Cells can last in the human body from days to a person's entire life

Cells cannot grow forever due to escalating inefficiency in transporting chemicals

As cells get larger, their volume grows much faster than the surface area through which nutrients and waste products pass, creating a bottleneck that eventually causes cells to die. This forces nearly all organisms visible to the naked eye to comprise enormous numbers of smaller cells, such as the approximately 30 trillion found in the average adult human.

New blood cells are created by hematopoietic stem cells

Blood is made up of several cells with various functions and short lifespans, so the body must have a constant supply of replacements. These replacements are created by hematopoietic stem cells, rare cells that live in bone marrow and can regenerate themselves and blood cells.

Most cells undergo programmed, controlled death

In the average adult human, apoptosis occurs in 50 billion to 70 billion cells daily when proteins managing a cell's life cycle send signals that the cell is damaged, causing it to break apart into smaller pieces that are consumed by white blood cells. The consumption prevents damage from spreading via cell division.

Transplant organs don't always last a lifetime—that's where retransplants come in

How long a transplanted organ lasts depends on a variety of factors including the type of organ and the health of the recipient. Sometimes organs can last many decades, but other times people may need retransplants, which means another transplant following a previous one. Retransplants are most common with kidneys.

Red blood, skin, hair, and nail cells destroy their DNA upon maturing

To maximize the amount of oxygen they carry and more easily alter their shape to fit into narrow blood capillaries, red blood cells destroy their own nuclei. Cornified cells found in hair, nails, and the outermost layer of skin destroy their nuclei and other cellular contents to make room for keratin, which provides durability and structural support.

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.

Each part of the human body experiences aging differently

With global average life expectancy cresting at 73 years, understanding how the body ages is imperative to effective medical treatment and maintaining a desired quality of life. This 13-minute video dives into how the body and its organs age "from head to toe."

What is a cell? A great quick overview.

YourGenome.org furnishes a collection of information on cells and how they work. Every body has trillions of cells, each serving a specific function: making proteins, processing chemicals, and creating energy. Every cell contains a genome, a set of instructions for the cell's function. Brush up on your cells for a better grasp on genetics.

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

Low cell division rates in heart cells make heart cancer particularly rare

The heart's location in the chest also offers protection from external cancer-causing factors. The disease affects about 3 in every 10,000 people, though most cases arise from metastasis from other body parts.

The first line of 'immortal' human cells, which can divide indefinitely and are used in scientific research, was nonconsensually taken from a Black woman.

Embryonic stem cells can develop into any other cell type in the body

Embryonic stem cells emerge around five days after fertilization, during the blastocyst stage of embryonic development. At this point, the embryo consists of about 100 to 150 cells and forms a hollow structure, and these cells are the ultimate source of all other cell types during fetal development.

Studies estimating the number of years between human generations suggest there have been approximately 10,000 to 12,000 generations of humans.

Research has found that the length of human generations has varied throughout the 300,000 years that Homo sapiens have been around, ranging from about 25 to 30 years. These values come from analyzing genetic mutations, since the blend of them passed onto children changes as parents age.

The human body relaxes upon death, including the bowel and bladder, expelling urine and feces

Watch a hospice nurse walk through how death affects the human body and what to expect in the hours and days following the death of a loved one as the body breaks down.

Tardigrades typically live between 3 and 30 months

While avoiding predators, including other tardigrades, nematodes, snails, mites and some fungi, these organisms feed on decaying plant matter and cellular fluid, which they access by puncturing cell walls with their stylets—spear-like structures within their mouths.

One jellyfish species is biologically immortal

Turritopsis dohrnii is a type of jellyfish that can revert back to a juvenile stage after reaching sexual maturity, theoretically allowing it to stay alive for good. But that's a tough sell in a world full of predators. See this list of some of the longest-living species on Earth.

Pig brain cellular activity was restarted hours after death in study published in 2019

Yale University scientists restored basic cellular activity and circulatory function in pig brains about four hours after death with a synthetic cocktail of preservatives and nutrients. This work— which didn't restart electricity activity in the brain or consciousness—could help advance future human stroke and brain injury treatments.

How humans digest food

Every day, the average human eats close to six pounds of food—all of which must be processed by the digestive system. Ten organs collaborate to transform food that the mouth chews into the energy needed to stay alive. (Stretched out, these organs...

How to maintain a healthy gut

Approximately 40 trillion microbes reside in the human gut, forming a unique microbiome, containing hundreds of millions of neurons in what is often called a "mini-brain". A healthy gut is characterized by an effective mucus-lined barrier that prevents unwanted substances from entering the bloodstream. So how do you attain such an ideal gut? This guide outlines a healthy approach to protecting your gut.

The first line of 'immortal' human cells, which can divide indefinitely and are used in scientific research, was nonconsensually taken from a Black woman.

The body's master clock has 20,000 neurons

The suprachiasmatic nucleus, the master clock in mammals, has 20,000 neurons that help maintain the light-dark cycle in the body. Among its jobs: It receives light input information from the retina and then signals peripheral body clocks to act on this information, driving everything from body temperature to hunger.

Women are born with all the eggs they will ever produce in their lifetime

Girls are born with an estimated 1 million to 2 million eggs in their bodies, but around 10,000 die monthly before puberty. Scientists have not yet figured out why there's such an excessive number of eggs prior to menstruation, but they've calculated that there are roughly 300,000 to 400,000 eggs left at puberty.

Some scientists argue NDEs are constructed by the brain, not actually experienced

Despite the powerful memories associated with NDEs, scientists question the idea that the experiences prove consciousness endures after death, opting instead to find physiological explanations for common reports of out-of-body experiences, euphoric and lucid thinking, and more.

Panspermia, the theory that cellular life came from a different planet

One of the most profound mysteries of human life on earth is the presence of living cells: organic, self-organizing, reproducing creatures with a drive to survive within given set conditions. Traditional theories posit life came from divine...

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

As of 2025, most EV batteries retain 95% or more of their range after three years

Data from over 30,000 electric vehicles shows that their batteries are lasting much longer than initially projected, which researchers suggest is due to improved battery management systems and real-world use often being less rigorous than high-performance testing. Cars with 150,000 miles or more that have not had a battery replacement retain at least 83% of their original range.

Accidental ingestion of batteries can be life-threatening

Tissue in the body can serve as a circuit path between the anode and cathode of a battery, resulting in electrical burns and gradual tissue erosion. Stomach acid can corrode a battery and cause its toxic contents to leak, making a person sick. Batteries for internal use, such as in pacemakers, require special designs.

Indefinite cloning of some endangered species may not sustain their longevity because cloning success rates decrease as genetic mutations accumulate.

Tattoos, explained

Tattoos last because immune cells trap ink beneath the skin—but there's more to the story. This overview looks at how ancient cultures used tattoos for status, spirituality and punishment; how technology like the electric tattoo machine transformed the art form, and where innovations like smart tattoos could take it next.

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.

Planarian flatworms are small, aquatic worms with exceptional regenerative capabilities. When cut, the worms can regenerate multiple bodies in a matter of weeks.

Watch what the Ebola virus does inside our cells and organs in order to spread and survive.

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

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

Recent research found that the brain doesn't seem to massively rewire following amputation—upending earlier beliefs about the cause of phantom limb pain.

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.

Learn how your body is, scientifically, like a firework with its own slow, controlled burn.

Apeirophobia is an overwhelming fear of living forever, perhaps stemming from the brain's inability to conceptualize an infinite life.

Volcanoes 'die' when their supply of magma runs out, if they are shifted away from their underlying magma reservoir, or if they get clogged by collapsing or their magma cooling back into rock.

Salvador Dalí believed he was his own dead brother, who had died nine months before he was born

In 1939, baseball star Lou Gehrig delivered his inspirational 'Luckiest Man' speech after retiring due to the health condition that now bears his name.

Coral reefs get their colors from zooxanthellae—microorganisms that line corals' digestive tracts and provide them with sugars in exchange for a home within this protective tissue.

Discover the catastrophic consequences of a failure of the US electrical grid—something that is more likely than many Americans think.

Track the location of the Voyager probes, currently between 13 and 15 billion miles away from Earth.

While atoms are normally made of protons, neutrons, and electrons, exotic ones have been built with antimatter—alternate versions of normal matter that live for fractions of a second and are about a billion times as rare.

This site reaches millions of visitors who are tired of AI chatbots and seeking human connection. Pretend to be an AI chatbot and ask questions, provide answers, and draw for people in real time.

The US Constitution is widely regarded as the longest-standing written national constitution still in force—see how it has influenced rights worldwide.

As of 2025, the most cited papers in science include a review of graphene, methods to improve image recognition, streamlining electron density calculations, and optimizing protein studies.

In 1963, a basement renovation in Turkey revealed a passageway to a hidden, multilevel underground city that once housed as many as 20,000 people

US housing costs have risen by roughly 175% between 1991 and 2026—but a growing number of Gen Zers are becoming homeowners anyway. In 2025, 4% of homebuyers were Gen Z, up from 3% the year before.