What Causes Febrile Seizures

Febrile seizures are seizures that occur in young children when they have a fever. The exact cause of febrile seizures is not completely understood, but it is believed to be related to the rapid rise in body temperature (a high temperature of 38C (100.4F) or above) that can occur with a fever.

Febrile seizures are thought to be triggered by an abnormality in the brain’s electrical activity, which can be caused by the rapid increase in temperature. The fever itself does not cause the seizure, but rather it triggers the seizure in a child who is susceptible to them.

In most cases, a high temperature is caused by an infection such as:

  • Chickenpox
  • Flu (influenza)
  • Middle ear infections (otitis media)
  • Coronavirus (COVID-19).
  • Encephalitis.
  • Malaria (in regions where this condition is possible).
  • Meningitis.
  • Stomach flu (gastroenteritis).
  • Strep throat.
  • Tonsillitis.
  • Upper respiratory infections.

The fevers that trigger febrile seizures are usually caused by a viral infection, and less commonly by a bacterial infection. The flu (influenza) virus and the virus that causes roseola, which often are accompanied by high fevers, appear to be most frequently associated with febrile seizures.

Risk Factors

  • Young age. Most febrile seizures occur in children between 6 months and 5 years of age, with the greatest risk between 12 and 18 months of age.
  • Family history. Some children inherit a family’s tendency to have seizures with a fever. Additionally, researchers have linked several genes to a susceptibility to febrile seizures.
  • Post-vaccination seizures. The risk of febrile seizures may increase after some childhood vaccinations. These include the diphtheria, tetanus and pertussis vaccine and the measles-mumps-rubella vaccine. A child can develop a low-grade fever after a vaccination. The fever, not the vaccine, causes the seizure.
  • A high fever
  • A previous febrile seizure


The most common complication is the possibility of more febrile seizures (Recurrent febrile seizures). The risk of recurrence is higher if:

  • Your child’s first seizure resulted from a low-grade fever.
  • The febrile seizure was the first sign of illness.
  • An immediate family member has a history of febrile seizures.
  • Your child was younger than 18 months at the time of the first febrile seizure.

It is important to note that febrile seizures are generally not harmful and do not cause any long-term damage to the brain. However, it is still important to seek medical attention if your child has a febrile seizure, as it can be a sign of a more serious underlying condition.