What Causes Epilepsy
There is no single cause of epilepsy.
Epilepsy can develop because of:
an alteration in brain structure
a genetic change or genetic susceptibility
an infection
a metabolic disorder
an immune-mediated disease
or another biological process that creates an enduring tendency for the brain to generate epileptic seizures.
For many people, however, the underlying cause cannot currently be identified.
The International League Against Epilepsy — ILAE — groups epilepsy aetiology into six principal categories:
structural
genetic
infectious
metabolic
immune
unknown
These categories are not mutually exclusive. The same person's epilepsy may belong to more than one category.
What does “aetiology” mean?
Aetiology means the underlying cause or disease mechanism.
When clinicians ask about the aetiology of epilepsy, they are asking:
Why has this person's brain developed an enduring tendency to generate epileptic seizures?
That is different from asking:
What triggered today's seizure?
For example, lack of sleep might make a seizure more likely in somebody who already has epilepsy.
But lack of sleep is not necessarily the biological cause of their epilepsy.
Related Information Hub page:
Seizure Triggers vs Seizure Causes — What's the Difference?
Why does finding the cause matter?
The cause is not simply an extra label.
Identifying it may affect:
prognosis
treatment choices
suitability for epilepsy surgery
genetic counselling
investigation of other organs or body systems
screening of relatives in selected conditions
and whether treatment can target the underlying disease as well as the seizures.
The ILAE deliberately incorporated aetiology into epilepsy classification because understanding the cause can have significant therapeutic implications.
More than one cause category can apply
The six ILAE categories should not be thought of as separate boxes where every person must fit into exactly one.
For example, tuberous sclerosis complex is caused by genetic changes but can also produce structural abnormalities in the brain associated with epilepsy.
That person's epilepsy can therefore correctly be described as both:
genetic
and:
structural.
The ILAE specifically uses tuberous sclerosis as an example of why the categories can overlap.
The categories are also not ranked.
Structural is not more important than genetic, and genetic is not more serious than unknown.
Different labels describe different parts of the underlying biology.
Structural causes
A structural aetiology means there is an abnormality of brain structure that is reasonably believed to be responsible for the epilepsy.
The abnormality may be:
present from early brain development
caused by a genetic disorder
or acquired later because of disease or injury.
The important point is not simply that an MRI abnormality exists.
The structural finding needs to fit the person's epilepsy closely enough for clinicians to reasonably infer that it is related to the seizures.
Examples of structural causes
Structural causes can include:
focal cortical dysplasia
hippocampal sclerosis
abnormalities of cortical development
brain injury associated with stroke
traumatic brain injury
some brain tumours
vascular abnormalities
damage following infection
and some forms of brain injury occurring before, during or around birth.
WHO includes severe head injury, stroke, congenital brain abnormalities, brain tumours and prenatal or perinatal brain injury among recognised causes of epilepsy.
Structural does not necessarily mean acquired
It is easy to assume:
structural = something that damaged the brain later.
That is not correct.
Some structural abnormalities develop because the brain formed differently.
Others have a genetic origin.
The ILAE gives malformations of cortical development as an important example: some arise from genetic causes, while others may result from acquired processes such as congenital infection.
So an epilepsy can simultaneously be:
structural and genetic
or:
structural and infectious.
Focal cortical dysplasia
Focal cortical dysplasia — FCD is an abnormality in the development and organisation of part of the cerebral cortex.
It is an important structural cause of focal epilepsy.
Some forms are extremely subtle and may be difficult to recognise even on specialist MRI.
FCD is particularly important in epilepsy-surgery assessment because, in selected people, identifying and treating the epileptogenic region can provide a route to substantially improved seizure control.
Focal cortical dysplasia will have its own detailed Information Hub page under The Brain & Seizure Networks rather than being expanded further here.
Hippocampal sclerosis
Hippocampal sclerosis refers to characteristic neuronal loss and scarring involving the hippocampus.
It is strongly associated with some forms of mesial temporal lobe epilepsy.
The relationship between hippocampal sclerosis and epilepsy can be complex, and this condition warrants its own page rather than being reduced to simply:
“a scar that causes seizures.”
Planned related Information Hub page:
Hippocampal Sclerosis
Stroke and epilepsy
Stroke is an important acquired cause of epilepsy, particularly in adults and older people.
A stroke can damage brain tissue and create a region or network capable of generating later unprovoked seizures.
WHO includes stroke among the major recognised causes of epilepsy worldwide.
Importantly, a seizure occurring during the acute phase of a stroke and epilepsy developing later after a stroke are not necessarily the same clinical situation.
The distinction between an acute symptomatic seizure and later post-stroke epilepsy depends on timing and recurrence risk.
Planned related Information Hub page:
Stroke and Post-Stroke Epilepsy
Traumatic brain injury
Brain trauma can also create a structural predisposition to epilepsy.
Risk is influenced by factors such as:
severity of injury
location
bleeding
penetrating injury
and the extent of brain tissue damage.
WHO identifies severe head injury as an established cause of epilepsy and also notes that preventing traumatic brain injury is one important way of preventing some cases of epilepsy.
Not everybody who experiences a head injury will develop epilepsy.
Brain tumours
Some brain tumours can cause epilepsy.
In some people, a seizure may be one of the first signs leading to identification of the tumour.
The likelihood of seizures varies considerably according to:
tumour type
location
interaction with surrounding cortex
and other biological characteristics.
WHO includes brain tumours among recognised structural causes of epilepsy.
A tumour-associated seizure does not tell clinicians by itself whether a tumour is:
benign
malignant
slow-growing
or aggressive.
Those are separate questions.
Brain injury around birth
Epilepsy can sometimes result from brain injury occurring:
before birth
during birth
or shortly afterwards.
Possible mechanisms include:
reduced oxygen delivery
cerebral injury
infection
stroke
or abnormalities of brain development.
WHO includes prenatal and perinatal brain injury among important causes of epilepsy worldwide.
The cause may ultimately be classified as:
structural
infectious
genetic
metabolic
or a combination
depending on what produced the brain injury.
Genetic causes
A genetic aetiology means epilepsy results directly from a known or presumed genetic factor in which seizures are a central part of the disorder.
This does not mean every genetic epilepsy is inherited from a parent.
Genetics is much broader than inheritance.
Genetic does not necessarily mean inherited
A genetic change may be:
inherited from one or both parents
newly occurring in the affected person
part of a complex combination of many genetic variants
or presumed from strong evidence about a particular epilepsy syndrome even when one individual causative variant has not been identified.
A newly occurring genetic alteration is often described as de novo.
This is why:
“Nobody else in my family has epilepsy”
does not rule out a genetic cause.
Some genetic epilepsies involve one major gene
In some conditions, alteration of a particular gene has a major role.
Examples include genetic epilepsies associated with genes such as:
SCN1A
KCNQ2
STXBP1
CDKL5
PCDH19
and many others.
But this should not create the impression that epilepsy can always be explained by finding one faulty gene.
The genetics of epilepsy ranges from relatively clear single-gene disorders to highly complex susceptibility involving many genetic variants.
Modern genomic research has shown that genetics contributes to epilepsy more widely than was once appreciated.
Some common epilepsies have complex genetic architecture
Conditions such as some generalised epilepsies can have strong genetic influences without following a simple:
parent has gene → child inherits disease
pattern.
Multiple genetic variants may contribute small amounts of risk.
Environmental and developmental factors may also interact with that susceptibility.
This is one reason a person can have a strongly genetic epilepsy despite having:
no affected parent
no affected siblings
and no obvious family history.
A genetic cause may also produce structural epilepsy
Genes control how the brain develops.
A genetic alteration can therefore produce:
a malformation of cortical development
a tumour-predisposition syndrome
or another structural change
that subsequently contributes to epilepsy.
In such cases both:
genetic
and:
structural
may be accurate descriptions.
The ILAE emphasises that these categories are designed to overlap when biology overlaps.
Genetics can affect more than seizures
Some genetic conditions primarily produce epilepsy.
Others affect several aspects of neurological development or other organs.
Depending on the condition, genetic information may help explain:
developmental differences
movement disorders
behavioural or cognitive features
cardiac problems
metabolic abnormalities
or other medical findings.
But this varies greatly between disorders.
Related Information Hub page:
Genetic Testing and Epilepsy
Infectious causes
An infectious aetiology means epilepsy has resulted from a known infection affecting the nervous system.
This is a particularly important category when epilepsy is considered globally.
The ILAE lists examples including:
neurocysticercosis
tuberculosis
HIV-associated disease
cerebral malaria
cerebral toxoplasmosis
congenital cytomegalovirus
and other central nervous system infections.
The importance of individual infections varies enormously between regions.
Infection during a seizure is not automatically infectious epilepsy
This distinction is essential.
Someone can have an epileptic seizure during an acute infection without necessarily developing epilepsy.
For example, an acute episode of:
meningitis
encephalitis
or severe systemic illness
may provoke seizures while the illness is active.
An infectious epilepsy, in the ILAE sense, refers to epilepsy resulting from the infection, including cases where an infection leaves an enduring epileptogenic effect after the acute illness has ended.
So:
acute seizure during infection
and:
epilepsy caused by previous infection
are related but different concepts.
Neurocysticercosis
One of the most important causes to understand internationally is neurocysticercosis.
It occurs when larvae of the parasite Taenia solium infect the central nervous system.
It can cause:
seizures
focal neurological problems
hydrocephalus
raised intracranial pressure
and epilepsy.
WHO describes neurocysticercosis as one of the leading preventable causes of epilepsy worldwide and estimates that it may account for around 30% of epilepsy cases in some endemic areas.
It is particularly important in parts of:
Latin America
sub-Saharan Africa
South Asia
and South-East Asia.
This is an example of why a genuinely global epilepsy resource cannot focus only on the causes most commonly seen in high-income countries.
Infections can leave structural damage
The infectious and structural categories frequently overlap.
An infection may produce:
inflammation
scarring
calcification
tissue destruction
or abnormalities of brain development.
The immediate cause may therefore be infectious, while the lasting epileptogenic substrate is structural.
Both labels may be useful.
Congenital infections
Infections occurring during pregnancy can affect the developing brain.
The ILAE identifies congenital infections such as:
cytomegalovirus
and Zika virus
among infectious causes that can be associated with epilepsy.
The mechanism may involve both:
infection
and abnormal brain development.
Again, more than one aetiological category may apply.
Metabolic causes
A metabolic aetiology means epilepsy results directly from a defined disorder affecting the body's biochemical processes.
Cells require carefully regulated systems for:
producing energy
processing nutrients
maintaining electrolytes
synthesising neurotransmitters
and performing many other chemical functions.
Some metabolic diseases interfere with these processes in ways that create persistent susceptibility to seizures.
The ILAE includes metabolic disorders as a distinct aetiological category because identifying the metabolic defect can have major treatment implications.
Metabolic epilepsy is not the same as a seizure caused by temporary low blood sugar
This distinction is similar to infectious epilepsy.
A severe temporary metabolic disturbance such as:
profound hypoglycaemia
severe sodium disturbance
or another acute biochemical abnormality
can provoke an acute symptomatic seizure.
That does not necessarily mean the person has a chronic metabolic epilepsy.
A metabolic epilepsy refers to a recognised metabolic disorder that creates an enduring epileptic predisposition.
Examples of metabolic epilepsies
The ILAE has identified examples including:
aminoacidopathies
porphyria
pyridoxine-dependent epilepsy
and other defined biochemical disorders.
The field continues to expand as new metabolic and genetic mechanisms are recognised.
Some metabolic epilepsies are especially important to diagnose early because specific therapy may substantially alter the neurological outcome.
Genetic and metabolic causes often overlap
Many metabolic pathways are controlled by genes.
A genetic alteration may therefore cause a metabolic disorder which in turn causes epilepsy.
Such epilepsy may appropriately be classified as both:
genetic
and:
metabolic.
This again illustrates why the ILAE categories are not intended as mutually exclusive boxes.
Some metabolic epilepsies have targeted treatments
This is one reason identifying the cause matters.
For certain metabolic disorders, treatment may include:
a specific vitamin
dietary therapy
replacement of a missing substrate
avoiding a harmful substance
or another disease-specific intervention.
The precise treatment belongs to the individual disorder and should not be generalised across metabolic epilepsies.
The important point is that sometimes identifying the aetiology changes care far beyond simply choosing an antiseizure medicine.
Immune causes
An immune aetiology means epilepsy results directly from an immune-mediated disorder affecting the brain.
The immune system normally protects the body.
In some diseases, however, abnormal immune activity targets:
receptors
proteins
cells
or other structures within the nervous system.
The resulting inflammation can produce seizures and, in some cases, persistent epilepsy.
The ILAE created a separate immune category because recognising these diseases can have major treatment implications.
Autoimmune encephalitis
One important group involves autoimmune encephalitis.
Examples include disorders associated with antibodies such as:
NMDA receptor antibodies
LGI1 antibodies
CASPR2 antibodies
and others.
Seizures may occur alongside features such as:
rapidly developing memory problems
behavioural or psychiatric changes
altered consciousness
movement abnormalities
language disturbance
autonomic symptoms
or other neurological changes.
But these features vary depending on the underlying immune disorder.
The ILAE specifically cites anti-NMDA receptor and anti-LGI1 encephalitis as examples of immune aetiology.
An autoimmune seizure is not automatically chronic epilepsy
During active autoimmune encephalitis, somebody may experience acute symptomatic seizures.
Whether they later have an enduring epileptic predisposition depends on:
the particular disease
response to treatment
persistent structural injury
and other individual factors.
So, as with infections and metabolic disturbances, clinicians distinguish between:
seizures occurring during an active acute illness
and:
epilepsy resulting from that illness.
Related Information Hub page:
Blood Tests, Lumbar Puncture and Antibody Testing in Epilepsy
Unknown cause
Sometimes no definite cause can be identified.
The ILAE calls this:
unknown aetiology.
WHO estimates that the underlying cause remains unknown in approximately half of epilepsy cases globally.
This is a legitimate medical classification.
It does not mean:
the epilepsy is psychological
the seizures are less real
nothing biological is happening
or clinicians have proved there is no underlying cause.
It means the cause has not yet been established.
“Unknown” may change over time
An epilepsy described as unknown today may later be explained by:
improved MRI
identification of a genetic variant
discovery of an immune mechanism
recognition of a particular syndrome
new metabolic testing
or advances that do not yet exist.
The history of epilepsy medicine contains many disorders that moved from:
unknown
to:
biologically explained
as scientific knowledge advanced.
Access to healthcare affects how often a cause is found
The ability to identify an aetiology depends partly on which investigations are available.
The ILAE specifically notes that the extent to which a cause can be established varies between healthcare settings and countries.
A person who cannot access:
MRI
genetic testing
specialist neuroimaging
metabolic investigations
antibody testing
or expert epilepsy care
may remain classified as unknown for reasons very different from somebody who has undergone extensive specialist investigation.
This is an important global limitation.
Unknown does not mean idiopathic in exactly the same way
Older epilepsy terminology sometimes used words such as:
idiopathic
when there was no obvious acquired structural cause and a genetic basis was suspected.
Modern classification increasingly favours describing:
epilepsy type
syndrome
and actual or presumed aetiology
more explicitly.
So old medical records may use terms that do not map perfectly onto current classifications.
The word unknown simply means that the underlying aetiology has not been established.
Where does neurodegeneration fit?
The formal ILAE epilepsy classification uses the six categories:
structural
genetic
infectious
metabolic
immune
unknown.
However, later specialist reviews and ILAE educational material also discuss neurodegenerative disorders as an increasingly important group of epilepsy aetiologies, particularly as populations age.
Neurodegenerative disease can involve several interacting mechanisms, so it has not simply replaced the established six-category framework.
Examples of neurological diseases associated with increased seizure risk include some:
dementias
progressive neurological disorders
and other degenerative brain diseases.
This area is continuing to develop.
Why age can influence likely causes
Epilepsy can begin at any age, but the distribution of underlying causes changes across the lifespan.
In infancy and childhood, clinicians may particularly consider:
genetic disorders
developmental brain abnormalities
metabolic conditions
perinatal injury
and infections.
In adults, possible causes increasingly include:
acquired brain injury
tumour
infection
immune disorders
and genetic conditions that first become apparent later.
In older adults, causes such as:
stroke
structural brain disease
and neurodegenerative conditions
become increasingly relevant.
This does not mean age alone determines the cause.
It changes the probabilities clinicians consider.
Some causes are potentially preventable
WHO estimates that around 25% of epilepsy cases may be preventable.
This does not mean a quarter of people with epilepsy caused their condition or failed to prevent it.
Prevention is largely about public health, including reducing conditions that can injure the brain.
Examples include:
preventing severe head injuries
improving pregnancy and birth care
preventing stroke
controlling central nervous system infections
and reducing exposure to preventable infections such as neurocysticercosis.
Many causes of epilepsy are not preventable with current knowledge.
Preventing head injury
WHO identifies prevention of traumatic brain injury as an important way to reduce post-traumatic epilepsy.
Population measures can include:
road safety
fall prevention
workplace protection
and appropriate sports-safety measures.
This is population-level prevention.
It does not mean every head injury causes epilepsy or that every later epilepsy could have been avoided.
Preventing stroke
Because stroke is an important cause of acquired epilepsy, reducing stroke risk can also prevent some cases of epilepsy.
WHO highlights measures addressing:
high blood pressure
diabetes
tobacco use
obesity
and excessive alcohol consumption
as part of stroke-related epilepsy prevention.
Again, this is a public-health principle rather than an explanation for any one individual's epilepsy.
Preventing infectious epilepsy
In some parts of the world, preventing neurological infection could substantially reduce epilepsy incidence.
WHO highlights:
parasite control
sanitation
health education
and prevention of central nervous system infection
as important measures.
Neurocysticercosis is particularly important because it remains one of the leading preventable causes of epilepsy globally.
Why causes differ around the world
The distribution of epilepsy aetiologies is not identical between countries.
WHO reports higher epilepsy incidence in many low- and middle-income countries and identifies contributing factors including:
endemic infections such as neurocysticercosis and malaria
birth-related brain injury
road traffic injuries
differences in preventive healthcare
and differences in access to medical services.
This makes epilepsy a genuinely global neurological condition whose causes are partly shaped by:
biology
environment
infection
injury
healthcare
and socioeconomic conditions.
Cause and seizure type are different things
The same broad cause can produce different seizure types.
For example, a structural abnormality may produce:
focal preserved-consciousness seizures
focal impaired-consciousness seizures
or focal seizures that progress to bilateral tonic-clonic seizures.
Conversely, people with similar seizure appearances may have completely different underlying causes.
So:
seizure type describes the seizure
while:
aetiology explains why the epilepsy exists.
These are different levels of the diagnosis.
Cause and epilepsy syndrome are also different
Some epilepsy syndromes have:
strong genetic causes
characteristic structural abnormalities
or known metabolic mechanisms.
Others remain biologically heterogeneous.
Naming a syndrome therefore does not always provide a complete molecular or structural explanation.
Likewise, identifying a cause does not automatically mean the person has a particular epilepsy syndrome.
Cause and trigger are different
This distinction is worth reinforcing.
Suppose a person has epilepsy caused by a cortical malformation.
Their seizures may become more likely after:
missed medication
insufficient sleep
illness
or another trigger.
The malformation remains the underlying cause.
Sleep loss or missed medication may be a trigger.
Avoiding the trigger does not remove the underlying epilepsy.
Cause and seizure precipitant can coexist
An individual seizure can therefore be understood at several levels.
For example:
Underlying epilepsy cause: focal cortical dysplasia.
Current epilepsy: focal epilepsy.
Immediate precipitating factor: missed medication and severe sleep loss.
Event: focal seizure progressing to bilateral tonic-clonic seizure.
All four statements can be true at the same time.
This is why epilepsy terminology can seem complicated: different terms are answering different questions.
Finding a cause does not necessarily mean it can be removed
Sometimes identifying the cause leads to a specific intervention.
Sometimes it does not.
A known cause might:
be surgically treatable
have a targeted metabolic therapy
require immune treatment
have genetic counselling implications
or primarily provide information about prognosis.
In other situations, doctors can identify the cause but cannot directly reverse it.
Treatment may therefore still focus mainly on controlling seizures and reducing their consequences.
Not finding a cause does not prevent treatment
Someone does not need a proven genetic mutation or visible MRI lesion before their epilepsy can be treated.
Many people have well-established epilepsy despite an unknown aetiology.
Treatment is based on the entire clinical picture, including:
seizure type
epilepsy type
syndrome where identifiable
and individual circumstances.
The underlying cause is important, but it is only one component of epilepsy care.
Causes can be discovered years after epilepsy begins
A person's original records may say:
“cause unknown.”
Years later:
improved MRI may reveal a subtle structural lesion
genetic testing may identify a pathogenic variant
a syndrome may become recognised
or new scientific discoveries may explain a previously unknown condition.
That does not mean the epilepsy suddenly acquired a cause.
It means medicine became able to identify one.
Why keeping old records can matter
Old:
MRI scans
EEG reports
hospital letters
developmental records
family history
and pathology reports
may become valuable when a diagnosis is reconsidered years later.
New specialists may interpret old findings differently in light of:
improved knowledge
new technology
or a newly recognised syndrome.
This is particularly relevant when epilepsy remains uncontrolled.
The most important message
There is no single cause of epilepsy.
The ILAE currently organises epilepsy aetiology into six principal categories:
structural
genetic
infectious
metabolic
immune
and:
unknown.
These categories can overlap.
A person's epilepsy might be both:
genetic and structural
infectious and structural
genetic and metabolic
or involve another combination.
Structural causes include conditions such as:
stroke
traumatic brain injury
developmental abnormalities
hippocampal sclerosis
focal cortical dysplasia
and some brain tumours.
Genetic epilepsy does not necessarily mean inherited epilepsy.
Infectious causes remain particularly important globally, with neurocysticercosis contributing substantially to epilepsy in some endemic regions.
Metabolic epilepsies result from specific biochemical disorders.
Immune epilepsies result from abnormal immune processes affecting the nervous system.
And for many people, the cause remains unknown.
WHO currently estimates that approximately 50% of epilepsy cases worldwide have no identified cause.
Unknown does not mean unreal.
It means:
medicine has not yet identified the underlying mechanism.
Finding the cause can influence:
treatment
prognosis
counselling
surgical assessment
and sometimes treatment of the underlying disease itself.
But epilepsy remains real and treatable even when its cause cannot be found.
Sources and further reading
International League Against Epilepsy — Classification of the Epilepsies.
The ILAE classification incorporates aetiology throughout epilepsy diagnosis and recognises six principal groups: structural, genetic, infectious, metabolic, immune and unknown. More than one category can apply to the same person.
Scheffer IE and colleagues — ILAE Classification of the Epilepsies: Position Paper, Epilepsia.
The original ILAE position paper explains the biological basis and clinical meaning of each aetiological category and why aetiology can have important treatment implications.
World Health Organization — Epilepsy.
WHO provides current worldwide information on epilepsy causes and estimates that the cause remains unknown in around half of cases globally. It also highlights stroke, head injury, brain infection, congenital abnormalities, genetic syndromes and brain tumours as recognised causes.
Sander and colleagues — The Aetiologies of Epilepsy.
This educational review discusses structural, genetic, infectious, metabolic and immune causes and additionally considers the growing importance of neurodegenerative disease in epilepsy.
World Health Organization — Taeniasis/Cysticercosis.
WHO identifies neurocysticercosis as one of the most important preventable causes of epilepsy worldwide and estimates that it may account for approximately 30% of epilepsy in some endemic regions.
World Health Organization — Epilepsy prevention.
WHO estimates that around one quarter of epilepsy cases may be preventable through measures including prevention of brain injury, improved perinatal care, stroke prevention and control of central nervous system infections.
Information reviewed: September 2026.
This page provides general educational information for an international audience. The causes of epilepsy, available investigations and access to specialist services vary substantially between countries and individuals.
