Epilepsy has no single cause. It can result from genetic mutations, brain injuries, infections, immune system problems, metabolic disorders, or structural abnormalities in the brain. In nearly half of all cases worldwide (about 47%), the cause is either genetic or simply unknown. The condition is diagnosed after a person has two or more unprovoked seizures separated by at least 24 hours, which distinguishes it from one-time seizures triggered by temporary conditions like low blood sugar or high fever.
Seizures vs. Epilepsy
Having a seizure doesn’t automatically mean you have epilepsy. Many people experience a single seizure at some point in their lives without ever having another. Seizures can be provoked by temporary factors: a sharp drop or spike in blood sugar, changes in blood sodium or calcium levels, kidney or liver problems, eclampsia during pregnancy, or high fevers in children. These are considered provoked seizures, and once the trigger is resolved, the seizures typically stop.
Epilepsy, by contrast, involves a lasting tendency of the brain to produce unprovoked seizures. Unless there’s a history of brain damage, a family history of epilepsy, or other neurological abnormalities, a single seizure usually isn’t followed by more.
Genetic Causes
Some forms of epilepsy are directly caused by mutations in genes that control how brain cells communicate. One of the best-studied examples involves the SCN1A gene, which provides instructions for building a sodium channel in nerve cells. Hundreds of mutations in this gene have been identified, and they cause a range of seizure disorders from relatively mild febrile seizures in infancy to severe conditions like Dravet syndrome, which produces prolonged, hard-to-control seizures.
These mutations work in different ways. Some change the structure of the sodium channel, others produce a nonfunctional version of it, and still others reduce how many channels each nerve cell makes. The end result is the same: the channels can’t properly regulate the flow of sodium ions into neurons, which disrupts the electrical signaling that brain cells depend on.
Genetic epilepsy doesn’t always follow a clean inheritance pattern. In some families, multiple members carry the same mutation but experience very different seizure types or severity. In other cases, a genetic mutation arises spontaneously in the child rather than being inherited from either parent.
Structural Brain Abnormalities
Physical changes to the brain’s structure are a major category of epilepsy causes. These can be something a person is born with, like malformations in how the brain’s outer layer (the cortex) developed, or something acquired later in life through injury, stroke, or a tumor. Common structural causes include focal cortical dysplasia (a patch of abnormally organized brain tissue), hippocampal sclerosis (scarring in a part of the brain involved in memory), vascular malformations, and damage from oxygen deprivation at birth.
Detecting these abnormalities often requires specialized MRI scans. Standard brain imaging can miss subtle malformations, so epilepsy-specific imaging protocols are used to look for things like small areas of cortical dysplasia that wouldn’t show up on a routine scan. When a structural cause is found, it sometimes opens the door to surgical treatment, since removing or disconnecting the abnormal area can reduce or eliminate seizures.
Traumatic Brain Injury
Head injuries carry a measurable risk of epilepsy that varies dramatically depending on the type and severity of injury. A large registry-based study found that the overall 10-year risk of developing epilepsy after any traumatic brain injury is about 4%. But the numbers diverge sharply by injury type: focal injuries to the brain tissue itself carry a 12.9% risk, diffuse brain injuries about 8.1%, and mild traumatic brain injuries around 2.6%.
The timing is unpredictable. In the study population, the median time from injury to first epilepsy diagnosis was one year, but some people didn’t develop seizures until 17 years after their injury. This long window means that someone who had a serious head injury decades ago and never had a seizure could still develop post-traumatic epilepsy, though the risk decreases over time. Adults over 35 who develop epilepsy for the first time often have stroke as the underlying cause, making it the leading trigger in that age group.
Infections
Brain infections are likely the most common cause of epilepsy worldwide, particularly in lower-income countries. The infection damages brain tissue, and the resulting scarring or structural changes create the conditions for ongoing seizures even after the infection itself has been treated.
The list of infections linked to epilepsy is long. Neurocysticercosis, a parasitic infection caused by tapeworm larvae lodging in the brain, is one of the leading preventable causes of epilepsy globally. Cerebral malaria, bacterial meningitis, viral encephalitis, and tuberculosis of the brain are other significant contributors. A group of infections known as TORCH infections (toxoplasmosis, rubella, cytomegalovirus, and herpes simplex) can be passed from mother to baby during pregnancy and cause seizures along with developmental delays, vision problems, and other serious complications very early in life.
Bacterial meningitis sometimes causes seizures during the acute illness, but these often don’t persist once the infection is treated. The epilepsy risk comes more from the lasting damage meningitis can leave behind.
Immune System Causes
In autoimmune epilepsy, the body’s immune system mistakenly produces antibodies that attack receptors on brain cells. This triggers inflammation in the brain, which in turn causes seizures. Several specific antibody types have been linked to this process, targeting receptors involved in how nerve cells send and receive signals.
Autoimmune epilepsy can look different from other forms because it often comes on relatively suddenly and may be accompanied by psychiatric symptoms, memory problems, or confusion. Recognizing the autoimmune component matters because the treatment approach is different: rather than only suppressing seizures with medication, doctors may target the underlying immune response.
Prenatal and Early Life Factors
The developing brain is especially vulnerable. Before birth, factors like maternal infections, poor nutrition, and oxygen deprivation can damage fetal brain tissue in ways that lead to epilepsy (or cerebral palsy, or both). Prenatal stress also appears to play a role. Animal studies show that fetuses exposed to significant maternal stress face higher seizure susceptibility, particularly early in life, and evidence in humans suggests that major stress during pregnancy can increase cortisol levels and potentiate febrile seizures in the child.
High fevers in young children can trigger febrile seizures, which are common and usually harmless. Most children who have febrile seizures do not go on to develop epilepsy. However, prolonged or complex febrile seizures, especially in children with other risk factors, can sometimes be an early sign of an epilepsy syndrome.
Metabolic Causes
Metabolic epilepsies result from problems in how the body processes energy or specific nutrients at a cellular level. One well-known example is a condition where the brain can’t properly transport glucose (its primary fuel) across the blood-brain barrier. Without enough energy, brain cells misfire. These metabolic disorders are often genetic in origin but are classified separately because the seizures stem from the metabolic disruption itself rather than directly from the gene mutation.
Metabolic causes are particularly important to identify because some respond to specific dietary interventions. A ketogenic diet, for example, provides the brain with an alternative fuel source and can dramatically reduce seizures in glucose transport deficiency.
When No Cause Is Found
Despite advances in genetic testing and brain imaging, a large share of epilepsy cases have no identifiable cause. Global data from 2021 shows that about 47% of all epilepsy cases fall into the combined category of genetic or unknown origin. For many people, this means extensive testing comes back with no clear answer. This doesn’t change the diagnosis or the treatment approach, but it can be frustrating. As genetic testing becomes more detailed and imaging technology improves, some of these “unknown” cases will likely be reclassified, but for now, living with epilepsy of unknown cause is one of the most common experiences people with the condition share.