Epileptic seizures are caused by sudden, excessive electrical activity in the brain. At the cellular level, this happens when the balance between signals that excite brain cells and signals that calm them tips too far toward excitation. Around 50 million people worldwide have epilepsy, and in roughly half of all cases, no specific cause is ever identified. For the other half, the causes range from structural brain damage and genetic mutations to infections, metabolic problems, and head injuries.
What Happens Inside the Brain
Your brain cells communicate through chemical messengers called neurotransmitters. Two of the most important are glutamate, which stimulates brain cells to fire, and GABA, which tells them to quiet down. In a healthy brain, these two systems keep each other in check. During a seizure, that balance breaks down: glutamate activity overwhelms GABA’s calming effect, and large groups of neurons begin firing in unison, uncontrollably.
This isn’t just a momentary glitch. Research using both lab and animal models has shown that in epilepsy, the balance between GABA and glutamate is persistently shifted toward excitation. Over time, this imbalance can cause irreversible damage to neurons, which may make future seizures more likely. Think of it like a feedback loop: the more the brain’s electrical system misfires, the easier it becomes for it to misfire again.
Structural Brain Abnormalities
Physical changes in the brain’s structure are one of the most identifiable causes of epilepsy. These abnormalities create areas of tissue that are more prone to generating abnormal electrical signals. Some are present from birth, while others develop after an injury or illness. The most common structural causes include:
- Malformations of cortical development: These are areas where the brain’s outer layer didn’t form correctly during fetal development. Focal cortical dysplasia, a patch of disorganized brain tissue, is one of the most common findings in people with drug-resistant epilepsy.
- Hippocampal sclerosis: Scarring and shrinkage of the hippocampus, a structure deep in the brain involved in memory. This is closely associated with temporal lobe epilepsy, the most common form in adults.
- Brain tumors: Both cancerous and noncancerous growths can irritate surrounding brain tissue and provoke seizures.
- Stroke: When blood flow to part of the brain is cut off, the resulting damage can become a seizure focus. Stroke is the leading cause of new-onset epilepsy in older adults.
- Vascular malformations: Tangles of abnormal blood vessels in the brain that can bleed or disrupt nearby tissue.
Specialized MRI protocols designed specifically for epilepsy can detect many of these abnormalities, including subtle ones that a standard brain scan might miss.
Genetic Causes
Some forms of epilepsy are caused by mutations in genes that control how ions flow in and out of brain cells. These ion channels are the gatekeepers of electrical signaling, so when they malfunction, neurons can fire too easily or too often.
The gene SCN1A is one of the best-understood examples. It provides instructions for building sodium channels, which are essential for neurons to generate electrical impulses. Mutations in SCN1A are found in over 80% of people with Dravet syndrome, a severe form of childhood epilepsy that typically begins with prolonged seizures triggered by fever in the first year of life. The same gene is also involved in a broader condition called genetic epilepsy with febrile seizures plus, along with mutations in several other genes including SCN1B, SCN2A, and GABRG2.
Potassium channel genes matter too. Mutations in KCNC1, which helps regulate high-frequency neuronal firing, cause a loss of the channel’s normal function, leading to a type of progressive epilepsy with myoclonus (sudden, brief muscle jerks). Another potassium channel gene, KCNT1, was linked to epilepsy in 2012 and involves a gain-of-function effect, meaning the channel becomes overactive rather than underactive. Identifying the specific genetic cause matters because it can change which treatments work best, and in some cases, which medications to avoid entirely.
Traumatic Brain Injury
A blow to the head can set the stage for epilepsy months or even years later. The overall 10-year risk of developing epilepsy after any traumatic brain injury is about 4%, but that number varies dramatically depending on the severity and type of injury.
Focal injuries to the brain itself carry the highest risk, with roughly 13% of people developing epilepsy within a decade. Diffuse brain injuries (widespread damage rather than a single point of impact) carry about an 8% risk, while injuries outside the brain tissue, like bleeding between the brain and skull, carry about a 7% risk. Skull fractures alone bring the risk down to around 3%, and mild head injuries sit at about 2.6%. Even that lowest category, though, is meaningfully higher than the general population’s risk, which underscores how sensitive the brain is to physical disruption.
Infections That Affect the Brain
Any infection that reaches the brain or its surrounding membranes can cause seizures, both during the acute illness and long after it resolves. Bacterial meningitis is a well-known example. Seizures can occur during the infection itself due to fever, inflammation, or complications like small strokes within the brain. Some people go on to develop epilepsy permanently.
Globally, certain infections are major drivers of epilepsy in specific regions. Cerebral malaria, caused by the parasite Plasmodium falciparum, is the most important cause of seizures in sub-Saharan Africa. It can produce neurological complications in half of those affected and is particularly dangerous in children. In parts of Latin America, South Asia, and Africa, neurocysticercosis is a leading cause. This happens when a person ingests eggs from a pork tapeworm, and the larvae migrate to the brain and form cysts. As these cysts degenerate and trigger inflammation, seizures often follow, though they can occur at any stage of the infection.
HIV, tuberculosis, and cerebral toxoplasmosis are additional infectious causes, particularly in regions where these conditions are common and treatment access is limited.
Metabolic Disruptions
The brain is exquisitely sensitive to changes in blood chemistry. When certain minerals or blood sugar levels fall too low, neurons become unstable and prone to firing abnormally. Among metabolic causes of seizures, low calcium (hypocalcemia) is the most common, followed by low blood sugar (hypoglycemia) and low sodium (hyponatremia).
Low calcium is frequently tied to vitamin D deficiency, which impairs the body’s ability to absorb calcium from food. Low blood sugar can result from a range of conditions affecting hormone production or energy metabolism. Low sodium, while less common as a seizure trigger, can occur with adrenal gland disorders or when the body retains too much water relative to salt. These metabolic seizures are sometimes called “acute symptomatic” seizures because they’re provoked by a specific, identifiable chemical problem. Correcting the underlying imbalance typically stops the seizures, though in some cases the metabolic stress can cause lasting changes that increase seizure risk going forward.
Triggers vs. Underlying Causes
There’s an important distinction between what causes epilepsy and what triggers an individual seizure in someone who already has it. The causes described above, such as structural damage, genetic mutations, or past infections, create the underlying vulnerability. Triggers are the day-to-day factors that push an already vulnerable brain past its threshold.
The most well-established triggers include sleep deprivation, heavy alcohol use, high stress levels, and flashing or flickering lights (this last one affects a relatively small subset of people with epilepsy). Illicit drug use can also lower the seizure threshold. None of these triggers would typically cause a seizure in someone without an underlying predisposition, but for someone with epilepsy, avoiding known triggers is one of the most practical things they can do to reduce seizure frequency.
Some people have highly consistent, identifiable triggers. Others find that seizures seem to come without warning, with no clear pattern linking them to sleep, stress, or any external factor. This unpredictability is one of the most challenging aspects of living with the condition.