Epilepsy has no single cause. It can result from genetic mutations, brain injuries, infections, immune system problems, and metabolic disorders, but in roughly 50% of cases worldwide, no cause is ever identified. Understanding what triggers the condition depends heavily on a person’s age, medical history, and where in the world they live.
How the Brain Produces Seizures
Epilepsy develops when groups of nerve cells in the brain become abnormally excitable and fire electrical signals in uncoordinated bursts. In a healthy brain, nerve cells communicate through tightly regulated electrical impulses. When something disrupts that regulation, whether it’s a scar from a past injury, a genetic difference in how ion channels work, or inflammation from an infection, the result can be seizures. Epilepsy is diagnosed when a person has two or more unprovoked seizures, meaning the seizures aren’t triggered by an obvious immediate cause like a high fever or alcohol withdrawal.
The underlying problem can sit in one specific spot in the brain (focal epilepsy) or involve networks across both hemispheres (generalized epilepsy). Where the disruption lives often determines what kind of seizures a person experiences, from brief staring spells to full-body convulsions.
Genetic Causes
Some forms of epilepsy are caused by mutations in genes that control how nerve cells communicate. These mutations often affect ion channels, the tiny gates that let charged particles flow in and out of brain cells to generate electrical signals. When those gates don’t open or close properly, nerve cells become too excitable.
One well-studied example involves the KCNQ2 gene. Mutations here cause a spectrum of neonatal epilepsy syndromes. On the milder end, babies develop self-limited seizures that typically resolve on their own. On the severe end, these mutations cause developmental and epileptic encephalopathy, a condition where frequent seizures in infancy impair brain development. Children with severe KCNQ2 mutations may be diagnosed with specific syndromes like West syndrome or Lennox-Gastaut syndrome based on their seizure patterns and brain wave recordings.
Other commonly implicated genes include SCN1A, which is linked to Dravet syndrome (a severe childhood epilepsy), and DEPDC5, which plays a role in how brain tissue forms during development. Genetic epilepsy doesn’t always mean the condition was inherited from a parent. Many of these mutations arise spontaneously during early development.
Structural Brain Differences
Any physical abnormality in the brain can serve as a seizure focus. This includes malformations that form before birth, damage from head trauma, brain tumors, and scarring from prior strokes or infections.
Focal cortical dysplasia is one of the most important structural causes. It’s a patch of brain tissue that didn’t develop normally, with disorganized layers of neurons that are prone to generating abnormal electrical activity. It’s the most common structural lesion found in children with drug-resistant focal epilepsy and the second most common in adults with the same condition. When medications fail to control seizures from cortical dysplasia, surgically removing the abnormal tissue is often effective.
Stroke is the dominant structural cause in older adults. It accounts for nearly half of all symptomatic epilepsies in people over 60. Between 30% and 40% of epileptic seizure cases in older adults occur in people with a history of stroke. The damaged brain tissue left behind after a stroke can become a permanent source of abnormal electrical activity, sometimes producing seizures weeks or even months after the initial event.
Infections That Lead to Epilepsy
Infections that reach the brain can cause epilepsy either during the acute illness or years later, after the infection has resolved but left lasting damage. Bacterial meningitis, viral encephalitis (including from herpes simplex virus), and parasitic infections are all established causes.
Globally, the most significant infectious cause is neurocysticercosis, a parasitic infection caused by the pork tapeworm. When tapeworm larvae lodge in the brain, they trigger inflammation and scarring that can produce seizures. The WHO identifies neurocysticercosis as the most frequent preventable cause of epilepsy in the developing world. More than 80% of the 50 million people living with epilepsy worldwide are in lower-income countries, where parasitic and infectious causes play a much larger role than they do in high-income nations.
Immune System Causes
The immune system can sometimes mistakenly attack healthy brain tissue, producing inflammation and seizures. In autoimmune epilepsy, the body generates antibodies that target proteins on the surface of nerve cells. These antibodies interfere with normal signaling between neurons.
The most commonly identified antibodies in autoimmune epilepsy target NMDA receptors, LGI1, CASPR2, and GAD65. NMDA-receptor encephalitis, for instance, often strikes young women and can cause seizures alongside psychiatric symptoms, memory problems, and movement abnormalities. Recognizing immune causes matters because the treatment is fundamentally different: rather than standard seizure medications, these patients need therapies that calm the immune response.
Metabolic Causes
Certain inherited metabolic disorders disrupt the brain’s energy supply or allow toxic byproducts to accumulate, both of which can trigger seizures. One example is GLUT1 deficiency syndrome, where the brain can’t transport enough glucose across the blood-brain barrier. Since glucose is the brain’s primary fuel, the resulting energy shortage causes seizures, often beginning in infancy. A specialized high-fat, low-carbohydrate diet (the ketogenic diet) can bypass the problem by providing the brain with an alternative fuel source.
Other metabolic causes include disorders of amino acid metabolism, problems with how the body processes certain vitamins, and mitochondrial diseases that impair energy production at the cellular level.
Why Causes Vary by Age
The most likely cause of epilepsy shifts dramatically across the lifespan. In newborns and infants, genetic mutations, birth injuries (such as oxygen deprivation), and structural brain malformations are the leading causes. In children and teenagers, genetic epilepsies and infections are more prominent. Young adults are more likely to develop epilepsy from head trauma or autoimmune conditions. And in adults over 60, cerebrovascular disease, particularly stroke, dominates.
This age pattern is one of the first things considered during diagnosis. A 3-month-old with seizures gets a very different workup than a 70-year-old with new-onset epilepsy.
How Causes Are Identified
Finding the underlying cause starts with brain imaging, typically MRI, which can reveal structural abnormalities like cortical dysplasia, tumors, stroke damage, or signs of prior infection. When imaging looks normal and standard evaluations don’t point to a structural, infectious, or metabolic cause, genetic testing becomes an important next step. Modern genetic panels can screen dozens of epilepsy-related genes simultaneously, and whole-exome sequencing can cast an even wider net.
Blood tests can identify metabolic disorders and screen for antibodies associated with autoimmune epilepsy. In some cases, a lumbar puncture helps detect infection or inflammation in the central nervous system. Despite all these tools, roughly half of epilepsy cases worldwide still have no identifiable cause. This doesn’t mean no cause exists. It often means the cause is genetic but involves variants science hasn’t yet linked to epilepsy, or that the structural change is too subtle for current imaging to detect. As diagnostic technology improves, the percentage of “unknown” cases continues to shrink.