What is a stroke?

A stroke¹ occurs when the blood supply to your brain is interrupted or reduced, preventing brain tissue from getting oxygen and nutrients. Brain cells begin to die in minutes.

A stroke is a medical emergency, and prompt treatment is crucial. Early action can reduce brain damage and other complications.

You can have a stroke and not even know it, particularly in the case of a “mini-stroke,” which is when a stroke’s effects are undetectable (or if the tissue damaged does not serve a critical function).

Stroke is the leading cause² of adult disability worldwide. The good news is that treatments for stroke have become far more effective than in the past.

The three main types of stroke are ischemic strokes, hemorrhagic strokes, and transient ischemic attacks (or “mini-strokes”).

Heatstroke

Heatstroke³ is completely different from a stroke. Heatstroke is a type of heat illness caused by your body overheating from prolonged exposure to or physical exertion in high temperatures. This condition is most common in the summer when temperatures are at their highest.

Heatstroke requires emergency treatment. If left untreated, heatstroke can quickly damage your brain, heart, kidneys, and muscles. The damage worsens the longer treatment is delayed.

Heatstroke probably has the word “stroke” in its name⁴ because high body temperature affects the brain. Like a stroke, heatstroke can destroy brain cells.

Brain stroke

“Brain stroke” is just another term that refers to stroke. The name alludes to the fact that a stroke stops parts of the brain from functioning properly.

Ischemic stroke

An ischemic stroke happens when an artery that supplies blood to the brain becomes blocked.

Hemorrhagic stroke

A hemorrhagic stroke happens when an artery in the brain leaks blood or ruptures (breaks open). The leaked blood puts pressure on brain cells and damages them.

High blood pressure and aneurysms (balloon-like bulges in an artery that can stretch and burst) are examples⁵ of conditions that can cause a hemorrhagic stroke.

Mini-stroke

A “mini-stroke,”⁶ also known as a transient ischemic attack (TIA), is different from an ischemic or hemorrhagic stroke—it occurs when the flow of blood to the brain is blocked for only a short time (usually no more than 5 minutes).

A mini-stroke does not cause lasting damage. When it occurs, the body fights back by producing natural clot-dissolvers (anticoagulants) in the blood. However, a mini-stroke should never be ignored and is a major warning sign of a major stroke ahead.

If you suspect that you’ve had a mini-stroke, get medical help immediately. Call 911 right away. About one-third of people who have a TIA go on to have a more severe stroke within one year.⁷

Stroke causes

There are two main causes of stroke: a blocked artery (ischemic stroke) or leaking or bursting of a blood vessel (hemorrhagic stroke). Some people may have only a temporary disruption of blood flow to the brain, known as a transient ischemic attack (TIA), that doesn't cause lasting symptoms.

Ischemic stroke

This is the most common type of stroke. Approximately 85%⁸ of strokes are ischemic strokes. It happens when the brain's blood vessels become narrowed or blocked, causing severely reduced blood flow (ischemia).

Blocked or narrowed blood vessels are caused by fatty deposits that build up in blood vessels or by blood clots or other debris that travel through your bloodstream and lodge in the blood vessels in your brain.

Hemorrhagic stroke

Hemorrhagic stroke occurs when a blood vessel in your brain leaks or ruptures. Brain hemorrhages can result from many conditions that affect your blood vessels. Factors related to hemorrhagic stroke include:

• Uncontrolled high blood pressure
• Overtreatment with blood thinners (anticoagulants)
• Bulges at weak spots in your blood vessel walls (aneurysms)
• Trauma (such as a car accident)
• Protein deposits in blood vessel walls that lead to weakness in the vessel wall (cerebral amyloid angiopathy)
• Ischemic stroke leading to hemorrhage

A less common cause of bleeding in the brain is the rupture of an abnormal tangle of thin-walled blood vessels (arteriovenous malformation).

Transient ischemic attack (TIA)

A transient ischemic attack (TIA), sometimes known as a “mini-stroke,” is a temporary period of symptoms similar to those you'd have in a stroke. A TIA doesn't cause permanent damage. They're caused by a temporary decrease in blood supply to part of your brain, which may last as little as five minutes.

Like an ischemic stroke, a TIA occurs when a clot or debris reduces or blocks blood flow to part of your nervous system.

Seek emergency care even if you think you've had a TIA. If you've had a TIA, it means you may have a partially blocked or narrowed artery leading to your brain. Having a TIA increases your risk of having a full-blown stroke later.

Stroke risk factors

Many factors can increase your stroke risk. Potentially treatable stroke risk factors include:

Lifestyle risk factors

• Being overweight or obese
• Physical inactivity
• Heavy or binge drinking
• Use of illegal drugs such as cocaine and methamphetamine

Medical risk factors

• High blood pressure
• Cigarette smoking or secondhand smoke exposure
• High cholesterol
• Diabetes
• Obstructive sleep apnea
• Cardiovascular disease, including heart failure, heart defects, heart infection or abnormal heart rhythm, such as atrial fibrillation
• Personal or family history of stroke, heart attack or transient ischemic attack

Other factors associated with a higher risk of stroke include:

• Age: People age 55 or older have a higher risk of stroke than do younger people. Over 70%⁹ of all strokes occur above the age of 65.
• Race: African Americans have a higher risk¹⁰ of stroke than do people of other races.
• Sex:Each year¹¹, about 425,000 women have a stroke—55,000 more than men. This can partly be explained by women's longer average life spans since advancing age is a key element in stroke risk. However, women face unique stroke risks due to hormones, reproductive health, pregnancy, and childbirth.
• Hormones: The use of hormone therapies¹² that include estrogen or progesterone increases the risk of stroke.

Stroke symptoms

Seek immediate medical attention if you notice any signs or symptoms of a stroke, even if they seem to come and go or disappear completely.

Every second counts. Do not wait to see if symptoms stop. The longer a stroke goes untreated, the greater the potential for brain damage and disability.

If you or someone you're with might be having a stroke, pay particular attention to the time the symptoms began. Some treatment options are most effective when given soon after a stroke begins.

Signs and symptoms of stroke include:

• Trouble speaking and understanding what others are saying. You may experience confusion, slur your words or have difficulty understanding speech.
• Paralysis or numbness of the face, arm or leg. You may develop sudden numbness, weakness or paralysis in your face, arm or leg. This often affects just one side of your body. Try to raise both your arms over your head at the same time. If one arm begins to fall, you may be having a stroke. Also, one side of your mouth may droop when you try to smile.
• Problems seeing in one or both eyes. You may suddenly have blurred or blackened vision in one or both eyes, or you may see double.
• Headache. A sudden, severe headache, which may be accompanied by vomiting, dizziness or altered consciousness, may indicate that you're having a stroke.
• Trouble walking. You may stumble or lose your balance. You may also have sudden dizziness or loss of coordination.

“BE-FAST”¹³ is an acronym that can help you remember and recognize the sudden signs of a stroke in yourself or another person:

• Balance: Is the person’s balance off when walking? Does their gait look irregular?
• Eyes: Does the person have trouble seeing in one or both eyes?
• Face: Does one side of the face droop or is it numb? Try asking the person to smile.
• Arm. Is one arm weak or numb? Ask the person to raise both arms. Does one arm drift downward?
• Speech: Is speech slurred, are they unable to speak, or are they hard to understand? Ask the person to repeat a simple sentence. Is the sentence repeated correctly?
• Time: If you observe any of these signs, call 911 or emergency medical help immediately. Every second counts.

Stroke complications

A stroke can sometimes cause temporary or permanent disabilities, depending on how long the brain lacks blood flow and which part was affected. Complications may include:

• Paralysis or loss of muscle movement: You may become paralyzed on one side of your body, or lose control of certain muscles, such as those on one side of your face or one arm.
• Difficulty talking or swallowing: A stroke might affect control of the muscles in your mouth and throat, making it difficult for you to talk clearly, swallow or eat. You also may have difficulty with language, including speaking or understanding speech, reading, or writing.
• Memory loss or thinking difficulties: Many people who have had strokes experience some memory loss. Others may have difficulty thinking, reasoning, making judgments, and understanding concepts.
• Emotional problems: People who have had strokes may have more difficulty controlling their emotions, or they may develop depression.
• Pain: Pain, numbness or other unusual sensations may occur in the parts of the body affected by stroke. For example, if a stroke causes you to lose feeling in your left arm, you may develop an uncomfortable tingling sensation in that arm.
• Changes in behavior and self-care ability: People who have had strokes may become more withdrawn. They may need help with grooming and daily chores.