The proteins and sugars on the surface of your blood cells determine your blood type

A brief history of human blood groups

The blood group that determines whether you have type A, B, AB, or O blood was discovered near the turn of the 20th century. This short academic article dives into three main theories about the evolution and emergence of blood groups, the exact nature of which remains unclear.

An interactive explanation of blood transfusion

The antigens and Rh factors of blood cells (which determines your blood type) must be compatible with your immune system—which is why blood transfusions between patients must have matching types. In a mismatch, the immune system will attack and destroy donor blood cells, triggering a potentially fatal reaction.

Seven things you might not know about blood

The red stuff currently pumping throughout your body is a type of connective tissue that is both a solid and a liquid. The liquid portion—plasma—acts as a carrier for the solid portion, which includes blood cells and their biological brethren. Your body is constantly refreshing its supply of blood, creating new cells to replace those that have expired or died. This article overviews some lesser-known facts about blood (and why it's not always red).

Explore the abundance of different types of cells in the human body

Lacking a nucleus and other organelles to maximize space for oxygen-carrying hemoglobin and enhance maneuverability through narrow capillaries, there are about four times as many red blood cells and platelets as all other cell types in the body combined. However, about half of the body's cell biomass consists of skeletal myocytes, or muscle fibers.

The ultrarare 'Er' blood type has been documented only about 40 times

In 2022, the tragic loss of a pregnancy led researchers to the discovery that the rare "Er" blood type could potentially cause a mismatch in blood types between mother and fetus during pregnancy, with devastating consequences. (Some users may encounter a paywall.)

What are 'antibodies'? Read this quick overview

Antibodies are protective proteins produced by your immune system. They attach to antigens (foreign substances) and remove them from your body. Understand this important element of the immune system with this quick overview.

How did segregation in the US affect blood donations?

When the US established its first nationwide network of blood banks in 1941 with the hopes of restoring the dwindling reserves of military members, it was quick to emphasize blood donated by Black Americans wouldn't coat the veins of white servicemen. Historians say this policy was meant to appease white Southerners who believed Black blood was inferior to their own.This policy was leaked to the press that same year.

Allergy tests identify antibodies, but not whether allergy symptoms may appear

Skin prick tests and blood tests, the two most common allergy tests, both detect the presence of allergen-specific antibodies. But just because the body has those antibodies doesn’t mean that a person is “allergic” to a substance or that they will develop symptoms of an allergy when encountering the substance. Allergists work with families to interpret the results and sometimes combine that data with approaches including exposure challenges—giving someone a tiny bit of the food or substance they may be allergic to—under medical supervision.

The inner life of a cell

White blood cells are responsible for protecting the human body from infection. This video uses biophysical data from Harvard researchers to accurately demonstrate what goes on inside one white blood cell as it works within the immune system.

Flu viruses use special proteins to invade and spread in the body

Influenza viruses carry two key surface proteins: hemagglutinin (H), which lets them enter cells, and neuraminidase (N), which helps them escape and spread. These proteins are the basis for the names of flu subtypes like H1N1 and H3N2

DNA's four-letter blueprint makes the variety of all living things possible

The proteins responsible for cellular functions and an organism's traits are built outside of a cell's nucleus from RNA—single-stranded molecules created by reading the information in DNA. DNA's double-stranded structure makes it more stable and allows RNA to be made from either of its complementary strands.

What is the blood brain barrier?

Every blood vessel is lined with endothelial cells that act as filters between blood and the rest of the body. In the brain, these cells are tightly packed together to keep a close watch on what substances can access the vital organ. This protective measure poses an obstacle to drugmakers looking to deliver drugs to the well-defended brain for conditions like Alzheimer's. Watch a quick overview here.

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

Stem cells become specialized cells through the activation or silencing of specific genes

After fertilization, when a sperm cell fuses with an egg, the resulting stem cell is described as totipotent—capable of transforming into any type of body cell or embryonic structures (e.g., placenta). Once differentiated into multipotent cells, they can only specialize further within specific cell type families, such as hematopoietic cells that become platelets and red and white blood cells.

How bitter taste receptors help guard against infection

Receptors for "bitter" tastes evolved to detect potentially harmful plant chemicals, such as nicotine. The receptors also trigger bacteria-fighting responses, including waving hairlike projections to bat away bacteria, ordering the release of bacteria-killing nitric oxide, and calling for antimicrobial protein reinforcements.

Twin studies helped scientists understand why mosquitoes like some of us more than others

A combination of carbon dioxide output, skin chemistry, genetic factors, hormones, and clothing choice can make us particularly vulnerable to mosquito bites. Watch how mosquitoes responded to one man in the video versus his wife, a research approach typically conducted with identical and fraternal twins to test mosquito attractiveness.

Insulin is a hormone that controls blood sugar by helping absorb it into cells

Blood sugar levels increase after a meal when the body starts turning food into usable fuel—sugars, proteins, and more—which are absorbed into the bloodstream through the intestines. Blood sugar levels rise, releasing insulin, and letting sugar in the blood be absorbed into hungry cells, thereby dropping blood sugar levels.

Understanding how atomic structure contributes to each element's properties

The outermost layer of electrons in an atom dictates how it will bond to other atoms. These bonds determine whether elements exist as solids, liquids, or gases in the environment and other characteristics. For example, electrons are freely shared between atoms in metallic bonds, allowing them to immediately re-emit light that strikes them, thus making most metals shiny.

Carrier screening enables individuals without symptoms to see if they carry a gene for disease

Some conditions are autosomal recessive—meaning a person may carry a gene for that condition, but not have symptoms. Cystic fibrosis, sickle cell disease, and Tay-Sachs disease are examples of autosomal recessive diseases in which a person must inherit two copies of a nonfunctioning gene—one from each parent—to develop disease.

Rheumatoid arthritis occurs when the immune system attacks cells within joints

Rheumatoid arthritis is a specific type of arthritis that occurs when the body's immune system attacks normal cells within the connective tissues of the joint and degrades them. This sets off a painful cycle of inflammation and joint destruction that often requires lifelong medication to control.

Melanin and light scattering contribute to different eye colors

Brown eyes have high melanin, while blue eyes have low melanin. Multiple genes contribute to eye color, which can change over time due to melanin buildup. Hazel eyes can shift color depending on ambient light.

Doctors use three key physical markers to determine biological aging

The length of the ends of chromosomes (known as "telomeres"), the gradual change in collections of DNA molecules called "methyl groups", and the secretion of inflammatory proteins are all used as indicators of biological age.

Blood Pressure and Diabetes

New meta-analysis shows blood pressure reductions with ACE inhibitors and ARBs are associated with a lower diabetes risk, but other types of antihypertensive agents have the opposite effect.

Tattoos remain visible on your skin thanks to immune cells called macrophages

Harvard and MIT researchers are developing life-saving tattoos

Tattoos aren’t just a fashion statement. Scientists are trying to find life-saving applications for them. Harvard and MIT researchers are developing tattoo inks that react to body chemicals, alerting diabetics to blood sugar fluctuations or athletes to dehydration. Someday, patients may observe their body chemistry with tattoos that change colors.

How race science influences breast cancer research

Despite researchers' and physicians' pushback, race is still used in studies and clinics to categorize human differences in health conditions and treatment responses. This article explores how race has influenced breast cancer research. Considering race as a factor in cancer research, diagnosis, and treatment can lead to racial inequalities. Sociocultural factors, including food access and air pollution, greatly influence health outcomes.

What's inside an Oreo?

If you look at the ingredient list on your Oreo packaging, you may discover that you don't recognize—or can't even pronounce—some of the listed ingredients, let alone know what they're used for! For instance: Did you know that soy lecithin helps makes oil and water mix? Or that cocoa processed with alkali becomes darker and less acidic? A food scientist breaks down what's inside an Oreo in this seven-minute video.

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.

The syncytiotrophoblast is the outer layer of the placenta and the largest human cell, spanning an area about twice that of a king-sized bedsheet.

Visualize how CRISPR-Cas9—a type of immune system used by single-celled organisms to attack invasive viruses—targets and makes precise changes to a gene's DNA.

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.

All rainbows are 'raincircles' caused by water droplets separating white sunlight into a spectrum of colors, but Earth's surface blocks the bottom half of the circle from our line of sight.

Hookworm infection, though risky, may help fight certain autoimmune conditions by tamping down the immune system's inflammatory response.

The Great Salt Lake's distinct dual coloration results from high-salinity organisms that only live in the northern portion and produce a purple protein.

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.

This poison ivy knowledge quiz—accompanied by photos of the plant's varied forms—may help you identify this common rash-inducing growth.

Studies suggest when you sleep is as important as how much you get, and syncing with your circadian rhythms may lead to less fatigue and improved long-term health outcomes

Crows are believed to have intelligence on par with a seven-year-old child and demonstrate complex behaviors, from problem-solving with tools to recognizing human faces.

Some coin denominations have ridges etched on their sides, partly to prevent counterfeiting, in a practice called 'reeding.'

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

Lesser-known phobias include turophobia, or the fear of cheese, and nomophobia, the fear of being without your cell phone.

Power lines are dotted with large, brightly colored balls to improve the visibility of these thin wires to helicopters and small planes and help prevent potential crashes.

The American cockroach is actually from Africa, an apparent hitchhiker aboard ships carrying enslaved people, with evidence suggesting the bug may have arrived in the New World as early as the 1600s.

Budweiser stores yeast derived from the original 1800s strain in a secret bunker, which only the Head of Yeast Management can access—not even the CEO

The rivalry between Alexander Hamilton and Thomas Jefferson centered on federalism—the question of how much power the federal government should hold relative to the states.

Play the role of a student in a game where you try to navigate college and remain debt-free, selecting different income levels, high school experience, race, ethnicity, and more.

The hormonal disorder PCOS was renamed PMOS in 2026, a move designed to improve care and research by shifting the focus to the hormonal causes of this condition that affects 1 in 8 women.

The Nasdaq's 'Magnificent 7' companies are responsible for roughly 40% of the Nasdaq 100 index's gains, while the remaining 93 companies account for the other 60%.

Mid-century modern graphic designers, known for their bright colors and bold lines in advertising, also found success with children's books.

Prince's sexually explicit 1984 track 'Darling Nikki' attracted the ire of the Parents Music Resource Center, an advocacy group that inspired the Parental Advisory sticker, even though the song ends with a Christian message.