Seizures happen when groups of brain cells fire simultaneously in an uncontrolled burst of electrical activity. Normally, your brain maintains a careful balance between signals that excite neurons and signals that calm them down. When something disrupts that balance, whether temporarily or because of an underlying condition, the result can be a seizure. Around 52 million people worldwide live with epilepsy, but many others experience a single seizure at some point from causes that have nothing to do with epilepsy.
How a Seizure Starts in the Brain
Your brain runs on electrical and chemical signals. Neurons communicate using neurotransmitters, the two most important being glutamate (which excites neurons to fire) and GABA (which tells them to quiet down). A seizure isn’t simply a matter of too many neurons firing. It requires those neurons to fire in sync, creating a wave of abnormal electrical activity that overwhelms the brain’s normal patterns.
Several mechanisms can force neurons into that lockstep pattern. Glutamate-based connections between neurons can create a chain reaction where one cell’s firing triggers the next. Tiny physical bridges between neurons called gap junctions allow electrical current to pass directly from cell to cell, synchronizing them almost instantly. There’s even a paradoxical route through GABA itself: when a single inhibitory neuron quiets a large group of cells at once, the simultaneous “rebound” as they reactivate can launch them all into coordinated firing. Any of these pathways, alone or combined, can tip the brain from normal function into a seizure.
Structural Damage to the Brain
Physical changes in brain tissue are one of the most common causes of recurring seizures. Strokes, traumatic brain injuries, and brain tumors can all create areas of damaged or irritated tissue that become seizure-starting points. A tumor, for instance, causes problems through several routes at once: it physically compresses surrounding tissue, disrupts local blood supply, triggers inflammation, and throws off the chemical environment around nearby neurons. Scar tissue left behind after a stroke or head injury can have similar effects, creating a permanent zone where normal signaling is disrupted.
Genetic Factors
Some people are born with a higher seizure risk because of inherited gene mutations. Most of the mutations identified so far affect ion channels, the tiny pores in neuron membranes that control how electrical signals move in and out of the cell. When these channels don’t open or close properly, neurons become more excitable than they should be.
Dravet syndrome is one well-known example. It typically appears around 6 months of age in previously healthy infants, often starting with prolonged seizures triggered by fever. The condition is most commonly linked to mutations in a sodium channel gene called SCN1A. Other genetic epilepsies involve mutations in genes for GABA receptors, nicotinic acetylcholine receptors, and a growing list of genes that don’t code for ion channels at all. More than 200 different metabolic diseases, many of them genetic, are known to cause seizures through mechanisms like toxic buildup of ammonia, impaired energy production, or vitamin cofactor deficiencies that the brain needs to function.
Metabolic and Chemical Disruptions
Your brain is extraordinarily sensitive to its chemical environment, and relatively small shifts can provoke a seizure even in someone with no history of epilepsy. Low blood sugar is a classic example: glucose is the brain’s primary fuel, and when levels drop too far, neurons lose the energy they need to maintain their normal firing patterns. Low sodium levels in the blood (hyponatremia), often caused by overhydration or certain medications, can have the same effect. High ammonia levels, kidney failure, and severe liver disease all alter the brain’s chemical balance enough to trigger seizures.
These are sometimes called “provoked” seizures because they have a clear, reversible cause. Once the underlying imbalance is corrected, the seizures typically stop and may never return.
Infections That Affect the Brain
Infections that reach the brain or its surrounding membranes are a significant seizure trigger, particularly in children and older adults. Encephalitis (inflammation of the brain itself) and meningitis (inflammation of the protective membranes) can both cause seizures as part of the acute illness.
In the United States, the most common causes of encephalitis include herpes simplex virus (responsible for about 10% of all encephalitis cases), arboviruses like West Nile transmitted by mosquitoes, and enteroviruses. Herpes simplex encephalitis often follows a pattern of headache and fever for up to five days, then progresses to personality changes, seizures, and altered consciousness. Mosquito-borne forms like LaCrosse encephalitis can cause seizures, coma, and permanent brain damage, particularly in children under 16.
Alcohol and Drug-Related Seizures
Alcohol affects the brain’s balance of excitation and inhibition by altering how both glutamate and GABA receptors function. With chronic heavy drinking, the brain adapts to alcohol’s constant presence. When alcohol is suddenly removed, that adapted state becomes dangerously unbalanced. Withdrawal seizures typically occur between 8 and 48 hours after the last drink, making this one of the most predictable seizure triggers.
Certain recreational drugs, including cocaine and synthetic stimulants, can directly provoke seizures by overstimulating the brain. Some prescription medications lower the seizure threshold as a side effect, particularly at high doses or during abrupt withdrawal. Benzodiazepine and barbiturate withdrawal carry a seizure risk similar to alcohol withdrawal, for the same basic reason: the brain has adjusted to a depressant substance and becomes hyperexcitable without it.
Febrile Seizures in Children
Febrile seizures are the most common type of seizure in young children, occurring between the ages of 6 months and 5 years. They’re associated with fevers above 100.4°F (38°C), though there’s no single temperature that triggers them. Each child has their own threshold, and the rate at which the fever rises may matter as much as how high it goes.
These seizures are frightening to witness but are generally not harmful and don’t indicate epilepsy. Most children who have a febrile seizure never have another one, and the vast majority develop normally afterward. The key distinction is that the seizure is caused by the fever itself, not by an infection in the brain.
Sleep Deprivation and Lifestyle Triggers
For people who already have a lower seizure threshold, whether from epilepsy or other factors, certain everyday habits can push them over the edge. Sleep deprivation is one of the most reliable triggers. Missing even a single night of sleep measurably increases brain excitability, which is why sleep-deprived EEGs are sometimes used as a diagnostic tool.
High caffeine intake can lower the seizure threshold by blocking adenosine, a brain chemical that normally helps terminate seizures and promote calm neural activity. Nicotine in high doses has direct convulsive effects in both animal and human studies, while the tissue oxygen deprivation and sleep disruption caused by heavy smoking may indirectly raise seizure risk. Stress, while harder to quantify, is consistently reported by people with epilepsy as their most common seizure trigger.
Photosensitive Seizures
About 3% of people with epilepsy have photosensitive epilepsy, meaning certain visual stimuli can trigger seizures. Flashing lights are the most well-known trigger, but bold, repetitive visual patterns and certain video sequences can have the same effect.
The most dangerous flash frequency peaks around 16 flashes per second (Hz), where nearly 90% of photosensitive individuals show abnormal brain responses. At 3 Hz, only about 3% respond, and above 65 Hz, the response drops to around 4%. This is why broadcast safety guidelines generally prohibit more than 3 flashes per second in television content. The 1997 “Pokémon incident” in Japan, which hospitalized hundreds of children, was traced to a 12 Hz alternation between large red and blue fields, a combination that hit right in the danger zone for both flash rate and color contrast.
For people with photosensitive epilepsy, practical precautions include watching screens in well-lit rooms (which reduces the contrast of flashes), keeping distance from screens, and using display settings that reduce flicker. Many modern video games and streaming platforms now include photosensitivity warnings, though their effectiveness varies.