Normal body temperature varies from one person to another; it's not uniformly 98.6 F, as physician Carl Wunderlich determined in the 1800s.

Why do you shiver when cold?

Humans are warm-blooded creatures, so our bodies like to maintain internal temperatures separate from and typically above those in their environment. This is made possible by a process known as thermoregulation. When the brain's hypothalamus senses a drop in the body's core temperature, skeletal muscles may be ordered to shiver, sending out waves of muscle contractions and exothermic biochemical reactions whose byproduct includes heat and energy.

Heatstroke occurs when the body reaches 104°F or higher and can't cool itself

Untreated, this medical emergency can result in permanent disability or death. Someone suffering from heatstroke—defined as a core temperature of 104 degrees Fahrenheit but sometimes as high as 106 degrees Fahrenheit—may appear confused and require immediate cooling, ideally with an ice bath.

Most fungal pathogens can't survive the heat of our bodies

Fungal pathogens typically struggle to survive human body temperatures, but researchers hypothesize that global warming conditions will force fungi to adapt to hotter temperatures, with implications for their ability to also survive within our bodies. That type of evolutionary adaptation would lead to more dire health threats for humans.

Heat-related deaths may have climbed by more than 50% over 20 years

Between 2000 and 2009 one study suggests annual heat deaths averaged around 2,670, but between 2010 and 2020 that figure was likely more than 4,000. Researchers studied 54 million death records from the contiguous US and created mathematical models to arrive at these figures, noting that a combination of aging populations and climate change drove that increase.

Feels-like temperature indicates how our skin will feel

When the wind is moving faster, we tend to feel colder due to the so-called "wind chill," which cools our bodies by moving heat away from them and making water evaporate faster. On the other hand, high levels of humidity can make us feel 10 degrees warmer at times.

Understanding why the thermosphere feels cold, despite exceeding 2,000 degrees Celsius

High-energy solar radiation can raise temperatures above 2,000 degrees Celsius (3,632 degrees Fahrenheit), but the air density in this layer is so low that there would be insufficient collisions between energized molecules and a person's skin to cause them to experience this warmth. Variations in the level of solar radiation reaching the layer cause it to swell and shrink.

View thermophiles found in Hot Springs National Park, including nanobacteria and ostracods

Most organisms in this subset of extremophiles live at temperatures between 60 and 80 degrees Celsius (140 to 176 degrees Fahrenheit), which is hot enough to unfold proteins needed for most biochemical reactions. In thermophiles, these molecules, including those needed to replicate DNA during cellular division, are tightly packed and held by stronger bonds to resist changes in shape.

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."

A look at the concentrations of water in the human body and various organs

When we're born, about three-quarters of our bodies are composed of water, dropping to an average of 55-60% for the average adult. The lungs are over 80% water, the kidneys and spleen about 80%, and the heart and brain are approximately three-quarters composed of water—about the same moisture as a banana.

Temperature is a value that controls how predictable or creative an LLM's output is

In large language models, temperature adjusts the randomness in text generation by modifying how often words with lower probabilities are selected next in the sequence. Lower temperatures produce more obvious outputs while higher temperatures produce more creative responses.

Health workers may cool body temperatures with convection cooling

That's spraying a patient with water and putting fans over them. Cooling the body by removing clothing and placing cold water and ice packs—and not blocking evaporation—are essential cooling steps.

Black-body radiation is emitted by everything in predictable ways

All objects above absolute zero emit electromagnetic radiation, with the amount and distribution determined by temperature alone. The shape and intensity of this radiation follow Planck's law, while Wien's law governs the peak wavelength.

Fevers are an immune response to create hurdles for pathogens

Substances called pyrogens prompt the brain to raise the body temperature to levels where bacteria and viruses struggle to survive. The higher temps also support immune cells fighting off the invaders.

Extreme temperature resilience appears to be temporary for tardigrades

Although often considered indestructible, scientists observed these creatures could endure temperatures near 150°C for only a few minutes in their tun state. Outside this state, only half the samples in a Danish study survived 37.1 degrees Celsius (98 degrees Fahrenheit) for 24 hours, making tardigrades extremotolerant rather than extremophiles.

The human brain only uses 5% more energy during active tasks versus resting

Despite only being 2% of the weight of a human body, the average adult brain consumes 20% of its energy, with the majority of it spent on maintaining homeostasis—the stable equilibrium conditions of temperature, acidity, blood sugar, and other properties in the body. For infants, the consumption is closer to 50%.

From the stellar core to the surface, the sun's density decreases from more than 10 times that of lead to 0.00001% that of air.

From the stellar core to the surface, the sun's density decreases from more than 10 times that of lead to 0.00001% that of air, while temperatures drop from millions to thousands.

A temperature of absolute zero is impossible to reach

Zero on the Kelvin scale—equivalent to -273.15 degrees Celsius—describes a system where all atomic motion completely stops, which is forbidden according to thermodynamics. As of 2025, the closest scientists have gotten to absolute zero is 0.00000000004 K.

Without greenhouse gases, Earth's average surface temperature would be below freezing

Atmospheric molecules that absorb and emit infrared radiation from the planet's surface effectively trap additional incident solar energy that would otherwise escape to space. Without the greenhouse effect, the planet's average surface temperature would be approximately -18 degrees Celsius (0 degrees Fahrenheit).

As of 2022, scientists estimate that 117 billion people have been born on Earth

Although no demographic data exist for more than 99% of the time humans have existed, this value can be estimated by tracking approximate population sizes over different periods and the birth rates within those periods. In 2022, about 6.8% of humans that have ever been born were alive.

What summer was like the year you were born

Summers have generally grown warmer, so chances are the first summer of your life was cooler than the most recent one. Stacker used official average weather data for the months of June through August from the year 1920 to 2022 in this fun data dive.

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

This NPR video makes clear that there are surprising similarities between how our bodies and fireworks function. Fireworks and our bodies are both packed with carbon atoms, and have controlled releases of energy that create heat—keeping the human body warm or fueling fireworks' heat, respectively. What's more, the human body even emits a tiny bit of light somewhat similar to fireworks—though it's not visible to the human eye.

Understanding the 1.5 degree Celsius climate benchmark

As more parts of the world are facing extreme weather, from high temperatures to increased natural disasters, there is much debate about what can be done. MIT News explores and explains the 1.5-degree benchmark for limiting the effects of climate change. Read to understand where the planet stands in relation to this threshold and what can be done at the global, regional, and personal levels to “keep 1.5 alive.”

The biology of stress in your body

Stress is a normal human response that has evolved over millions of years to handle changes or threats in our environment. This article is a helpful overview of the biological basics of this response. While it is not harmful to our physiology in the acute setting, chronic stress can lead to damaging changes in the human body over many years.

Why we don't have an answer for the common cold

Since a landmark study of the common cold in 1925, researchers have learned much more about the seasonal ailment. Despite continuous study, people still contract colds for similar periods of time at the same rate with the same symptoms, and there's no vaccine. This article explains how the many viral strains make it hard to control.

Americans only became intolerant of body odor in the last century

Daily bathing only became a societal norm in the last century. Today, Americans routinely bathe and buy more deodorant than any other country, spending roughly $6 billion annually on odor-reducing products. The rise of industrialized soaps, deodorants, and antiperspirants—and extensive marketing around them—stimulated this demand.

How 'vibes' factor into scientists' decisions about using certain units

Although there are absolute quantities from which units can be defined, such as the speed of light and the corresponding light year for distance, the usefulness of units comes from their ability to easily communicate values, rather than how fundamental their origins are. For example, while Kelvin measures absolute temperature, Celsius is scaled to the temperatures of boiling and freezing water, making them more practical for everyday usage.

Visualizing changes in ocean temperatures between 2016 and 2020

How much does the temperature of the sea change in a given year? This visualization helps illustrate the changes by showing sea surface temperature data from January 2016 through March 2020. Sea surface temperature, which refers to water temperature at the sea's surface, plays a significant role in climate and weather.

You can sign up to donate your body to science

It's a separate process to donate your body for medical research; you usually must contact a whole-body donation program directly. Bodies can be donated for medical research, for forensic analysis research, or for medical students to work with as they learn anatomy and surgery, among other purposes. Learn more about numerous accredited organizations that provide human bodies, organs, and tissues to medical researchers and students.

Read a study documenting how 'old people' smell increases with age

Analysis of body odors from individuals aged 26 to 75 confirmed that 2-nonenal, an unsaturated aldehyde with an unpleasant, greasy, and grassy odor, was detected only in subjects aged 40 and older.

All humans share 99.9% of the same DNA

Of the 3 billion base pairs that make up the human genome—the complete set of genetic material for the species—the diversity of humans is the result of variations in about 3 million molecular bases. The closest nonhuman genetic match is the chimp, with 98.8% similar genetics.

Temperature and certain medications can also affect your circadian rhythms

Although light and dark have the largest influence on circadian rhythms, temperature, stress, and certain medications are among the factors that also play a role. Persistent trouble sleeping or staying asleep may signal it’s time to see your doctor to get a better sleep-wake schedule.

The halting of human bone growth helps manage heat produced from metabolism

While fish, amphibians and reptiles get bigger throughout their lives until they die, their slower metabolisms allow their bodies to regulate the resulting smaller temperature increases. In humans, hormones triggered during puberty harden growth plates, ending bone lengthening.

World records are often broken later in the day—and scientists wonder if muscle clocks explain the difference.

Humans have used geothermal resources for thousands of years

In North America, Indigenous peoples viewed hot springs as sacred places and used them for medicinal purposes, cooking, and surviving cold weather. The ancient Greeks and Romans also viewed them as sacred, partaking in hot mineral baths to relieve ailments and using them for space heating.

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).

The value of a dollar differs from state to state

Did you know that $100 is worth 26% less in California than in Arkansas? The value of a dollar isn't consistent in every US state due to a multitude of factors, such as taxes and other varying cost-of-living differences.

Ranking the 10 hottest places on Earth

Death Valley in California often gets the press for the hottest recorded air temperature in the world. What about the runners-up? This list compiles the rest of the Earth's hottest spots, from Jeddah in Saudi Arabia to Kebili in Tunisia.

Earth's core is about 2.5 years younger than its surface according to relativity

Due to differences in where objects are located within gravitational fields, time will run at different rates, which has major impacts on technology that relies on synchronization. For example, GPS satellites run about 38 microseconds faster every day than clocks on Earth's surface, resulting in GPS discrepancies of about six miles, were it not for software corrections.

73% of people report they crave more physical touch in their lives

This figure came from a 2019 survey of 110 adults and examined what's formally called a "touch gap." Touch helps reduce stress, strengthening our immune system, and overall well-being. It can also improve children's health, adjustment, and IQ scores.

Sickle cell trait can put people at elevated risk of heat-related illness

This hereditary blood disorder affects the shape and function of red blood cells. A US military study found that among recruits the incidence rate of exertional heat-related illness was 48% higher among those who had sickle cell trait as compared to those without. Easing into intense exercise and gradually increasing exertional frequency and intensity is recommended.

Keep foods out of the temperature danger zone to help avoid sickness

This graphic can help remind you what temperatures are generally unsafe for perishable food because they can promote and encourage the growth of harmful pathogens.

Lyme disease-causing bacteria predate any suspected biological weapons testing

Borrelia bacteria existed long before any US biological weapons program—or human presence in North America. One study comparing genomes of the bacteria behind Lyme disease collected samples of the bacteria over three decades and calculated that the bacterium has been in North America longer than humans, at least 60,000 years. Other work found related bacteria preserved in amber from millions of years ago.

There's no definitive test for inflammation, or a baseline for what's considered normal

Existing tests can pick up proteins that indicate an immune response—in particular C-reactive protein, which the liver produces when the body's stressed—but that won't tell you why there's inflammation nor if it's chronic or acute inflammation. (Some users may experience a paywall.)

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.

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.

Humans accurately detect their goose bumps only about one-third of the time

Though people do experience goose bumps frequently, goose bump research suggests that humans think they’re experiencing goose bumps in response to emotional cues more often than they truly are.

A list of five scientific theories that were accepted and later disproved

Humoral theory held that everyone's personality derived from different combinations of four bodily fluids: blood, phlegm, yellow bile, and black bile. The phlogiston theory stated that all combustible materials possessed a fire element—phlogiston—that was released and absorbed by the air during burning. When the air became saturated with phlogiston, the fire would go out.

Can we speed up our metabolisms?

Listen to this 31-minute podcast to better understand what science knows and doesn't know about metabolism, as well as the only thing that seems capable of changing it. Scientists understand that the difference between a so-called “fast” and “slow” metabolism does not affect one’s ability to lose weight.

Visualizing obesity rates across the US

Nearly 70% of adults in the US are either overweight or obese, rates that have tripled over the last 60 years. Severe cases have risen tenfold during this period. Factors like location, income level, and demographics contribute to various obesity levels across the US. Visualize the statistics with this article and chart series.

Foodborne illnesses cost our country an estimated $74.7 billion in 2023

A US government estimate puts the cost of all foodborne illness in 2023 at almost $75 billion dollars. In a report published by the US Department of Agriculture’s Economic Research Service, government analysts detailed how the burden of foodborne illness includes medical costs, but also more hidden costs like lost wages. The analysis also breaks down estimated costs by pathogen.