Stroke Causes and Risk Factors

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Strokes are caused by blocked blood flow to the brain (ischemic stroke) or sudden bleeding in the brain (hemorrhagic stroke). Many things raise your risk of stroke, and many of these can be changed to help prevent a stroke or prevent another stroke.

Ischemic stroke

Ischemic strokes are usually caused by a piece of plaque or a blood clot that blocks blood flow to the brain.

When plaque builds up on the inner walls of the arteries, it can lead to a disease called atherosclerosis. Plaque hardens and narrows the arteries, which limits blood flow to tissues and organs. Plaque can build up in any artery in the body, including arteries in the brain and neck. Carotid artery disease is when plaque builds up in the carotid arteries in the neck that supply blood to the brain. It is a common cause of ischemic stroke.

Plaque in an artery can also break open. Blood platelets stick to the site of the plaque injury and clump together to form blood clots. These clots can partly or fully block an artery.

A blood clot that forms in one part of the body can also break loose and travel to the brain. This type of ischemic stroke is called an embolic stroke. Certain heart and blood conditions, such as atrial fibrillation and sickle cell disease, can cause blood clots that lead to stroke.

Inflammation

Chronic (long-term) inflammation contributes to ischemic stroke. Researchers are still trying to understand this fully. We know that inflammation can damage the blood vessels and contribute to atherosclerosis, however. In addition, ischemic stroke can lead to inflammation that further damages brain cells.

Transient ischemic attack

A transient ischemic attack (TIA) is caused by a blockage in the brain just like an ischemic stroke. But the blockage breaks up before there is any damage to your brain. It typically lasts less than an hour but can come and go. Eventually, it can progress to a full stroke. A TIA is also called a mini-stroke.

Hemorrhagic stroke

Sudden bleeding can cause a hemorrhagic stroke. This can happen when an artery in or on top of the brain breaks open. The leaked blood causes the brain to swell, putting pressure on it that can damage brain cells.

Some conditions make blood vessels in the brain more likely to bleed.

• Aneurysm is a balloon-like bulge in an artery that can stretch and burst.
• Arteriovenous malformations (AVMs) are tangles of poorly formed arteries and veins that can break open in the brain.
• High blood pressure puts pressure on the inside walls of the arteries. This pressure makes them more likely to break open, especially when they are weakened because of an aneurysm or AVM.

There are many risk factors for stroke. You can treat or control some of your risk factors, such as high blood pressure and smoking. But you cannot control others such as your age or sudden changes in your health—for example, if you have an aneurysm.

The major risk factors for stroke include:

• High blood pressure
• Diabetes
• Heart and blood vessel diseases: Conditions that can cause blood clots or other blockages include coronary heart disease, atrial fibrillation, heart valve disease, and carotid artery disease.
• High LDL cholesterol levels
• Smoking
• Brain aneurysms or arteriovenous malformations (AVMs): AVMs are tangles of poorly formed arteries and veins that can break open in the brain.
• Viral Infections or conditions that cause inflammation, such as lupus or rheumatoid arthritis: Watch our video to learn more about how SARS-Cov-2, the virus responsible for COVID-19, may raise the risk of stroke. Additionally, we offer information and resources on how we are working hard to support necessary COVID-19 research.
• Age: A stroke can happen at any age, but the risk is higher for babies under the age of 1 and for adults. In adults, the risk increases with age.
• Sex: At younger ages, men are more likely than women to have a stroke. But women tend to live longer, so their lifetime risk of having a stroke is higher. Women who take birth control pills or use hormone replacement therapy are at higher risk. Women are also at higher risk during pregnancy and in the weeks after giving birth. High blood pressure during pregnancy — such as from preeclampsia — raises the risk of stroke later in life.
• Race and ethnicity: In the United States, stroke occurs more often in African American, Alaska Native, American Indian, and Hispanic adults than in white adults.
• Family history and genetics: Your risk of having a stroke is higher if a parent or other family member has had a stroke, particularly at a younger age. Certain genes affect your stroke risk, including those that determine your blood type. People with blood type AB (which is not common) have a higher risk.

Other risk factors for stroke — some of which you can control — include:

• Anxiety, depression, and high stress levels, as well as working long hours and not having much contact with friends, family, or others outside the home 
• Living or working in areas with air pollution
• Other medical conditions, such as certain bleeding disorders, sleep apnea, kidney disease, migraine headaches, and sickle cell disease
• Blood-thinners or other medicines that can lead to bleeding
• Other unhealthy lifestyle habits, including eating unhealthy foods, not getting regular physical activity, drinking alcohol, getting too much sleep (more than 9 hours), and using illegal drugs such as cocaine
• Overweight and obesity or carrying extra weight around your waist and stomach