There are two main types of stroke – ischaemic strokes and haemorrhagic strokes. They affect the brain in different ways and can have different causes.
Ischaemic strokes are the most common type of stroke. They occur when a blood clot blocks the flow of blood and oxygen to the brain.
These blood clots typically form in areas where the arteries have been narrowed or blocked over time by fatty deposits known as plaques. This process is known as atherosclerosis.
As you get older, the arteries can naturally narrow, but certain things can dangerously accelerate the process.
Another possible cause of ischaemic stroke is a type of irregular heartbeat called atrial fibrillation. This can cause blood clots in the heart that break up and escape from the heart, and become lodged in the blood vessels supplying the brain.
Haemorrhagic strokes – also known as cerebral haemorrhages or intracranial haemorrhages – are less common than ischaemic strokes. They occur when a blood vessel within the skull bursts and bleeds into and around the brain.
The main cause of haemorrhagic stroke is high blood pressure, which can weaken the arteries in the brain and make them prone to split or rupture.
Things that increase the risk of high blood pressure include:
- being overweight or obese
- drinking excessive amounts of alcohol
- a lack of exercise
- stress, which may cause a temporary rise in blood pressure
Haemorrhagic strokes can also occur as the result of the rupture of a balloon-like expansion of a blood vessel (brain aneurysm) or abnormally formed blood vessels in the brain.
Reducing the risk of a stroke
It's not possible to completely prevent strokes because some things that increase your risk of the condition can't be changed, including:
- age – you're more likely to have a stroke if you're over 65 years old, although about a quarter of strokes happen in younger people
- family history – if a close relative (parent, grandparent, brother or sister) has had a stroke, your risk is likely to be higher
- ethnicity – if you're south Asian, African or Caribbean, your risk of stroke is higher, partly because rates of diabetes and high blood pressure are higher in these groups
- your medical history – if you've previously had a stroke, transient ischaemic attack (TIA) or heart attack, your risk of stroke is higher
However, it's possible to significantly reduce your risk of having a stroke by making lifestyle changes to avoid problems such as atherosclerosis and high blood pressure.
You should also seek medical advice if you think you may have an irregular heartbeat. This can be a sign of atrial fibrillation, which increases the risk of a stroke.
Read about preventing strokes.