A febrile seizure is a convulsion that can occur when a child has a fever, usually as a result of infection. The seizure often occurs during the first day of a fever, which is defined as a temperature of 101˚F (38˚C) or above. In some cases, a child may not have a fever when the seizure occurs, but develops one a few hours later.

There does not seem to be any link between how severe a fever is and the likelihood of a seizure occurring; the seizures can occur even in the case of mild fever.

The three most common infections to trigger a febrile convulsion are:

• Viral infections such as flu or chickenpox
• An infection of the middle ear
• Tonsillitis

Other infections that may trigger a seizure include:

• Gastroenteritis
• Urinary tract infection
• Respiratory tract infection

Incidence

Febrile seizures are the most common type of fits to occur in infants and young children, with about 1 in 20 children experiencing at least one of these fits at some point. Around 40% of children who have one fit, experience a second one . These fits are most common among children aged between 6 months and 3 years, with the peak risk period being during the second year of life.

Factors that increase a child’s risk of having a recurrence are:

• First seizure at younger than 18 months
• Febrile seizure being the first sign of illness
• A family history of the seizures
• A relatively low body temperature that increases with the first seizure

Symptoms

The main symptom of a febrile seizure is a fit occurring while a child has a fever. Two forms of febrile seizures exist: simple febrile seizure and complex febrile seizure.

Typically, during a simple seizure, the child’s muscles tighten, making the body stiff. The child loses consciousness and the legs and arms shake vigorously. They may also wet or soil themselves, vomit, bite their tongue, foam at the mouth, and their eyes may roll back in their head. The seizure is usually over within a few seconds to 10 minutes and, afterwards, the child may be drowsy for up to an hour.

A complex febrile seizure lasts longer than 15 minutes and symptoms may only affect one part of the body. In some cases, there is seizure recurrence within 24 hours or during the time while the child is unwell.

Although simple febrile seizures can be frightening for those witnessing them, they are usually harmless and do not indicate any long-term health problems. There is no evidence to suggest that brief febrile seizures cause any brain damage, epilepsy, or learning problems.

Prolonged or multiple seizures are associated with an increased risk for epilepsy. However, most children who experience fits do not go on to develop the recurring seizures that are seen in epilepsy and happen in the absence of fever.

For most children, febrile seizures stop by the age of 5 and few children experience more than three of the fits in their lifetime.