What causes epilepsy?

Different epilepsies are due to many different underlying causes. The causes can be complex, and sometimes hard to identify. A person might start having seizures because they have one or more of the following.

• A genetic tendency, passed down from one or both parents (inherited).
• A genetic tendency that is not inherited, but is a new change in the person's genes.
• A structural (sometimes called 'symptomatic') change in the brain, such as the brain not developing properly, or damage caused by a brain injury, infections like meningitis, a stroke or a tumour. A brain scan, such as Magnetic Resonance Imaging (MRI), may show this.
• Structural changes due to genetic conditions such as tuberous sclerosis, or neurofibromatosis, which can cause growths affecting the brain.

Tuberous sclerosis  – a rare condition that causes growths in organs including the brain. 

Neurofibromatosis  – a genetic condition that can cause growths on the nerves. 

Some researchers now believe that the chance of developing epilepsy is probably always genetic to some extent, in that any person who starts having seizures has always had some level of genetic likelihood to do so. This level can range from high to low and anywhere in between.

Even if seizures start after a brain injury or other structural change, this may be due to both the structural change and the person's genetic tendency to seizures, combined. This makes sense if we consider that many people might have a similar brain injury, but not all of them develop epilepsy afterwards.

Seizure thresholds

Part of the genetic likelihood of developing seizures is called a seizure threshold. This is our individual level of resistance to seizures. Any of us could have a seizure under certain circumstances, but for most people, their natural resistance to having seizures is high enough to stop that happening.

Our seizure threshold is one part of our genetic make-up which can be passed from parent to child. So the chance of you having seizures may depend partly on whether either or both of your parents has epilepsy.

If you have a low seizure threshold, your brain is less resistant to seizures. So you are more likely to suddenly start having seizures for no obvious reason than someone with a high seizure threshold.

Your doctors may be able to tell you what has caused your seizures to start, but this is not always possible. Research continues into understanding more about why seizures happen in some people and not in others.

Epilepsy Society is grateful to Dr F J Rugg-Gunn, Consultant Neurologist & Honorary Associate Professor, Clinical Lead, Chalfont Centre for Epilepsy, who reviewed this information.

Information updated: May 2024