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Febrile seizures

Introduction

Febrile seizures are a relatively common childhood condition, referring to a child having a seizure (fit) when they have a high temperature of 38ºCF (100.4ºF) or above. This is usually the result of an infection.

Frightening but harmless

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

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

What happens during a febrile seizure?

The cells in the brain, known as neurons, communicate with each other using electrical impulses. A seizure occurs when the electrical impulses become disrupted. This can cause the brain and the body to behave abnormally.

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

Types of febrile seizure

There are two main types of febrile seizure: 

  • Simple febrile seizures 
  • Complex febrile seizures

Both types are discussed in more depth below.

Simple febrile seizure

A simple febrile seizure is the most common type of febrile seizure, accounting for about 9 out of 10 cases. A simple febrile seizure is a seizure that:

  • is a tonic clonic seizure
  • does not last longer than 15 minutes
  • does not reoccur within 24 hours or during the period in which your child has an illness

Complex febrile seizure

Complex febrile seizures are less common than simple febrile seizures, accounting for 1 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

See Febrile seizures - symptoms for more information about simple and complex febrile seizures.

How common are febrile seizures?

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.

The cause of febrile seizures is unknown, although the condition appears to run in some (but not all) families. Around 1 in 4 children who are affected by febrile seizures will have a family history of the condition. However, in half of all cases, there are no obvious causes or risk factors.

Febrile seizures and epilepsy

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

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

For example, it is estimated that children with a history of simple febrile seizures have a 1 in 50 chance of developing epilepsy in later life. Children with a history of complex febrile seizures have a 1 in 20 chance of developing epilepsy in later life.

Outlook

The outlook for children with febrile seizures is excellent. Almost all children make a complete recovery, and there is not a single reported case of a child dying as the result of a febrile seizure.

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

Tests may also be needed to identify what is causing the child’s high temperature. This is particularly the case in children who are under 12 months old and in those where there is no clinically obvious source of the fever.

There is no specific treatment for febrile seizures other than treating the underlying cause of the child’s high temperature, such as using antibiotics to treat an infection.

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Symptoms

Febrile seizures often occur during the first day of a fever, which is defined as a high temperature of 38ºC (100.4ºF) or above. 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 after a mild temperature, 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. The seizure usually lasts for less than five minutes.

Following a febrile seizure, your child may be sleepy for up to an hour afterwards.

When to seek medical advice

Contact your GP as soon as possible if your child has no previous history of seizures and you think they have had a seizure. Your child may need to be referred for tests to rule out other possible causes of seizures.

If your child has previously been diagnosed as having febrile seizures, an additional diagnosis may not be required. However, it is recommended that you telephone your GP or NHS Direct (0845 4647) for advice.

Also contact your GP or NHS Direct 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

When to seek emergency medical advice

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; the rash is not always present
  • your child is having breathing difficulties
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Causes

The exact cause of febrile convulsions is unknown. Because they occur when a child has a high temperature, 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 normal 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.

Risk factors

Although the condition is poorly understood, a number of risk factors for febrile convulsions have been identified.

Family history is the most important risk factor. If a child has a first-degree relative (mother, father, sister or brother) who has a history of febrile seizures, their risk of having symptoms increases. The more relatives affected, the higher that risk, which can range from 1 in 10 to 1 in 2.

The fact that febrile seizures run in families 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 that are carried in certain genes become ‘scrambled’. This means that some of the body’s processes will not work in the normal way.

A number of potential mutations have been linked to an increased risk of febrile seizures. However, exactly how and why these mutations develop is unclear.

Associated infections

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

Other infections that are 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 for every 100,000 children who have the MMR vaccine, which protects against mumpsmeasles and rubella, 25 to 34 children will have febrile seizures.

To put this figure in context, your child has a 1 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, which protects against diphtheria, whooping cough, tetanus, polio and the haemophilus influenzae type b (Hib) virus. For every 100,000 children who receive the DTaP/IPV/Hib vaccine, 6 to 9 will have febrile seizures.

This equates to your child having a 1 in 11,000 to 16,000 chance of experiencing a febrile seizure after having the DTaP/IPV/Hib vaccine.

 

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Diagnosis

In diagnosing febrile seizures, your GP will want to identify the source of the infection. They will also want to rule out other, rarer conditions, such as meningitis, that can also cause similar symptoms.

Urine and blood tests

Your GP may want to run a series of tests, such as blood, or urine tests, to check for the signs of infection.

Sometimes it is difficult to obtain a urine sample from young children, so it may have to be done in hospital.

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 (see Febrile seizures - introduction).

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.

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 placing 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.

See A-Z topic about Lumbar puncture for more information about the procedure.

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Treatment

What to do during a seizure

During a febrile seizure, place your child 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 it will help to prevent injury. See the 'selected links' section for more information about the recovery position.

If your child is having a seizure, stay with them and make a note of how long the seizure lasts. If the seizure lasts for less than five minutes, you should phone your GP, or NHS Direct Wales, on 0845 4647.

If the seizure lasts for longer than five minutes, phone 999 and ask for an ambulance to take your child to the nearest hospital. While there is probably nothing seriously wrong with your child, it is best to be sure.

You should avoid putting anything in your child's mouth while they are having a seizure. While there is a chance that they might bite their tongue, any damage is normally not serious and will heal in a few days. Attempting to stop somebody biting their tongue, by placing your hand or an object in their mouth, could be dangerous both for you and them.

Treating the symptoms of fever

Paracetamol and ibuprofen have been shown to be effective in helping to reduce a high temperature.  Also, to help lower your child's temperature, you should remove any unnecessary clothes and bedding.

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 because 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.

Recurring febrile seizures

About one third of children will experience 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 occurred when your child was younger than 18 months old,
  • their first seizure was a complex febrile seizure,
  • you have a family history of seizures, or epilepsy, and
  • if your child attends a day nursery (as their risk of getting a common childhood infection is increased).

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. Regular medicine 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. 

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Complications

There is no evidence that simple febrile convulsions cause any lasting damage such as brain damage or learning difficulties. However, a very small number of children who have febrile convulsions go on to have epilepsy. 

Epilepsy

The risk of a child developing epilepsy after a simple febrile seizure is 1.5%. However, the risk rises to 2.5% if the child was under 12 months of age when they had their first seizure (in those who experienced multiple simple seizures).

The risk of developing epilepsy increases with each of the following factors:

  • neurological abnormalities, or a developmental delay before the onset of febrile seizures,
  • a family history of epilepsy,
  • a short duration of fever (less than one hour) before the seizure, and
  • complex seizures.

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