Seizures in children have many possible causes, ranging from high fevers and infections to genetic conditions and brain injuries. Up to 10% of people worldwide experience at least one seizure during their lifetime, and children are particularly susceptible because their developing brains are more excitable than adult brains. Understanding the cause matters because it shapes both treatment and the likelihood of future episodes.
Febrile Seizures: The Most Common Cause
Fever-related seizures, called febrile seizures, are the single most common cause of seizures in young children. They occur when a child’s temperature rises above 100.4°F (38°C), typically during a viral infection. They’re most common between 6 months and 5 years old, with peak incidence between 12 and 18 months.
The mechanism involves two pathways. First, rising brain temperature directly increases the firing rate of neurons, making them more likely to activate in synchronized bursts. That synchronized overactivity is essentially what a seizure is. Second, the inflammatory chemicals the body releases to fight infection (the same ones that produce the fever) independently lower the brain’s seizure threshold. So it’s not just the heat itself but the immune response behind it.
Most febrile seizures last under five minutes, stop on their own, and don’t cause lasting harm. They’re frightening to witness but are not epilepsy. A child who has one febrile seizure does have an increased chance of having another during a future illness, but the vast majority outgrow them entirely by school age.
Oxygen Deprivation at Birth
In newborns, the leading cause of seizures is oxygen deprivation during or around delivery, a condition called hypoxic-ischemic encephalopathy. When blood flow or oxygen supply to the brain drops, brain cells begin to malfunction and die, and seizures typically appear within the first 24 hours after birth. In more severe cases, seizures can be delayed and initially resistant to treatment, sometimes worsening over the following days as brain injury progresses.
Metabolic problems in the newborn period, including dangerously low blood sugar, can also trigger seizures. Maintaining stable blood glucose is a critical part of newborn care for this reason.
Infections That Affect the Brain
Meningitis and encephalitis, infections of the membranes surrounding the brain or the brain tissue itself, are serious causes of seizures at any age in childhood. The specific germs involved depend on the child’s age. In babies under two months, the usual culprits are group B strep and E. coli. In older infants and children, the bacteria most often responsible are Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae type B.
Viral encephalitis, which involves inflammation of the brain itself, can be caused by herpes simplex virus, Epstein-Barr virus, human herpesvirus 6, influenza, and others. These infections cause seizures both through direct damage to brain tissue and through the intense inflammatory response they provoke. Unlike febrile seizures, seizures from meningitis or encephalitis are a sign of a more dangerous process and require urgent treatment.
Epilepsy and Genetic Causes
When a child has recurring unprovoked seizures (meaning no fever, infection, or injury triggered them), the diagnosis is typically epilepsy. There are many specific epilepsy syndromes in childhood, each defined by the child’s age when seizures start, the type of seizures, and patterns seen on brain wave testing. Some of the more common ones include childhood absence epilepsy, where a child briefly “blanks out” multiple times a day, and childhood epilepsy with centrotemporal spikes (formerly called benign Rolandic epilepsy), which causes focal seizures often during sleep.
On the more severe end of the spectrum is Dravet syndrome, a rare but serious epilepsy that begins in the first year of life. Roughly 90% of children with Dravet syndrome have a mutation in a gene called SCN1A, which provides instructions for building sodium channels in the brain. When those channels don’t work properly, neurons become overactive, leading to frequent and difficult-to-control seizures. In most cases, the mutation is new and wasn’t inherited from either parent, though occasionally a family history of seizures or fever-related episodes suggests it was passed down.
Other genetic epilepsy syndromes include infantile spasms (West syndrome), Lennox-Gastaut syndrome, and juvenile myoclonic epilepsy, among many others. Genetic testing can confirm some of these diagnoses, which helps guide treatment choices.
Head Injuries and Brain Trauma
Traumatic brain injuries from falls, accidents, or abuse can cause seizures in two distinct timeframes. Acute seizures happen within the first week of injury, while the brain is still dealing with swelling, bleeding, or direct tissue damage. Later, some children develop epilepsy months or even years after the injury. In one study, the median time from brain injury to epilepsy diagnosis was two years, and one child developed epilepsy as late as 7.3 years after the original injury.
The strongest risk factors for developing post-injury epilepsy are cortical brain injuries (damage to the outer layer of the brain) and central nervous system infections that complicate the injury. Children with cortical damage had roughly 4.5 times the risk of developing epilepsy compared to those without it. This means that even after a child seems to have recovered from a head injury, seizure risk can persist for years.
Metabolic and Electrolyte Imbalances
The brain is exquisitely sensitive to changes in blood chemistry. Low blood sugar (hypoglycemia) is one of the more common metabolic triggers, especially in newborns and children with diabetes. Low sodium levels can also provoke seizures, particularly when sodium drops below 120 mmol/L. This can happen during severe gastroenteritis with dehydration, water intoxication, or certain hormonal disorders.
These types of seizures are called “acute symptomatic” because they have a clear, reversible cause. Correcting the underlying imbalance usually stops the seizures and prevents recurrence, as long as the trigger doesn’t happen again.
What Happens After a First Seizure
After a child has a first unprovoked seizure, the chance of a second one occurring is between 40% and 50%. That number sounds high, but it also means roughly half of children who have a single seizure never have another. The strongest predictor of recurrence is whether imaging reveals an underlying brain abnormality that caused the seizure. Other factors that increase recurrence risk include an abnormal brain wave test (EEG), abnormalities found on neurological examination, and intellectual disability.
How Doctors Identify the Cause
The diagnostic workup after a seizure depends on the circumstances. An EEG measures the brain’s electrical activity and helps determine what type of seizure occurred and whether it came from one specific area of the brain. This test may be done in the emergency room shortly after a seizure or scheduled as an outpatient visit with a neurologist.
A CT scan is a fast imaging test often done in the emergency room to rule out bleeding or large tumors that need immediate attention. An MRI provides much more detailed pictures and can reveal subtle structural changes in the brain. MRI scans are usually scheduled days or weeks after the initial event, once the acute situation has stabilized. If a genetic cause is suspected, blood-based genetic testing can look for specific mutations like SCN1A and others associated with childhood epilepsy syndromes.
In many cases, especially with febrile seizures in an otherwise healthy toddler, extensive testing isn’t needed. The depth of the workup scales with how unusual the seizure was, the child’s age, and whether there are signs pointing to a more serious underlying condition.