brain or nervous system.

Treatment

In many cases, febrile seizures do not need to be treated, although care should be taken to deal with a seizure as it happens.

What to do during a seizure

If your child is having a febrile seizure, place them in the recovery position. Lay them on their side, on a soft surface, with their face turned to one side. This will stop them swallowing any vomit, and will keep their airway open and help prevent injury.

Stay with your child while they're having a seizure, and make a note of when the seizure started to keep track of how long it lasts. If the seizure lasts for less than five minutes, phone your GP or call the NHS 24 111 service.

If it's your child's first seizure, or if it lasts longer than five minutes, take your child to the nearest hospital as soon as possible.

While there's probably nothing seriously wrong with your child, it's best to be sure.

Don't put anything, including medication, in your child’s mouth while they're having a seizure. There's a slight chance that they might bite their tongue, although any damage isn't usually serious and will heal within a few days.

Trying to stop someone biting their tongue by placing your hand or an object in their mouth could be dangerous both for you and for them.

High temperature (fever)

Reducing a high temperature can help make your child feel more comfortable. Paracetamol and ibuprofen have been shown to be effective in reducing a high temperature. However, they won't reduce the chances of your child actually having a seizure.

Removing any unnecessary clothes and bedding will also help to lower your child’s temperature.

Aspirin should never be given to children under 16 years of age because there's a small risk that the medication could trigger a condition called Reye’s syndrome, which can cause brain and liver damage.

The use of cold sponges or fans isn't recommended for treating a high temperature. There's little evidence that they're effective, and they may cause your child discomfort. Your GP will be able to give you additional advice about treating the underlying cause of your child’s high temperature.

It's also important to prevent dehydration during a fever by making sure your child drinks plenty of fluids.

Recurring febrile seizures

About one third of children will have a febrile seizure again during a subsequent infection. This often occurs within a year of the first febrile seizure.

Recurrence is more likely if:

  • the first febrile seizure occurred before your child was 18 months old
  • there's a history of seizures or epilepsy in your family
  • before having the first seizure your child had a fever that lasted less than one hour or their temperature was less than 40C (104F) 
  • your child has multiple seizures during the same febrile episode (complex febrile seizure)
  • your child attends a day care nursery (this increases their chances of developing common childhood infections, such as the flu or chickenpox)

It's not recommended that your child is given a prescription of regular medicines to prevent further febrile seizures. This is because the adverse side effects associated with many medicines outweigh any risks of the seizures themselves.

Research has shown that the use of medication to control fever isn't likely to prevent recurrence of further febrile seizures.

However, there may be exceptional circumstances where medication to prevent recurrent febrile seizures is recommended. For example, children may need medication if they have a low threshold for having seizures during illness, particularly if the seizures are prolonged.

In this case, your child may be prescribed medications such as diazepam or lorazepam to take at the start of a fever.

Children who've had a febrile seizure following a routine vaccination (which is very rare), are no more at risk of having another seizure compared to children who've had a seizure due to another cause for fever.

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