what causes a stroke

A stroke happens when blood flow to a part of the brain is cut off or disrupted, depriving brain cells of oxygen and nutrients.¹²

Strokes are divided into two main types based on their underlying cause, along with a temporary condition:¹

1. Ischaemic Stroke (About 85% of cases)

• Cause: A blocked artery cuts off blood flow to a region of the brain.¹²
• How it happens:
  • Thrombosis: A blood clot forms inside a narrowed cerebral artery (often due to atherosclerosis, or cholesterol plaque build-up).
  • Embolism: A blood clot or piece of plaque breaks off from another part of the body (such as the heart or neck arteries) and travels through the bloodstream to block a smaller vessel in the brain.¹²

2. Haemorrhagic Stroke (About 15% of cases)

• Cause: A weakened blood vessel in or around the brain leaks or ruptures.
• How it happens: Blood spills into or surrounding the brain tissue, increasing intracranial pressure and damaging cells. This is frequently driven by chronic high blood pressure, cerebral aneurysms, or vascular malformations.¹²³

3. Transient Ischaemic Attack (TIA)

• Often called a mini-stroke, a TIA is caused by a temporary blockage of blood flow.
• Unlike a full stroke, the blockage breaks up quickly and does not leave permanent brain damage, though it is a critical warning sign of a future stroke.¹²³

Main Risk Factors

Certain medical conditions, lifestyle habits, and unchangeable factors increase the risk of blood vessel damage and stroke:¹

• Medical conditions: High blood pressure (the single biggest risk factor), atrial fibrillation (irregular heartbeat), high cholesterol, diabetes, and sickle cell disease.¹²³
• Lifestyle factors: Smoking, physical inactivity, unhealthy diet, obesity, and heavy alcohol use.¹²
• Unchangeable factors: Advancing age (especially over 55–65), family history of stroke, and ethnic background (such as South Asian, African, or Caribbean descent).¹²

You can read more detailed guidance on prevention and risk management via the NHS or the Stroke Association.¹²If you'd like more tailored information, let me know:

• Are you asking out of general curiosity, or are you trying to understand risk factors for yourself or a loved one?
• Are you looking for information on recognizing early symptoms (like the BE FAST acronym) or recovery support?

A stroke occurs when the blood supply to part of your brain is interrupted or reduced, depriving brain tissue of oxygen and nutrients. Within minutes, brain cells begin to die.

Medical guidance from the NHS Causes of a Stroke Guide categorises strokes into two main types based on their underlying cause:

1. Ischemic Stroke (Blocked Blood Vessel)

• What happens: This is the most common type of stroke, accounting for the majority of cases. It happens when a blood clot blocks or narrows an artery leading to the brain.
• Underlying mechanisms:
  • Thrombosis: A blood clot forms directly inside one of the arteries supplying the brain (often narrowed by fatty build-ups called plaques).
  • Embolism: A blood clot (or other debris, such as a piece of plaque) forms elsewhere in the body—frequently the heart or major neck arteries—and travels through the bloodstream to lodge in a narrower brain artery.

2. Hemorrhagic Stroke (Bleeding in the Brain)

• What happens: This occurs when a blood vessel inside or around the brain bursts, causing bleeding into or around the brain tissue.
• Underlying mechanisms:
  • Intracerebral haemorrhage: An artery inside the brain bursts, commonly driven by chronic high blood pressure weakening the vessel walls.
  • Subarachnoid haemorrhage: Bleeding occurs in the space between the brain and the skull, often caused by a ruptured aneurysm (a weak, balloon-like bulge in a blood vessel).¹

Key Medical Risk Factors

Certain health conditions and lifestyle factors place immense strain on your blood vessels, significantly increasing the risk of a stroke:¹

• High blood pressure (hypertension) — the single most important controllable risk factor.
• Atrial fibrillation (AF) — an irregular and fast heartbeat that can cause blood clots to pool and travel to the brain.
• Type 1 or Type 2 diabetes — damages blood vessels over time.
• High blood cholesterol — contributes to the fatty plaques narrowing the arteries.
• Previous Transient Ischaemic Attack (TIA) — often called a "mini-stroke," which serves as a major warning sign.
• Lifestyle factors — smoking, excessive alcohol consumption, an unhealthy diet, and a lack of physical activity.
• Demographics and medical history — being over 50, having a Black or South Asian background, or having specific conditions like sickle cell disease.¹

Are you asking out of general curiosity, or are you or someone you know currently experiencing symptoms? (Note: If you suspect someone is having a stroke, remember the FAST test—Face, Arms, Speech, Time—and call 999 or your local emergency number immediately).

A stroke happens when the blood supply to part of the brain is interrupted or when a blood vessel in the brain bursts. This stops brain cells from getting the oxygen and nutrients they need, causing them to become damaged or die.

There are three main types of stroke:

1. Ischaemic stroke (most common)

This happens when a blood clot blocks an artery supplying blood to the brain.

Common causes include:

• Blood clots forming in arteries.
• Fatty deposits building up in arteries (atherosclerosis).
• Blood clots travelling from the heart to the brain, sometimes due to an irregular heartbeat (atrial fibrillation).

2. Haemorrhagic stroke

This happens when a blood vessel bursts and bleeds into or around the brain.

Common causes include:

• High blood pressure.
• A weakened blood vessel (aneurysm).
• Abnormal blood vessels.
• Certain blood-thinning medications.

3. TIA (mini-stroke)

A transient ischaemic attack (TIA) happens when blood flow to the brain is temporarily blocked.

Symptoms may disappear within minutes or hours, but it is a serious warning sign that a full stroke could follow.

What increases your risk of having a stroke?

Some of the biggest risk factors are:

• High blood pressure (the biggest risk factor).
• Smoking.
• High cholesterol.
• Diabetes.
• Being overweight.
• Lack of physical activity.
• Excessive alcohol consumption.
• Heart conditions, particularly atrial fibrillation.
• Increasing age.
• Family history of stroke.

How do you recognise a stroke?

Remember FAST:

F – Face

One side of the face droops.

A – Arms

One arm becomes weak or difficult to lift.

S – Speech

Speech becomes slurred, confused or difficult.

T – Time

Call 999 immediately.

(Medical emergency) If you or someone else develops possible stroke symptoms, even if they disappear, call 999 immediately. Don't wait to see if they improve.

Can I ask you something?

Are you asking because:

1. You're worried about your own risk of having a stroke?
2. Someone you know has recently had a stroke?
3. You want to understand what causes strokes in otherwise healthy people?

I can explain the causes in more detail depending on what you're concerned about.