Up to 10% of people worldwide will experience at least one seizure during their lifetime, according to the World Health Organization. Seizures happen when groups of brain cells fire simultaneously and uncontrollably, and a wide range of triggers can set this off, from medical conditions and substance use to sleep deprivation and high fevers. Understanding the full range of causes helps you recognize what might put someone at risk.
What Happens in the Brain During a Seizure
Your brain runs on electrical signals. Billions of nerve cells communicate by firing in coordinated patterns, but a seizure occurs when large clusters of neurons begin firing all at once in a synchronized burst they shouldn’t be producing. Before a seizure starts, small regions of the brain show increasingly unstable activity, with large fluctuations in how fast neurons fire. This local instability generates high-frequency electrical oscillations that spread across areas spanning centimeters of brain tissue.
As this abnormal activity builds, it disrupts the normal movement of charged particles and chemical messengers between cells. Eventually, the chaotic firing becomes persistent enough that all types of brain cells in the affected area begin firing simultaneously, tipping the brain into a full seizure. Depending on where this starts and how far it spreads, the seizure might affect one part of the body or cause a person to lose consciousness entirely.
Structural Brain Abnormalities
Physical changes in the brain’s structure are a major cause of seizures. These abnormalities create areas of tissue that are more electrically excitable than normal, essentially forming a permanent trigger zone. Most structural causes can be identified on an MRI scan.
Traumatic brain injury is one of the most common structural causes. A serious blow to the head can damage brain tissue in ways that make it prone to abnormal electrical activity, sometimes months or even years after the injury. Strokes and other vascular injuries create similar damage by cutting off blood flow and leaving behind scarred tissue. Brain tumors, even slow-growing ones, can irritate surrounding tissue and trigger seizures. Some people are born with structural differences called focal cortical dysplasia, where a small area of the brain didn’t develop properly during fetal growth, creating a seizure-prone zone from birth.
Metabolic and Chemical Imbalances
Your brain is extremely sensitive to the chemical balance of your blood. When key electrolytes or blood sugar levels shift too far from normal, nerve cells become more excitable and can fire uncontrollably.
Low blood sugar (hypoglycemia) has been linked to seizures since the 1940s, and people with no prior seizure history can have one triggered by a severe blood sugar drop. Extremely high blood sugar can also provoke seizures, particularly in a dangerous condition involving severe dehydration and high blood sugar concentrations. Low magnesium levels increase both seizure risk and severity. Animal research demonstrated this clearly: when rats were fed a magnesium-deficient diet, nearly all of them developed seizures, with severity worsening as magnesium continued to drop. Disruptions in calcium balance within brain cells are also a fundamental trigger, particularly after strokes, when the return of blood flow can cause a damaging calcium surge. Low sodium levels can provoke seizures as well, which is why sodium imbalances are monitored carefully in certain medical situations.
Alcohol and Drug Withdrawal
Alcohol withdrawal is one of the most well-known and dangerous seizure triggers. It affects roughly 1% of people going through withdrawal, which is a significant number given how common heavy drinking is. The risk window is specific: seizures typically emerge 6 to 24 hours after someone stops drinking or sharply reduces their intake. Most alcohol withdrawal seizures occur between 12 and 48 hours after blood alcohol levels drop, with 95% falling within a 7 to 38 hour window.
The mechanism is straightforward. Alcohol suppresses brain activity over time, and the brain compensates by becoming more excitable. When alcohol is suddenly removed, the brain is left in an overexcited state with nothing to calm it down, and seizures can result. Withdrawal from certain sedative medications, particularly benzodiazepines used for sleep and anxiety, carries the same risk for the same reason. Stopping these drugs abruptly rather than tapering off gradually can trigger seizures even in people who have never had one.
Medications That Lower the Seizure Threshold
Several classes of commonly prescribed medications can make the brain more susceptible to seizures by lowering what’s called the “seizure threshold,” the point at which abnormal electrical activity tips into a full seizure. This doesn’t mean these medications will cause a seizure in most people, but they increase the risk, especially at higher doses or in people who are already vulnerable.
Certain antibiotics carry this risk, particularly penicillins at high intravenous doses. Some antidepressants can also lower the threshold, though the risk is generally uncommon. When it does happen with older-style antidepressants, seizures typically occur within the first two to six weeks of starting the medication. Newer antidepressants like SSRIs carry a lower but still documented risk.
Fever and Infections
Febrile seizures are the most common type of seizure in young children. They occur when a child’s body temperature rises to about 100.4°F (38°C) or higher during an illness. The seizure isn’t caused by the infection itself but by the rapid rise in temperature. Most febrile seizures are brief, and while terrifying for parents, they typically don’t cause lasting harm or indicate epilepsy.
In adults, infections that directly affect the brain, such as meningitis (infection of the membranes surrounding the brain) and encephalitis (inflammation of the brain itself), can cause seizures by directly irritating and damaging brain tissue. These are medical emergencies that require immediate treatment.
Sleep Deprivation and Lifestyle Triggers
Sleep deprivation is one of the most potent and underappreciated seizure triggers. Most adults need 7 to 8 hours of quality sleep per night, though individual needs vary. Some people function well on 5 hours, while others need 8 to 10 or more. When you consistently get less sleep than your body requires, the brain becomes increasingly excitable. For people with epilepsy, a single night of poor sleep can be enough to trigger a seizure. Even in people without epilepsy, extreme sleep deprivation can push the brain toward seizure activity.
Stress is another significant trigger, likely because it disrupts sleep, alters hormone levels, and changes brain chemistry all at once. Flashing or flickering lights trigger seizures in a subset of people with a condition called photosensitive epilepsy. Hormonal changes also play a role: some women with epilepsy notice that their seizures cluster around specific points in their menstrual cycle, when estrogen and progesterone levels shift.
What to Do if Someone Has a Seizure
If you witness a seizure, the most important thing is to keep the person safe, not to stop the seizure itself. Stay with them and move anything nearby that could cause injury. If they’re on the ground, gently turn them onto their side with their mouth pointing downward so their airway stays clear. Place something soft under their head, remove their glasses, and loosen anything around their neck.
Time the seizure from the start. If it lasts longer than 5 minutes, call 911. You should also call for emergency help if the person has another seizure shortly after the first one, has trouble breathing or waking up afterward, is injured, or has never had a seizure before. If the person has diabetes or is pregnant, call 911 regardless of how long the seizure lasts.
What you should not do matters just as much. Never hold the person down or try to restrain their movements. Don’t put anything in their mouth. Don’t attempt mouth-to-mouth breathing during the seizure. Once it’s over, stay with them as they recover, help them sit up when they’re ready, and calmly explain what happened.