A seizure is a sudden, uncontrolled electrical disturbance in the brain that temporarily alters a person’s consciousness, movement, or behavior. This surge of abnormal electrical activity can manifest in many different ways, from subtle staring spells to full-body convulsive movements. It is important to distinguish this event from epilepsy, which is a chronic neurological disorder marked by recurrent, unprovoked seizures. Seizures can be provoked by a temporary issue or be a symptom of an underlying chronic condition.
Acquired Brain Injuries and Infections
Structural damage to the brain’s tissue often causes seizure activity by creating scarring or abnormal circuitry. Stroke is one of the most frequent causes of seizures in older adults, particularly when the event involves the cerebral cortex. Both ischemic strokes (blocked artery) and hemorrhagic strokes (bleeding into the brain) disrupt normal neuronal communication. This disruption can lead to an acute seizure event or chronic epilepsy later on.
Traumatic brain injury (TBI) is another well-documented cause, with the risk correlating with the severity of the head trauma. Severe TBI can lead to immediate seizures or result in post-traumatic epilepsy years after the initial injury has healed. Brain tumors (neoplasms) also cause seizures by physically compressing or invading brain tissue, disrupting the normal electrical balance of surrounding neurons.
Infections that target the central nervous system can also cause acute symptomatic seizures by triggering inflammation and damaging brain cells. Significant causes include meningitis (inflammation of the protective membranes surrounding the brain and spinal cord) and encephalitis (inflammation of the brain itself). These infections introduce an inflammatory response that lowers the seizure threshold across brain regions.
Internal Chemical Disruptions
Many seizures are caused by systemic issues that temporarily disrupt the brain’s delicate biochemical environment, rather than structural damage. Electrolyte imbalances are a common metabolic cause. Severe hyponatremia (low sodium levels) is a frequently identified trigger because it affects the fluid balance and electrical signaling of neurons. Similarly, severe hypocalcemia (low calcium) and hypomagnesemia (low magnesium) can increase neuronal excitability across the brain.
Glucose disturbances are a major systemic factor, as the brain relies on a stable supply of energy from glucose. Severe hypoglycemia (low blood sugar), often seen in people with diabetes who take too much insulin or skip meals, can cause seizures due to a lack of fuel for brain function. Conversely, extreme hyperglycemia (high blood sugar) can also precipitate seizures, particularly in the context of hyperosmolar states.
Substance use and withdrawal are also common causes, as they acutely alter the balance of neurotransmitters in the brain. Alcohol withdrawal syndrome, for example, is a well-known cause of seizures, typically occurring within 7 to 48 hours after the last drink. Certain prescription medications and illicit drugs, such as cocaine or amphetamines, can intoxicate the central nervous system and directly trigger seizure activity.
Genetic and Developmental Factors
A significant portion of seizure disorders, particularly epilepsy, stem from pre-existing or inherited conditions rather than an acquired injury. Genetic factors are a leading cause of epilepsy, where specific gene changes can alter how brain cells communicate, making them prone to abnormal electrical activity. While some genetic epilepsies are inherited, others are caused by de novo mutations, which are spontaneous changes in a gene that were not present in either parent.
Congenital brain malformations, such as focal cortical dysplasia, are developmental disorders that form before birth and are a frequent cause of drug-resistant epilepsy. In these cases, the brain tissue itself is abnormally formed, creating an inherent source of seizure generation. These structural abnormalities are often subtle and can only be detected through specialized neuroimaging.
Febrile seizures are a distinct, age-dependent phenomenon that is common in young children and is typically provoked by a high fever. Although alarming, these seizures are generally benign and are not considered a sign of chronic epilepsy, usually resolving as the child matures. Despite the identification of many genetic and structural causes, the cause of epilepsy remains unknown in up to 70% of cases, which are then classified as idiopathic.
Distinguishing Rare and Uncommon Triggers
The most common causes of seizures are structural injuries, infections, or acute metabolic imbalances. Therefore, a factor that is not a common cause of a first-time seizure is something that acts as a generalized trigger or is only associated with a very specific, rare form of epilepsy. For instance, psychogenic nonepileptic seizures (PNES) are attacks that resemble epileptic seizures but are caused by psychological stress or trauma, not abnormal electrical brain activity.
Minor sleep deprivation or generalized stress and anxiety are highly common triggers for people already diagnosed with epilepsy. However, they are rarely the sole cause of a person’s first-ever seizure. A new, unprovoked seizure is usually traced back to a more definitive underlying pathology, such as a tumor or stroke, rather than lifestyle factors alone.
Photosensitive epilepsy, where seizures are triggered by flashing lights or contrasting visual patterns, is also not a common cause, affecting only about three percent of people with epilepsy. Genuinely rare causes include certain autoimmune encephalitides or specific parasitic infections like neurocysticercosis, which are highly localized to certain regions of the world.