Explainer: How heat kills | Science News for Students

Explainer: How heat kills

The human body is good at cooling itself off — but only up to a point
May 2, 2019 — 6:30 am EST
a young man standing outside in the sunshine and sweating in very hot weather

As temperatures skyrocket, the body may not be able to shed excess heat well enough to remain healthy. And not all age groups may suffer equally.

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The human body can’t handle excessive heat. The processes that keep us alive work best within a certain temperature window. That’s generally between about 36° and 37° Celsius (96.8° to 98.6° Fahrenheit), depending on the person.

If someone’s core body temperature goes higher, “the body’s primary response to heat is to try and get rid of it,” explains Jonathan Samet. He’s the dean of the Colorado School of Public Health in Aurora. To get rid of excess heat, blood vessels in the skin dilate, or expand. At the same time, the heart begins beating faster. That pushes blood flow to the skin. There, the blood can release heat to cool down. Meanwhile, sweating kicks in to cool the skin.

When people experience high temperatures again and again, their bodies can get better at shedding excess heat. That’s why someone can move from cold Minnesota to steamy Florida and get used to the higher heat and humidity.

But there is a limit to how much the body can adjust. That limit depends on an individual’s health, as well as the temperature and humidity outside. If the outside temps are hotter than the body, blood at the skin won’t release heat. And where humidity is high, sweating won’t cool the skin. That’s because the sweat can’t evaporate. In 2008, two scientists suggested that humans can’t cool off well if they spend extended time at a wet-bulb temperature over 35° C, or 95° F. (Wet-bulb temperatures are measurements that combine heat, humidity and other factors.)

If the body has to keep dealing with heat without a break, it gets worn out. People can experience heat exhaustion, which causes weakness, dizziness and nausea. If a person still doesn’t cool off, heat stroke may occur. This signals that the body’s ability to regulate heat has broken down. This can allow core body temperature to climb as high as 40° C (104° F). Heat stroke can trigger seizures, convulsions or a coma. Without treatment, death may follow.

No one is immune to heat. But it hits some groups harder than others. The elderly are considered the most vulnerable. One reason: They have fewer sweat glands. But their bodies also respond more slowly to rising temperatures. Children, too, are at risk because they haven’t fully developed the ability to regulate heat. And pregnant women can struggle because of the demands that the fetus puts on the body.

People with chronic diseases such as diabetes, heart disease and obesity also can have trouble cooling their bodies. And people living in poverty often lack air conditioning and other resources to help them beat the heat.

Many people see heat as more of an annoyance than a threat. But climate change, extreme heat and human health are all connected. As Earth’s temperatures climb, extreme heat waves will probably become more common, endangering more people.

Power Words

(more about Power Words)

blood vessel     A tubular structure that carries blood through the tissues and organs.

chronic     A condition, such as an illness (or its symptoms, including pain), that lasts for a long time.

climate     The weather conditions that typically exist in one area, in general, or over a long period.

climate change     Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

coma     A state of deep unconsciousness from which a person cannot be awakened. It usually results from disease or injury.

core     Something — usually round-shaped — in the center of an object.

diabetes     A disease where the body either makes too little of the hormone insulin (known as type 1 disease) or ignores the presence of too much insulin when it is present (known as type 2 diabetes).

dilate     To temporarily swell or expand in size. 

evaporate     To turn from liquid into vapor.

factor     Something that plays a role in a particular condition or event; a contributor.

fetus     (Adj. fetal ) The term for a mammal or other large animal during its later-stages of development in the womb. For humans, this term is usually applied after the eighth week of development.

gland     A cell, a group of cells or an organ that produces and discharges a substance (or “secretion”) for use elsewhere in the body or in a body cavity, or for elimination from the body.

heat exhaustion     An illness that can result from prolonged heat exposure. Symptoms include extreme sweating, fast breathing and a weak pulse. Without treatment, heat exhaustion can turn into heat stroke.

heat stroke     A dangerous illness that can result from prolonged heat exposure. Symptoms tend to include dry skin and a fast heartbeat. Sufferers also may feel dizzy, nauseated and confused. Heat stroke can be fatal.

humidity     A measure of the amount of water vapor in the atmosphere. (Air with a lot of water vapor in it is known as humid.)

immune     (v.) Able to ward off a particular infection. Alternatively, this term can be used to mean an organism shows no impacts from exposure to a particular poison, environmental condition or process.

nausea     A condition that leaves someone feeling to one's stomach, as though one could vomit.

nauseated     The term for feeling as if one might soon vomit.

obesity     (adj. obese) Extreme overweight. Obesity is associated with a wide range of health problems, including type 2 diabetes and high blood pressure.

primary     An adjective meaning major, first or most important.

regulate     (n. regulation) To control with actions.

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

seizure     A sudden surge of electrical activity within the brain. Seizures are often a symptom of epilepsy and may cause dramatic spasming of muscles.