Febrile seizure: seizure in ≤60-month-old child accompanied by a fever (≥100.4°F or 38°C by any method) but without central nervous system infection or prior unprovoked seizure (American Academy of Pediatrics [AAP] guidelines use 6 months as the lower age limit, whereas International League Against Epilepsy uses 1 month.)

  • Two types:
    • Simple: febrile seizures that are generalized from the start, last <15 minutes, AND do not recur in 24 hours
    • Complex
      • Febrile seizures that are focal (including postictal weakness), last ≥15 minutes, OR occur >1 time in 24 hours (simple febrile seizures plus—a proposed new category for those whose only complex feature is >1 seizure in 24 hours)
      • Febrile status epilepticus: one febrile seizure or series of febrile seizures without full recovery in between lasting ≥30 minutes


  • Age
    • Most febrile seizures occur between 6 months and 3 years of age.
    • Peak age is about 18 months.
  • Type
    • 65–70% are simple febrile seizures.
    • 20–35% are complex febrile seizures.
    • ~5% are febrile status epilepticus.
  • Timing of seizure
    • ~20% before or <1 hour of fever onset
    • ~60% 1 to 24 hours after fever onset
    • ~20% >24 hours after fever onset


  • Most common childhood seizure
  • Febrile seizures occur in 2–5% of children in the United States and Western Europe, 9–10% of children in Japan, and 14% of children in Guam.


  • Positive family history of febrile seizures
  • Prior febrile seizure (see “Prognosis” section)


Usually multifactorial or polygenic inheritance


  • Antipyretics do not reduce the recurrence risk of simple febrile seizures.
  • Very low risk of febrile seizure after some vaccinations, for example, DPT, influenza and MMR(V)
    • Nonetheless, routine childhood immunizations are recommended, as the morbidity of vaccine-preventable illnesses outweighs the risk of febrile seizures.
    • Centers for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices (ACIP) does not list febrile seizures as a contraindication to any commonly used vaccine; seizures ≤3 days after a previous dose of DTP/DTaP is listed as a precaution for future doses.


  • Elevated temperatures in developing brain may increase neuronal excitability.
  • Fever increases cytokines that may enhance neuronal excitability.
  • Genetic factors
  • Hyperventilation from fever causes a respiratory alkalosis that may promote seizures.


  • Any viral or bacterial infection
    • Human herpesvirus 6 and 7
    • Influenza A
    • Shigellosis
  • Vaccines
    • Influenza, DPT, and MMR(V)
    • These may increase the risk of febrile seizures but not epilepsy.


  • Generalized epilepsy with febrile seizures plus (GEFS+)
    • Febrile seizures beyond 6 years of age or afebrile seizures of varying types ranging from mild to severe
    • Multiple genes identified including SCN1A, SCN2A, SCN1B, GABRG2, GABRD, and PCDH19
  • Febrile infection–related epilepsy syndrome (FIRES)
    • Catastrophic epileptic encephalopathy of unknown etiology that begins with a febrile illness and refractory status epilepticus
    • High morbidity and mortality

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