A febrile seizure is a convulsion triggered by fever in a young child, typically between 6 months and 5 years of age. It affects roughly 2 to 5 percent of children in that age range, making it one of the most common neurological events in early childhood. Though terrifying to witness, febrile seizures are generally harmless and don’t cause lasting damage to the brain.
Why Fever Can Trigger a Seizure in Young Children
A child’s brain is still developing through the first several years of life. The protective insulation around nerve fibers (called myelination) is incomplete during this period, which makes the young brain more sensitive to disruptions in normal electrical activity. When a fever pushes body temperature high enough, it can tip that already-sensitive system into a seizure.
Fever causes the body to release inflammatory signaling molecules that increase excitability in the brain’s nerve networks. In a mature brain, these signals are better contained. In a developing brain, the barrier between the bloodstream and the brain is more easily disrupted, letting those signals through more readily. Genetic factors play a role too: some children inherit variations in the channels that control electrical flow in nerve cells, lowering their individual seizure threshold.
One common misconception is that a rapidly spiking fever is the trigger. Research shows the opposite. The peak temperature matters more than how fast the fever rises. A child whose fever climbs gradually to 104°F is at the same risk as one whose temperature shoots up quickly to the same level. The threshold varies from child to child, and some children seize at relatively moderate fevers while others never do.
What a Febrile Seizure Looks Like
The physical signs can be dramatic. A child having a febrile seizure may suddenly lose consciousness, and their body may stiffen or begin shaking and jerking. The shaking can involve the whole body or just the arms and legs. Their eyes may roll back. Some children drool, vomit, or lose bladder or bowel control during the episode. Afterward, the child is typically drowsy, confused, or irritable for a period before returning to normal.
Most febrile seizures last less than a minute or two, though they can feel much longer when you’re watching your child go through one. The vast majority end on their own without any intervention.
Simple vs. Complex Febrile Seizures
Doctors classify febrile seizures into two categories, and the distinction matters for what happens next.
Simple febrile seizures are the most common type. They last less than 15 minutes, involve the whole body (rather than just one side), and happen only once within a 24-hour period. These carry an excellent prognosis and rarely require any follow-up testing.
Complex febrile seizures are less common but warrant closer attention. A febrile seizure is considered complex if it lasts longer than 15 minutes, affects only one part of the body, or occurs more than once within the same day. Complex febrile seizures don’t necessarily mean something is wrong, but they do prompt doctors to look more carefully for underlying causes.
What to Do During a Seizure
If your child has a febrile seizure, staying calm is the single most important thing you can do. The seizure will almost certainly stop on its own. Here’s what to focus on:
- Protect from injury. Ease your child to the ground if they’re standing. Move away furniture, toys, or anything hard or sharp nearby. Place something soft under their head, like a folded towel or jacket.
- Position them safely. Gently turn your child onto their side with their mouth pointing toward the ground. This keeps the airway clear.
- Time the seizure. Check a clock or start a timer on your phone. This information helps doctors later, and it tells you whether the seizure crosses the five-minute mark.
- Loosen clothing around the neck to make sure nothing is restricting breathing.
Equally important is what not to do. Don’t hold your child down or try to stop the shaking. Don’t put anything in their mouth. Don’t attempt mouth-to-mouth breathing during the seizure, and don’t offer food or water until your child is fully awake and alert afterward.
Call 911 if the seizure lasts longer than five minutes, if your child has trouble breathing or doesn’t wake up afterward, if a second seizure follows soon after the first, or if your child is injured during the episode. If this is your child’s first seizure of any kind, it’s worth seeking medical attention even if the seizure stops quickly, so a doctor can confirm it was a febrile seizure and rule out other causes.
What Doctors Check Afterward
After a simple febrile seizure in an otherwise healthy child, extensive testing is usually unnecessary. The American Academy of Pediatrics recommends against routine blood work, brain imaging, or brain wave testing (EEG) for a straightforward simple febrile seizure. These tests don’t change the outcome or management for the vast majority of children.
The main concern doctors want to rule out is whether the fever and seizure might be caused by a brain infection like meningitis. If a child shows signs of meningitis (stiff neck, for example), a spinal tap is warranted. For infants between 6 and 12 months who are behind on their vaccinations, doctors may also consider a spinal tap since younger children with meningitis don’t always show the classic warning signs. But for a fully vaccinated child who looks well after the seizure, observation and treating the underlying fever source is typically all that’s needed.
Chances of It Happening Again
About one in four children who have a febrile seizure will have another one during a future illness. Two factors significantly increase that risk. Children who have already experienced a recurrence are roughly ten times more likely to have another episode. Children who seize at relatively low body temperatures (below about 102.2°F) are also at higher risk, likely because their individual seizure threshold is lower than average.
If your child has risk factors for recurrence, doctors may recommend monitoring them closely for six to eight hours after a febrile seizure to watch for a second episode within the same illness. Peak risk for febrile seizures overall falls between 12 and 18 months of age, and children generally outgrow the susceptibility by age 5 or 6 as the brain matures.
Long-Term Effects on the Brain
This is the question most parents really want answered, and the news is reassuring. Simple febrile seizures do not cause brain damage, intellectual disability, or learning problems. Children who experience them develop normally.
The risk of later developing epilepsy after a simple febrile seizure is approximately 2 percent, only slightly above the roughly 1 percent risk in the general population. Complex febrile seizures carry a somewhat higher risk, but even then, the large majority of children never develop epilepsy. Having a febrile seizure does not mean your child has epilepsy or will develop it. The two conditions share some biological overlap, particularly in how the brain handles electrical activity, but a febrile seizure tied to a fever is a fundamentally different event from an unprovoked epileptic seizure.