What Is Epilepsy?
Epilepsy is a chronic neurological disease of the brain characterised by an enduring predisposition to have epileptic seizures.
It is not one single condition and it does not produce one single type of seizure.
Around 50 million people worldwide live with epilepsy, making it one of the most common neurological diseases globally. It affects people of all ages and occurs in every part of the world.
What is an epileptic seizure?
An epileptic seizure is a temporary event produced by abnormal excessive or unusually synchronised activity within networks of brain cells.
What happens during the seizure depends on:
which brain networks are involved
how seizure activity spreads
and which functions those networks normally perform.
A seizure may temporarily affect:
consciousness
responsiveness
movement
sensation
vision
hearing
taste
speech
language
memory
thinking
emotion
behaviour
or automatic functions of the body.
WHO notes that seizures can range from extremely brief lapses of attention or muscle jerks to severe and prolonged convulsions.
This means an epileptic seizure does not always involve:
collapsing
becoming unconscious
stiffening
or shaking.
Some seizures may be obvious to an observer.
Others may be subtle or almost entirely experienced internally.
A seizure and epilepsy are not the same thing
A seizure is an event.
Epilepsy describes the enduring tendency of the brain to generate epileptic seizures.
That distinction is fundamental.
A person can experience a seizure without necessarily having epilepsy.
For example, seizures can occur during an acute medical problem affecting the brain or body.
Depending on the circumstances, this may include:
severe metabolic disturbance
an acute brain injury
infection affecting the brain
intoxication
withdrawal from certain substances
or another acute neurological illness.
These may be classified as acute symptomatic seizures rather than evidence of an enduring epileptic disorder.
So:
one seizure does not automatically mean epilepsy.
How is epilepsy defined?
The International League Against Epilepsy — ILAE — provides the internationally used practical clinical definition.
A person can be considered to have epilepsy when any one of the following applies:
Two unprovoked or reflex seizures occurring more than 24 hours apart.
Or:
One unprovoked or reflex seizure and a probability of further seizures of at least 60% over the following 10 years.
Or:
A diagnosis of an epilepsy syndrome.
This is more precise than the simplified statement:
“Epilepsy means having two seizures.”
Two unprovoked seizures remain one route to diagnosis, but they are not the only route.
Why can epilepsy sometimes be diagnosed after one seizure?
Somebody may experience one unprovoked seizure but already have other evidence showing that their risk of another seizure is sufficiently high.
The ILAE threshold is a recurrence probability similar to that following two unprovoked seizures — defined operationally as at least 60% over the next 10 years.
That risk is not guessed from the seizure alone.
Clinicians may consider evidence such as:
the clinical circumstances
EEG findings
brain imaging
an identified structural cause
and the overall neurological diagnosis.
A diagnosis after one seizure therefore does not mean:
“everyone who has one seizure has epilepsy.”
It means the evidence in that particular case supports an enduring predisposition to further epileptic seizures.
What does “unprovoked seizure” mean?
An unprovoked seizure is one that is not occurring simply as the immediate consequence of a temporary acute disturbance.
For example, there is an important difference between:
a seizure occurring because of a severe acute metabolic disturbance
and:
a spontaneous epileptic seizure occurring because the brain has an enduring tendency to generate seizures.
The distinction is sometimes straightforward.
At other times it requires specialist judgement.
This matters because the long-term risk of further seizures can differ considerably depending on why the seizure happened.
What is a reflex seizure?
A reflex seizure is an epileptic seizure reliably triggered by a particular stimulus or activity.
Examples can include seizures triggered by:
particular visual patterns
flashing light in photosensitive epilepsy
reading
certain sounds
specific cognitive activities
or other reproducible triggers in recognised reflex epilepsies.
The presence of a trigger does not automatically mean the seizure is “provoked” in the acute symptomatic sense.
The ILAE definition specifically includes reflex seizures within the diagnostic criteria for epilepsy.
What is an epilepsy syndrome?
An epilepsy syndrome is more specific than simply saying somebody has epilepsy.
A syndrome is recognised from a characteristic combination of features that may include:
seizure types
age when seizures begin
EEG findings
developmental history
cognitive features
imaging
genetics
typical triggers
and the expected course over time.
Some syndromes begin:
in infancy
in childhood
in adolescence
or at a variable age.
The diagnosis of a recognised epilepsy syndrome is itself one of the ILAE routes to an epilepsy diagnosis.
The Information Hub has a separate Epilepsy Syndrome Library because individual syndromes need much more detailed explanation than can be included here.
Epilepsy is described at several different levels
Modern epilepsy diagnosis can involve several related but different descriptions.
A clinician may identify:
the seizure type
then:
the epilepsy type
then, when possible:
the epilepsy syndrome
and:
the underlying cause.
These terms are not interchangeable.
Someone might therefore have a diagnosis that becomes increasingly specific as more information becomes available.
For example, the initial diagnosis might simply be:
epilepsy
before later investigation establishes:
the seizure classification
focal or generalised epilepsy
a recognised syndrome
or a particular structural or genetic cause.
A diagnosis can therefore be refined without meaning that the original seizures were unreal or incorrectly reported.
The seizure classification changed in 2025
The ILAE updated its international seizure classification in 2025.
The current classification has four main seizure classes:
Focal
Generalised
Unknown whether focal or generalised
Unclassified
The updated system contains 21 seizure types, compared with the much larger structure used in the 2017 classification.
Several important terminology changes were introduced.
The word “onset” was removed from the names of the four main seizure classes.
Consciousness replaced awareness as a classifier, with consciousness assessed through both awareness and responsiveness.
The previous motor versus non-motor division was replaced by:
observable manifestations
and:
non-observable manifestations.
The updated classification also encourages clinicians to describe the chronological sequence of signs and symptoms during a seizure, rather than relying only on the first recognised feature.
This Information Hub therefore uses the 2025 ILAE seizure classification rather than building its seizure information around the older 2017 terminology.
Related Information Hub page:
Focal, Generalised, Unknown and Unclassified Seizures — Understanding the 2025 ILAE Classification
Focal and generalised do not mean mild and severe
These terms describe how seizure activity is organised in the brain.
They are not severity rankings.
A focal seizure can be:
extremely subtle
disabling
prolonged
or capable of spreading into a bilateral tonic-clonic seizure.
A generalised seizure can also take very different forms.
The classification describes seizure biology and manifestation, not how seriously somebody's epilepsy affects their life.
What causes epilepsy?
There is no single cause.
WHO groups epilepsy causes broadly into:
structural
genetic
infectious
metabolic
immune
and unknown categories.
More than one category can sometimes apply.
Structural causes
A structural change in the brain may create an increased tendency to seizures.
Examples can include:
abnormalities in brain development
previous stroke
traumatic brain injury
some brain tumours
brain injury around birth
or structural abnormalities associated with particular epilepsies.
Some structural abnormalities are visible on MRI.
Others may be subtle or not visible using current imaging.
A normal MRI therefore does not rule out epilepsy.
Genetic causes
Some epilepsies have a significant genetic basis.
This does not always mean the epilepsy was inherited from a parent.
A genetic change may be:
inherited
newly occurring in the individual
or part of a more complex genetic susceptibility.
Different genetic epilepsies can behave very differently.
Some are associated with normal development.
Others form part of developmental and epileptic encephalopathies.
Related Information Hub page:
Genetic Testing and Epilepsy
Infectious causes
Brain infections can cause epilepsy.
Examples include:
encephalitis
meningitis
and neurocysticercosis.
The importance of particular infectious causes varies substantially around the world.
WHO notes that central nervous system infections remain important causes of epilepsy in many tropical and lower-resource settings.
This is one reason epilepsy needs to be understood globally rather than only through the healthcare experience of one country.
Metabolic and immune causes
Some metabolic disorders interfere with the way brain cells:
produce energy
process substances
or maintain normal electrical function.
Immune-mediated diseases can also produce epilepsy when abnormal immune activity affects the brain.
Identifying these causes can be particularly important because treatment may involve addressing the underlying disease as well as treating seizures.
Sometimes the cause remains unknown
WHO reports that the cause of epilepsy remains unknown in around half of cases globally.
“Unknown” does not mean:
the seizures are not real
the person has not been investigated properly
or epilepsy must have a psychological explanation.
It means the underlying biological cause has not currently been identified.
Medical knowledge and technology continue to change.
Some epilepsies that were once labelled unknown can now be explained through:
improved MRI
genetic testing
immune testing
or better understanding of epilepsy syndromes.
Epilepsy is not contagious
Epilepsy cannot be caught from another person.
WHO specifically identifies epilepsy as a noncommunicable disease of the brain and notes that it is not contagious.
This may sound obvious in some communities, but beliefs about contagion remain part of epilepsy-related stigma in parts of the world.
Epilepsy can begin at any age
Epilepsy affects:
babies
children
teenagers
adults
and older people.
Some epilepsy syndromes occur predominantly at particular ages.
Other causes become more common later in life.
A person therefore does not need to have had seizures since childhood to develop epilepsy.
A first epileptic seizure can occur at any age.
Epilepsy does not always remain the same
Seizure patterns may change over time.
Someone may experience changes in:
seizure type
frequency
triggers
treatment response
EEG findings
or the way seizures spread.
Children may also move through age-related epilepsy syndromes.
This is why an epilepsy diagnosis sometimes needs to be reviewed and refined rather than being treated as an unchangeable label.
Can epilepsy ever be considered resolved?
Yes.
The ILAE uses the term resolved in particular circumstances.
Epilepsy may be considered resolved when somebody:
had an age-dependent epilepsy syndrome and is now beyond the age range in which that syndrome applies;
or
has been seizure-free for at least 10 years, including at least the last 5 years without antiseizure medication.
“Resolved” does not mean medicine can guarantee that another seizure will never occur.
The ILAE explicitly distinguishes the term from an absolute guarantee of cure.
Being seizure-free and having epilepsy “resolved” are not the same thing
Someone may become seizure-free because antiseizure treatment is working.
They can still have epilepsy.
Likewise, somebody may have had no seizures for several years but continue taking antiseizure medication.
The formal ILAE definition of resolved epilepsy uses more specific criteria.
This terminology is mainly useful for accurately describing the person's current condition.
Diagnosis and treatment are separate decisions
The ILAE makes another important distinction:
diagnosing epilepsy does not automatically determine whether or how somebody should be treated.
Treatment decisions depend on individual factors including:
seizure recurrence risk
seizure type
epilepsy type
underlying cause
potential harms from further seizures
medicine risks and benefits
age
other health conditions
and the person's circumstances.
The definition tells clinicians whether the condition meets the criteria for epilepsy.
It does not prescribe one treatment for everybody.
Epilepsy is common worldwide
WHO estimates that around 50 million people worldwide live with epilepsy.
Nearly 80% live in low- and middle-income countries.
Access to epilepsy care varies enormously.
Depending on where someone lives, they may or may not have easy access to:
EEG
MRI
neurologists
epilepsy specialists
antiseizure medicines
genetic testing
surgery
or emergency care.
A global understanding of epilepsy therefore needs to separate the medical definition of the disease from the healthcare resources available in any particular country.
The most important distinction
Epilepsy should not be defined by how dramatic a seizure looks.
A person does not need to:
collapse
shake
lose consciousness
bite their tongue
or require emergency treatment
for a seizure to be epileptic.
Nor does one seizure automatically establish epilepsy.
Epilepsy describes an enduring predisposition of the brain to generate epileptic seizures.
The diagnosis can be established through:
recurrent unprovoked or reflex seizures
one seizure accompanied by a sufficiently high risk of recurrence
or diagnosis of an epilepsy syndrome.
What those seizures look like can vary enormously because different seizures involve different brain networks.
That is why the question:
“What does an epileptic seizure look like?”
does not have one answer.
And it is why modern epilepsy diagnosis goes beyond simply deciding whether somebody has epilepsy.
It aims to establish:
what seizure type they experience
what type of epilepsy they have
whether they have a recognised syndrome
and, when possible, what is causing it.
Sources and further reading
International League Against Epilepsy — A Practical Clinical Definition of Epilepsy.
The ILAE clinical definition allows epilepsy to be diagnosed after two unprovoked or reflex seizures more than 24 hours apart, after one such seizure when the estimated 10-year recurrence risk is at least 60%, or when an epilepsy syndrome is diagnosed. It also defines when epilepsy may be considered resolved.
International League Against Epilepsy — Updated Classification of Epileptic Seizures, 2025.
The current international classification uses four main seizure classes — focal, generalised, unknown whether focal or generalised, and unclassified — and contains 21 seizure types. The update also introduced changes including the use of consciousness rather than awareness and greater emphasis on the chronological sequence of seizure manifestations.
World Health Organization — Epilepsy.
WHO describes epilepsy as a chronic noncommunicable disease of the brain affecting around 50 million people worldwide and provides international information on seizure manifestations, causes, treatment gaps and global burden.
Information reviewed: September 2026.
This page provides general educational information for an international audience. Epilepsy diagnosis requires clinical assessment, and available investigations and specialist services vary between countries.
