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

Some researchers speculate 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 the condition is poorly understood, family history is thought to increase the risk of febrile seizures. 

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 that risk.

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

Associated infections

The majority of cases of febrile convulsions occur when a child has a high temperature caused by an infection. The three most common types of infection associated with febrile convulsions are:

• viral infections, such as chickenpox and flu
• middle ear infections
• tonsillitis 

Other infections associated with febrile seizures (listed in order of most to least common) are:

• 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 (an infection of the lungs) and bronchitis (an infection of the airways that supply the lungs)

Febrile seizures and vaccinations

In rare cases, febrile seizures can occur after a child has a vaccination. Research has shown that your child has a 1 in 3,000 to 4,000 chance of having a febrile seizure after having the MMR vaccine, which protects against mumps, measles and rubella.

The risks are even lower with the DTaP/IPV/Hib vaccine, which protects against diphtheria, whooping cough, tetanus, polio and the haemophilus influenzae type b (Hib) virus. Your child has a 1 in 11,000 to 16,000 chance of experiencing a febrile seizure after having the DTaP/IPV/Hib vaccine. 

Febrile seizures can often be diagnosed from a description of what happened, although further tests may be needed.

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

If a febrile seizure is suspected, tests may be carried out to identify the source of the infection and rule out rarer conditions, such as meningitis, which can cause some similar symptoms.

Urine and blood tests

Your GP may want to take a blood or urine sample to be tested for signs of infection. Sometimes it is 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 do not have a high temperature or their seizures do not follow the normal pattern.

Further testing and observation in hospital is also usually recommended if your child is having complex febrile seizures (read the introduction to febrile seizures for more information on the types of seizure).

Your child may have other tests, including:

• an electroencephalogram
• lumbar puncture (particularly if your child is less than 12 months old)

These are briefly explained below.

Electroencephalogram

An electroencephalogram (EEG) measures the electrical activity of your child’s brain 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.

Read more about electroencephalograms.

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.

The sample of CSF is obtained by inserting a hollow needle into the base of your child’s spine and drawing out a few millimetres of fluid. During the procedure, local anaesthetic will be used to numb your child’s back so that they feel no pain.

A lumbar puncture is an effective method of determining whether your child has an infection of the brain or nervous system.

Read more about lumbar punctures.

A febrile seizure is a fit that occurs when a child has a fever. It’s a relatively common childhood condition and not serious in most cases.

Febrile seizures are also sometimes called febrile convulsions.

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

Read more about the symptoms of febrile seizures.

Frightening but harmless

Seeing a child having a seizure, particularly if they have no previous history of fits, can be frightening and distressing for the parents.

Many parents say they were convinced that their child was going to die. However, while febrile seizures may be frightening, most are harmless and do not pose a threat to a child’s health.

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. It will keep their airway open and help to prevent injury.

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

If it is your child’s first seizure, or it lasts longer than five minutes, take them to the nearest hospital as soon as possible or call 999 for an ambulance. While it is unlikely that there is anything seriously wrong, it is 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 NHS 111 for advice.

Try not to put anything, including medication, in your child’s mouth during a seizure as there is a slight chance that they might bite their tongue.

Almost all children make a complete recovery, and there is not a single reported case of a child dying as the direct result of 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 8 out of 10 cases. A simple febrile seizure is a fit that:

• is a tonic clonic seizure
• does not last longer than 15 minutes
• does not reoccur during the period in which your child has an illness

Complex febrile seizure

Complex febrile seizures are less common, accounting for 2 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 period in which they have an illness
• your child does not fully recover from the seizure within one hour

Why do febrile seizures happen?

The cause of febrile seizures is unknown, although it is linked to the start of a fever – a high temperature of 38ºC (100.4ºF) or above.

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

• chickenpox
• flu (influenza)
• middle ear infections (otitis media)
• tonsillitis

There may also be a genetic link to febrile seizures, as 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.

Who is affected?

Febrile seizures are quite common. An estimated 1 in 20 children will have at least one febrile seizure at some point. Most febrile seizures occur between the ages of six months and three years. The average age is 18 months.

Complications

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

Recent research has reported initial findings that 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 has not been proven and SUDC is incredibly rare, affecting only around 1 in 100,000 children (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.

The Map of Medicine is used by doctors throughout the NHS to determine the best treatment options for their patients. NHS Choices offers everyone in England exclusive and free access to this cutting-edge internet resource, which lets you see exactly what your doctor sees.

The information in the Map has been approved by the UK’s leading clinical experts, is based on the best available clinical evidence, and is continually updated. To take advantage of this unique resource go to:

Map of Medicine: febrile seizures

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 38ºC (100.4ºF) or above. 

However, there appears to be no direct connection between the extent of your child’s fever and the start of a seizure. Seizures can develop even if your child has a mild fever, and may not develop at all with an extremely high temperature.

Simple febrile seizures can sometimes occur at the time of a rapid rise in temperature. In these cases, it is common to only realise that your child is ill when they have the seizure.

Alternatively, seizures can occur as your child’s temperature drops from a previously high level.

During simple febrile seizures, your child’s body will become stiff and their arms and legs will begin to twitch. They will lose consciousness and they may wet or soil themselves. Your child may also vomit and foam at the mouth and their eyes may roll back.

The seizure usually lasts for less than five minutes.

Following a febrile 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.

Seeking medical advice

If your child has previously been diagnosed as having febrile seizures, you may not need to seek emergency care. However, it is recommended that you telephone your GP or call NHS 111 for advice.

Also, contact your GP or NHS 111 if your child shows signs and symptoms of dehydration (a lack of fluid in their body). The signs of dehydration are:

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

Emergency advice

You should take your child to the nearest hospital as soon as possible if they have no previous history of seizures and you think they have had one.

Although very rare, a seizure can sometimes be a sign of a more serious illness, such as meningitis, which requires emergency medical treatment.

Dial 999 immediately to request an ambulance if your child has any of the symptoms below:

• your child is having a seizure that is lasting longer than five minutes and showing no signs of stopping
• your child has a blotchy red rash that does not fade or change colour when you place a glass against it (such a rash is not always present)
• your child is having breathing difficulties

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. It will keep their airway open and help to prevent injury.

Read more about the recovery position.

If your child is having a seizure, stay with them and make a note of when the seizure started in order to keep track of how long it lasts. If the seizure lasts for less than five minutes, phone your GP or call NHS 111.

If it is your child’s first seizure, or it lasts longer than five minutes, take your child to the nearest hospital as soon as possible. While there is probably nothing seriously wrong with your child, it is best to be sure.

Avoid putting anything, including medication, in your child’s mouth while they are having a seizure. There is a slight chance that they might bite their tongue, but any damage is not 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 for you and for them.

High temperature (fever)

Reducing a high temperature can help to make your child feel more comfortable, but doesn’t affect the chances of a seizure.

Paracetamol and ibuprofen have been shown to be effective in reducing a high temperature. 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 old. There is 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 is not recommended for treating a high temperature. There is little evidence that they are effective, and they may cause your child discomfort. Your GP can give you additional advice about treating the underlying cause of your child’s high temperature.

It is also important to prevent dehydration during a fever by ensuring that 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 episode.

Recurrence is more likely if:

• the first febrile seizure happened when your child was younger than 18 months old
• your child’s first seizure was a complex febrile seizure (read the introduction to febrile seizures for more information on the types of seizure)
• you have a family history of seizures or epilepsy
• your child attends a day nursery – this increases their risk of developing a common childhood infection

It is 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 that are associated with the seizures themselves.

Research has shown that the use of medication to control fever is not likely to prevent recurrence of further febrile seizures.

However, there may be exceptional circumstances in which medication to prevent recurrent febrile seizures is recommended. For example, children may need medication if they have a low threshold for having seizures during febrile 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. This is to prevent seizures or, more commonly, to take if a seizure lasts longer than five minutes if this has happened before.

There is no evidence that vaccinations increase the risk of recurring febrile seizures.