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Causes - Stroke

There are 2 main types of stroke:

  • ischaemic strokes
  • haemorrhagic strokes

Ischaemic strokes

Ischaemic strokes are the most common type of stroke. They happen when a blood clot blocks the flow of blood and oxygen to part of the brain.

Blood clots usually form where the arteries have been narrowed or blocked by fatty deposits known as plaques. This process is known as atherosclerosis.

As you get older, the arteries can narrow naturally. But smoking, being overweight and drinking too much alcohol can speed up the process.

Atrial fibrillation can also cause an ischaemic stroke. Atrial fibrillation is a type of irregular heartbeat. This can cause blood clots to form in the heart. These blood clots can travel to the brain and block the flow of blood and oxygen to the brain.

Haemorrhagic strokes

Haemorrhagic strokes are also known as 'cerebral haemorrhages' or 'intracranial haemorrhages'.

These are less common than ischaemic strokes.

They happen when a blood vessel in the skull bursts and bleeds into and around the brain.

The main cause of haemorrhagic stroke is high blood pressure. High blood pressure can weaken the arteries in the brain. This makes them more likely to split or burst.

Things that increase the risk of high blood pressure include:

Haemorrhagic strokes can also be caused by:

  • the rupture of a balloon-like expansion of a blood vessel (brain aneurysm)
  • abnormally formed blood vessels in the brain ('AV malformation')
  • age-related changes to the vessel wall making them leak ('cerebral amyloid angiopathy-CAA')

Reducing the risk of a stroke

Some things that increase your risk of stroke cannot be changed.

These include:

  • age - you’re more likely to have a stroke if you're over 55, but about 1 in 4 strokes happen to younger people
  • family history - if a close relative (parent, grandparent, brother or sister) has had a stroke, your risk is likely to be higher
  • your medical history - if you have already had a stroke, transient ischaemic attack (TIA) or heart attack, your risk of stroke is 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 is higher in these groups

But it’s possible to reduce your risk of having a stroke by making lifestyle changes. These can help to avoid problems such as atherosclerosis and high blood pressure.

Talk to your GP 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

Page last reviewed: 28 June 2023
Next review due: 28 June 2026