Multiple sclerosis (MS) is a condition of the central nervous system.
Around 100,000 people in the UK have MS. It's normally diagnosed in people between the ages of 20 and 40, and affects roughly three times as many women as men.
Once diagnosed, MS stays with you for life, but treatments and specialists can help you to manage the condition and its symptoms.
We don't know the cause and we haven't yet found a cure, but research is progressing fast.
What happens in MS?
To understand what happens in MS, it's useful to understand how the central nervous system works.
A substance called myelin protects the nerve fibres in the central nervous system, which helps messages travel quickly and smoothly between the brain and the rest of the body.
In MS, your immune system, which normally helps to fight off infections, mistakes myelin for a foreign body and attacks it. This damages the myelin and strips it off the nerve fibres, either partially or completely, leaving scars known as lesions or plaques.
This damage disrupts messages travelling along nerve fibres – they can slow down, become distorted, or not get through at all.
As well as myelin loss, there can also sometimes be damage to the actual nerve fibres. It is this nerve damage that causes the increase in disability that can occur over time.
As the central nervous system links everything your body does, many different types of symptoms can appear in MS.
The specific symptoms that appear depend upon which part of your central nervous system is affected and the job of the damaged nerve.