Seizures happen when nerve cells in the brain fire electrical signals in an uncontrolled, synchronized burst. The causes range from high fevers in young children to strokes in older adults, and in roughly 50% of epilepsy cases worldwide, no definitive cause is ever identified. Understanding what triggers that abnormal electrical activity helps explain why seizures can look so different from person to person.
How Seizures Start in the Brain
Your brain runs on a careful balance between signals that excite nerve cells and signals that calm them down. The main chemical that ramps up brain activity is glutamate, and the main chemical that dials it back is GABA. A seizure occurs when that balance tips sharply toward excitation: too much glutamate firing, too little GABA restraining it, or both at once.
During a prolonged seizure, the problem can snowball. The receptors that respond to GABA get pulled inside nerve cells, reducing the brain’s ability to apply the brakes. At the same time, receptors that respond to glutamate migrate to the surface of neurons, amplifying excitatory signals. This is one reason seizures that last longer than a few minutes become increasingly difficult to stop and can damage brain tissue through glutamate toxicity.
The Six Recognized Categories of Causes
The International League Against Epilepsy classifies seizure causes into six groups: structural, genetic, infectious, metabolic, immune, and unknown. These categories aren’t mutually exclusive. A person can have a genetic condition that produces a structural brain abnormality, which then causes seizures. Clinicians typically start with brain imaging to look for a structural problem, then work through the other possibilities.
Structural Brain Problems
Physical abnormalities in the brain are among the most identifiable seizure causes. The most common structural findings on brain imaging include hippocampal sclerosis (scarring and shrinkage of a memory-related structure deep in the brain), focal cortical dysplasia (a patch of brain tissue that didn’t develop normally before birth), low-grade brain tumors, and tangles of abnormal blood vessels called vascular malformations. Tuberous sclerosis complex, a condition that causes benign growths in the brain, is another well-established structural cause.
Structural damage can also come from outside events: a traumatic brain injury, a stroke that destroys part of the brain, or an infection that leaves scar tissue behind. Any of these can create a zone of irritable, misfiring neurons that becomes a seizure focus.
Genetic Causes
Some people are born with gene mutations that make their neurons inherently more excitable. One of the most studied epilepsy genes is SCN1A, which provides instructions for building sodium channels in nerve cells. More than 1,800 different mutations have been identified in this single gene. About 80% of SCN1A mutations cause Dravet syndrome, a severe form of epilepsy that begins in infancy and is notoriously difficult to treat.
SCN1A mutations also cause a milder condition called genetic epilepsy with febrile seizures plus, along with several other epilepsy syndromes including West syndrome and Lennox-Gastaut syndrome. Beyond SCN1A, mutations in genes like SCN2A, SCN8A, GABRA1, and GABRG2 can produce similar seizure disorders. In newborns specifically, genetic abnormalities and inborn errors of metabolism are a common cause of epilepsy that begins in the first weeks of life.
Infections That Cause Seizures
Any infection that inflames the brain or its surrounding membranes can provoke seizures. Bacterial meningitis and viral encephalitis are the most familiar examples in high-income countries. Globally, parasitic infections account for an enormous share of seizure-related illness. Neurocysticercosis, caused by the larval stage of a pork tapeworm lodging in brain tissue, is likely the single largest parasitic cause of seizures worldwide. Malaria caused by Plasmodium falciparum can trigger an acute brain swelling that produces seizures, sometimes fatal ones.
Other parasites linked to seizures include toxoplasmosis (particularly dangerous in people with weakened immune systems), schistosomiasis, and echinococcosis. In each case, the parasite either directly invades brain tissue or forms cysts that act like space-occupying masses, irritating surrounding neurons.
Metabolic and Electrolyte Triggers
Seizures caused by metabolic disturbances are considered “acute symptomatic,” meaning they’re provoked by a temporary, correctable problem rather than an underlying brain disease. Low sodium is the electrolyte abnormality most commonly tied to seizures. Sodium levels below 115 milliequivalents per liter that drop rapidly are the classic trigger for generalized convulsions, though even moderately low sodium (126 to 134) can increase seizure duration in people who already have epilepsy.
Dangerously high sodium, typically above 158 to 160, can also cause seizures, and so can low calcium and low magnesium. Low blood sugar is another well-known metabolic trigger. What these conditions share is that they alter the electrical environment around nerve cells, making it easier for neurons to fire in unison. Correcting the underlying imbalance usually stops the seizures without the need for long-term epilepsy medication.
Alcohol and Drug Withdrawal
Alcohol enhances GABA’s calming effect on the brain while suppressing glutamate’s excitatory signals. When a heavy drinker suddenly stops, the brain loses its artificial brake and rebounds into a state of hyperexcitability. Withdrawal seizures typically begin around six hours after the last drink, though they can occur up to 48 hours later. Repeated cycles of heavy drinking followed by withdrawal lower the seizure threshold further each time, a process called kindling, which means each subsequent withdrawal episode carries a higher risk of seizures.
Benzodiazepines work through a similar mechanism, boosting GABA activity. Abrupt discontinuation after prolonged use can produce withdrawal seizures through the same rebound excitability. Cocaine, amphetamines, and certain synthetic drugs can also provoke seizures, though through direct overstimulation rather than withdrawal.
Seizures at Different Ages
Newborns
In the first month of life, the most common seizure causes are acute and provoked: oxygen deprivation during birth (hypoxic-ischemic injury), brain bleeds, infections, and metabolic disturbances. Unprovoked seizures in newborns tend to stem from structural brain malformations or genetic conditions. Identifying whether a newborn’s seizure is provoked or unprovoked shapes the treatment plan and long-term outlook significantly.
Infants and Young Children
Febrile seizures are the most common type of seizure in childhood, affecting 2% to 5% of children in the U.S. and Europe. They occur between the ages of 6 months and 5 years, with a peak around 12 to 18 months, and are slightly more common in boys. These seizures happen during a fever above 100.4°F (38°C) that isn’t caused by a brain infection. There is no single temperature that guarantees a febrile seizure. The highest temperature reached during a fever matters more than how fast the temperature climbs. Most febrile seizures are brief and do not lead to epilepsy.
Older Adults
New-onset seizures in people over 60 have a different profile. Cerebrovascular disease, primarily stroke, accounts for 30% to 50% of cases. A stroke can cause a seizure immediately during the event or weeks to months later, once scar tissue forms. Neurodegenerative conditions like Alzheimer’s disease account for another 10% to 20% of new seizures in this age group. The remainder are spread across tumors, metabolic problems, and medications that lower the seizure threshold.
Immune-Related Seizures
In autoimmune epilepsy, the body’s immune system produces antibodies that attack proteins on the surface of brain cells. This is a relatively recently recognized cause, and it’s important because it responds to immune-suppressing treatments rather than standard seizure medications. Autoimmune encephalitis, particularly the type driven by antibodies against the NMDA receptor, can cause severe, repeated seizures alongside confusion, psychiatric symptoms, and movement problems. It most commonly affects young women but can occur at any age.
When No Cause Is Found
Despite modern imaging and genetic testing, about half of all epilepsy cases globally have no identifiable cause. This doesn’t mean there is no cause. It means current technology can’t detect it. Some of these cases likely involve subtle genetic variations that individually have small effects but collectively tip the balance toward seizure susceptibility. Others may involve microscopic structural changes too small for standard MRI to pick up. As genetic sequencing and advanced imaging continue to improve, the proportion of “unknown” cases is gradually shrinking.