Epileptic seizures happen when nerve cells in the brain fire in sudden, uncontrolled bursts of electrical activity. Anything that disrupts the normal pattern of how these cells communicate, whether it’s a structural injury, a genetic variation, an infection, or a chemical imbalance, can set the stage for seizures. About half of people with epilepsy never find a definitive cause, but for the other half, identifying the underlying problem can shape treatment and outlook.
How Seizures Start in the Brain
Your brain runs on electrical signals. Billions of nerve cells communicate by firing in coordinated patterns, kept in balance by a careful mix of excitatory and inhibitory signals. A seizure occurs when that balance tips: too many cells fire at once, or the signals that normally keep activity in check fail. This can happen in one small region of the brain (producing a focal seizure) or spread across both sides (producing a generalized seizure). The underlying cause determines where and how severely this disruption occurs.
Structural Brain Changes
Physical damage to brain tissue is one of the most straightforward paths to epilepsy. When the brain is injured, scar tissue can form, and that scar becomes a focal point where abnormal electrical activity originates. Several types of structural damage carry significant seizure risk.
Traumatic brain injury is a leading cause, especially when the injury is severe. About 65% of people with penetrating bullet wounds to the brain develop seizures. Among those who need two or more brain surgeries after an injury, over 60% experience seizures. Bleeding between the brain and skull (a subdural hematoma) is another common trigger. If a seizure occurs more than a week after a brain injury, there’s roughly an 80% chance it will happen again, meeting the definition of epilepsy.
Stroke is the single biggest cause of new epilepsy in older adults, accounting for 30% to 50% of cases in people over 65. About 8.8% of ischemic stroke survivors develop seizures. Roughly half of those seizures happen within the first week; the rest emerge weeks, months, or even years later as the damaged brain tissue continues to change.
Brain tumors account for 10% to 30% of new-onset epilepsy in older adults. A tumor doesn’t have to be cancerous to cause seizures. Even a slow-growing, benign mass can press on surrounding tissue and disrupt normal signaling. Developmental abnormalities present from birth, such as areas where the brain’s outer layer didn’t form correctly, fall into this same structural category and are a common finding in children with hard-to-control seizures.
Genetic Factors
In many children with epilepsy, the cause traces back to a genetic variation rather than a visible brain injury. These aren’t always inherited from a parent. Some mutations arise spontaneously during early development.
The most commonly identified genes affect ion channels, the tiny gateways on nerve cells that control the flow of charged particles in and out. When these channels don’t open or close properly, the electrical balance in the brain shifts toward excessive firing. One well-known example involves a gene called SCN1A, which controls sodium channels. Mutations in this gene account for roughly 80% of cases of Dravet syndrome, a severe form of childhood epilepsy that typically begins in the first year of life. Another gene, KCNQ2, affects potassium channels and is linked to seizures that can start within the first days after birth.
Genetic epilepsy doesn’t always mean a single faulty gene. In many cases, multiple small genetic variations combine to lower the brain’s seizure threshold, making a person more susceptible without any one gene being “the cause.” This is why epilepsy can run in families without following a clear inheritance pattern.
Metabolic and Chemical Imbalances
Your brain is extremely sensitive to shifts in blood chemistry. When levels of key minerals or blood sugar swing far enough from normal, seizures can result, even in someone who has never had epilepsy. These are sometimes called acute symptomatic seizures because they stem from a temporary, fixable problem rather than a permanent brain condition.
Sodium is the most common culprit. When blood sodium drops rapidly below about 115 milliequivalents per liter (normal is 135 to 145), generalized convulsive seizures can follow. This can happen with excessive water intake, certain medications, or hormonal imbalances. On the other end, sodium levels rising acutely above 158 to 160 can also provoke neurological symptoms, including seizures.
Low magnesium, low calcium, and abnormal blood sugar levels can all do the same. Severe magnesium deficiency, with levels dropping below about 1 milliequivalent per liter, is particularly known for causing convulsive seizures in both newborns and adults. These metabolic seizures typically stop once the underlying imbalance is corrected, but they can be the first clue to a serious medical problem like kidney failure, liver disease, or an inherited metabolic disorder.
Infections That Affect the Brain
Any infection that reaches the brain can provoke seizures, both during the acute illness and sometimes permanently afterward. Bacterial meningitis, viral encephalitis, malaria, and neurocysticercosis (a parasitic infection caused by tapeworm larvae) are among the most significant causes worldwide. In each case, seizures during the acute phase are associated with higher mortality and a greater chance of developing epilepsy later.
The mechanism is partly direct damage: the infection destroys brain tissue or creates inflammation and swelling. But the inflammatory response itself also plays a role. Chemical signals released by the immune system during a brain infection can increase nerve cell excitability on their own, independent of any tissue destruction. This is why seizures can occur early in an infection, before significant structural damage has had time to develop.
Immune-Related Epilepsy
In autoimmune epilepsy, the body’s immune system mistakenly attacks proteins on the surface of brain cells. This is a relatively recently recognized cause and is worth knowing about because it looks very different from other forms of epilepsy: seizures tend to come on suddenly over days to weeks, often alongside confusion, personality changes, or involuntary movements. A key hallmark is that standard seizure medications don’t work well, but treatments that calm the immune system do.
This type of epilepsy can sometimes be linked to a tumor elsewhere in the body that triggers the immune response, or it can occur on its own. Clues that point toward an immune cause include rapid onset in someone with no prior seizure history, psychiatric symptoms appearing alongside the seizures, and a history of other autoimmune conditions. In some cases, no specific immune marker is found, but the pattern of symptoms and response to immune-targeted treatment confirms the diagnosis.
How Causes Differ by Age
The most likely cause of epilepsy shifts dramatically across the lifespan. In infants and young children, genetic causes dominate. Inherited metabolic disorders and developmental brain abnormalities are also common in this group. Febrile seizures, triggered by high fever, are the most frequent seizure type in early childhood, though most children who have them don’t go on to develop epilepsy.
In teenagers and young adults, head injuries and genetic factors are both significant. By middle age, brain tumors and head trauma become more prominent causes. After age 65, the landscape shifts again: cerebrovascular disease (stroke and related conditions) takes the lead at 30% to 50% of cases, followed by neurodegenerative diseases like Alzheimer’s at 10% to 20%, brain tumors at 10% to 30%, and head trauma at 10% to 20%. Even so, a third to half of epilepsy cases in older adults have no identifiable cause.
Triggers Are Not the Same as Causes
There’s an important distinction between what causes epilepsy and what triggers an individual seizure. A cause is the underlying condition that makes the brain prone to seizures in the first place, like a scar from a past injury or a genetic mutation. A trigger is a temporary factor that provokes a seizure in someone who already has that underlying susceptibility.
Common triggers include sleep deprivation, stress, alcohol use (especially withdrawal), flickering lights, missed medications, illness, and hormonal changes during the menstrual cycle. These factors don’t create epilepsy. They lower the seizure threshold just enough to push an already-vulnerable brain into a seizure. This is why two people with the same underlying cause can have very different day-to-day experiences: one might seize only when sleep-deprived, while another has seizures with no identifiable trigger at all. Recognizing and managing personal triggers is one of the most practical tools for reducing seizure frequency.