Hemorrhagic strokes make up roughly 13% of stroke events

Strokes are caused by abrupt stoppage of blood flow to the brain

A stroke occurs when blood flow to part of the brain is suddenly interrupted, either by a blockage (ischemic stroke) or bleeding (hemorrhagic stroke). Each year, nearly 800,000 Americans experience a stroke, with around 85% of them being ischemic.

Visualizing a stroke at the microscopic level

By far the most common type of stroke is what is known as an ischemic stroke. This occurs due to either an embolus (a blood clot that travels to the brain from elsewhere in the body) or a thrombus (a blockage that forms within the brain itself).

Medical recognition of strokes stretches back to ancient Greece

Every minute, 750 milliliters of blood flows to the brain, supplying 20% of the body’s oxygen. A sudden disruption—whether from a clot (ischemic stroke) or a bleed (hemorrhagic stroke)—can be life-threatening. From ancient Greek theories to modern CT and MRI scans, here’s how stroke science has evolved over time.

Someone suffers from a stroke every 40 seconds

Every 40 seconds, someone in the US experiences a stroke—and every minute without treatment destroys millions of brain cells. This explainer breaks down the two main types of strokes, their risk factors, and how early detection could change outcomes in the future.

Left versus right brain strokes vary significantly in long-term effects

Due to the high complexity of the brain, the aftereffects of a stroke can have widely different manifestations, ranging from minor temporary impairments to rapid death. Whether a stroke results in paralysis, speech impairments, loss of bodily function, or death will depend on whether it occurs in the left or right hemispheres or the brain stem.

Why vascular dementia develops

This type of dementia, the second most common form after Alzheimer's, develops due to microscopic bleeds and blood vessel blockages in the brain. The condition isn't curable but medications to help with blood clotting and high blood pressure are part of a suite of interventions designed to minimize damage to the brain.

How tPA, which helps dissolve blood clots, can lessen the severity of a stroke

One of the most exciting recent advances in treating stroke is a medication known as tissue plasminogen activator, or tPA. It is only effective for use in some ischemic strokes, and it must be delivered within 4.5 hours of symptom onset to have a chance at working.

Brain death is very rare—only 2% of hospital patients have brain death in the US

A peer-reviewed analysis examining US hospital billing code data from 2012 to 2016 concluded that the incidence of brain death is about 2% in the country. There was no available information indicating what proportion of those patients underwent organ donation.

Blood clotting is critical to maintaining life, but dysfunctional clots can be fatal

Clotting is how our body stops bleeding in the event of an injury. Typically, platelets adhere to exposed tissue, becoming sticky and forming a plug. Chemical signals trigger the coagulation cascade, converting fibrinogen into fibrin threads that stabilize the plug. This prevents bleeding but can obstruct vessels if overactive or misplaced.

Explore the gap in what Americans die from versus news coverage on death causes

Top killers like heart disease, stroke, and liver disease, though they represent a significant burden nationally, are not often extensively covered in the media.

There have been close to 40 Ebola outbreaks since 1976

Ebola is a rare but deadly virus that causes severe illness, organ damage, and sometimes internal bleeding. It spreads through contact with infected bodily fluids and is most common in parts of sub-Saharan Africa. This explainer covers its symptoms, transmission, and treatment options.

Blood leaves the heart at speeds around 12-16 miles per hour

Blood is pumped around the body through the circulatory system, aka the cardiovascular system. This system comprises the heart, arteries, veins, and capillaries. This video is the first in a multi-part series on the circulatory system, focusing on the role of the heart, the pump that powers the entire system.

Exploring the microscopic composition of blood

Visually, blood looks like a single, red fluid. Zooming in, it is one of the richest substances known, with hemoglobin, plasma, proteins, red and white blood cells, platelets, and more.

Ebola infects and disables immune cells, triggering a cascade of events that leads to small blood clots throughout the body, weakening blood vessels and interrupting blood flow to key organs.

Alzheimer's can lead to brain shrinkage, with an average of around 2% of volume reduction per year

Headache disorders have historically been neglected and under-researched

Confusion between the variety of headaches—from mild discomfort to debilitating pain—and gender bias—migraines primarily affect women—have led to widespread misunderstandings of the medical issue. Medical students in the US may get as little as 30 minutes of instruction on the three major types: migraines, cluster headaches, and tension-type headaches.

Storm surges, not winds, are the leading cause of hurricane-related fatalities

A storm surge is an abnormal rise in water levels generated by a storm that exceeds predicted tides. It is particularly dangerous in coastal regions, where it can generate extreme flooding well before the hurricane makes landfall.

The rarest blood type in the world

Rh-null, also known as “golden blood,” is a blood type so rare, fewer than 50 people are known to have it. It lacks all 61 Rh antigens, making it a universal donor for rare Rh cases, but a nightmare in emergencies, since only Rh-null can be given back.

Rheumatoid arthritis affects about 1% of the population

Rheumatoid arthritis is an autoimmune condition leading to breakdown and inflammation of multiple joints throughout the body. This academic article provides an updated deep dive into our current cellular understanding of rheumatoid arthritis, how it is diagnosed, and the variety of medications available for treating this painful condition.

Swimmer's ear is America's most common waterborne illness

Federal government analysis of the roughly 7 million waterborne illness cases that occur annually in the US found that swimmer's ear comprises some 4.7 million, or 65%, of the annual waterborne illnesses and 20% of hospitalizations. Norovirus infection comes in second place.

Tinnitus estimates vary, but may occur in 10%-15% of the population

This video discusses the mechanisms underlying tinnitus and explores the knowns and unknowns about the condition. Tinnitus most commonly occurs among those with hearing loss, suggesting that cochlear damage may be a factor.

Heatstroke is sometimes missed because the patient is really sweaty

Since the condition involves losing the ability to cool oneself, clinicians sometimes see someone who has exertional heatstroke—like a high school athlete who is really sweaty—and don't realize the heat-related illness has already progressed to heatstroke. Classic heatstroke typically occurs among the very young or the elderly. (Some users may encounter a paywall.)

About 69% of dangerous Black Friday incidents happen inside retail stores

Some posit that this is because tensions tend to run high there as customers fight over a limited physical supply of discounted goods. Another 20% of incidents take place at store entrances, where long lines often form well before the retailer opens its doors.

Bipolar disorder, which is characterized by extreme mood swings, affects nearly 3% of the US population

There are two types of this disorder. Bipolar 1 features a significant manic episode—abnormally elevated mood and frantic energy—followed by repeated depression, while Bipolar 2 vacillates between depressive episodes and hypomania, a milder form of mania, but not a full mania. Listen to this podcast as experts explain the condition.

Prostate cancer is both manageable and the second-deadliest cancer for men

One in 44 men in the US will die from prostate cancer, while one in eight will be diagnosed with it. Commonly viewed as the safest cancer to have, screenings can save lives—but they can also cause complications for otherwise benign cases of the disease.

Horses account for about 96% of the known mammalian cases of West Nile beyond humans

That's partly because horse owners likely notice and take veterinary action when their animals get sick. There is no way to know how frequently wild animals are getting infected with the virus.

Indigenous women are murdered at 10 times the rate of all other ethnicities in the US

Murder is the third-leading cause of death among Indigenous women, who are also 2.5 times more likely to experience violence than any other group. More than 4 in 5 Indigenous women have experienced violence in their lifetime.

Human-to-human transmission of hantavirus remains extremely rare, so the 2026 hantavirus cruise ship outbreak doesn't mean we're facing a COVID-style pandemic risk.

Bone marrow (soft tissue found inside certain bones) generates roughly 500 billion new blood cells each day

See images of medical cases of firework injuries shared on this 'Instagram for doctors.' (Warning: Graphic content)

Hedge funds, the private investment firms that trade a wide swath of financial assets, make money by imposing steep fees on investors and from the fund's investment performance.

Art theft is the third-largest source of criminal revenues worldwide, thanks in part to the subjective nature of valuing a work of art.

View the ten deadliest tornadoes in US history.

Poison ivy's rash-causing compound is found in the plant's roots, stem, and leaves—so coming into contact with any part of the plant can lead to rashes for the 85% of people who are allergic to it.

The deadliest aspect of volcanic eruptions is often not lava, but pyroclastic flows—avalanches of ash, gas, and rock that can move more than half the speed of sound.

US consumers collectively owe more than $1T to credit card companies—almost as much as they owe in auto loans.

Radioactive elements can introduce software errors because the ionizing radiation they produce can detach electrons from atoms, and computer code relies on the distribution of electrons.

The United States is one of only around two dozen countries with a fully federal system of government, in which power is divided between national and state governments.

Larger animals like giraffes, elephants, and blue whales have developed a unique defense against cancer, a phenomenon known as Peto's Paradox

The price of gas is a composite made up of several different factors, with the federal gas tax making up less than 20% of what drivers pay at the pump.

About 12.5% of US adults experience a phobia in their lifetime, a diagnosis that hinges on the intense fear interfering with daily life and persisting for at least six months.

Shooting stars, or meteors, are fragments of asteroids and comets that burn up as they enter Earth's atmosphere, creating streaks in the sky called meteor showers.

The US first hosted the World Cup in 1994, a tournament that lives in soccer infamy for its poor planning and the murder of Colombian player Andres Escobar, who'd accidentally scored on his own net.

Explore an interactive map of battles from the American Revolution, along with detailed summaries of each engagement

Hurricanes, which rely on air consistently spinning in the same direction, cannot cross the equator because air curves in opposite directions north and south of it.

Gerrymandering works through two techniques: cracking opposing voters across districts to dilute their power, and packing them into a few to waste their votes in lopsided majorities.

The Dracula character, now seen as the vampire archetype, was inspired by a seafood-induced nightmare its creator experienced.

Browse a detailed visual analysis of over 200,000 similes—comparisons that often use 'like' or 'as'—from popular fiction to see how frequently writers the same idiomatic expressions.

According to the physics of black holes, our 4D reality may be a hologram—a projection of information coded on a 2D surface on the edge of the universe.

Memecoins are a type of cryptocurrency—a form of digital currency with a wide variety of uses—created around popular 'memes,' or viral internet jokes.