How extreme heat kills, and how to protect yourself

People die from heat when the body can no longer shed it fast enough. That failure can happen even before you feel dangerously overheated, especially when humidity is high, because the heat index measures how hot it really feels once air temperature and relative humidity are combined. In temperatures above 90°F, a fan can actually raise body temperature instead of lowering it, which is why the first line of defense is not moving air alone but getting into air conditioning or a cooling center as quickly as possible.

How heat becomes deadly

The human body has a built-in cooling system, but it has limits. Heat-related illness begins when that system cannot keep body temperature in check, and the danger rises as sweat stops evaporating efficiently in humid air. Once the body cannot cool itself, heat stress can progress from cramps and exhaustion to heat stroke, a medical emergency that can be fatal without rapid treatment.

This is why public health agencies treat extreme heat as more than a discomfort. Heat stress is a leading cause of weather-related deaths, and the National Weather Service says extreme heat has killed more people in the last 10 years than any other weather phenomenon. In the United States, more than 700 people die from extreme heat every year, and in 2023 more than two-thirds of all Americans were under heat alerts, a sign of how widespread the risk has become.

Who faces the greatest danger

Some people are far more likely to get sick or die in hot weather. Older adults, young children, and people with chronic medical conditions are at high risk, especially when they cannot get out of the heat quickly or drink enough fluids. People taking certain medications, including some over-the-counter drugs, may also have impaired heat tolerance because those medicines interfere with the body’s ability to regulate temperature.

Heat does not just trigger one type of illness. It can worsen cardiovascular disease, diabetes, asthma, respiratory illness, mental health conditions, and pregnancy outcomes such as preterm birth and low birth weight. That means a heat wave can affect emergency rooms, clinics, and households far beyond the people already known to be heat-sensitive.

What to do before the next heat wave

The most effective protection starts before temperatures peak. The Centers for Disease Control and Prevention recommends gradual exposure over 7 to 14 days so the body can acclimatize, improving sweating efficiency and circulation stability. That adaptation matters for people who work outdoors, return to summer activity after time away, or suddenly face a hotter climate than they are used to.

A practical heat plan should include: • A place with air conditioning, whether at home, a library, a mall, or a cooling center. • A steady plan for drinking fluids regularly, not just when you feel thirsty. • A way to check on older neighbors, relatives, and people living alone. • Awareness of local air quality, because poor air can make heat exposure harder on the lungs and heart. • A strict rule never to leave a child, disabled person, or pet in a car, even briefly.

Those precautions are simple, but they matter because heat illness can escalate quickly. A person who seems merely tired or flushed can deteriorate into confusion, collapse, or loss of consciousness if they stay hot too long.

How to protect workers on the job

Outdoor workers are obvious casualties of heat, but indoor workers can also face serious occupational heat stress. The risk comes from a combination of environmental heat, metabolic heat from physical labor, clothing, and personal protective equipment, which can trap heat and prevent sweat from evaporating. That means warehouses, kitchens, factories, and construction sites can be just as dangerous as roadsides or fields.

Employers should not treat heat as a personal issue. OSHA and the National Institute for Occupational Safety and Health emphasize prevention programs, along with training for workers and supervisors so they can recognize symptoms and respond with first aid before an emergency develops. That includes planning for breaks, shade or cooling access, water, and a clear process for removing a worker from heat exposure when warning signs appear.

Why acclimatization is not optional

Heat acclimatization is one of the most important tools for reducing preventable illness. The CDC says gradual exposure over 7 to 14 days helps the body adapt by improving sweating efficiency and circulation stability. In practice, that means people need time to build tolerance when they start a summer job, return from vacation, or shift into a hotter climate pattern.

The mistake many people make is assuming one hot day is the same as a season of hot days. It is not. A body that has not acclimatized sweats and circulates blood less efficiently under stress, which can turn routine exertion into a dangerous overload. This is especially important for crews, athletes, and anyone doing outdoor work in heavy clothing or PPE.

The bigger public health picture

Extreme heat is no longer a rare summer event in the United States or Europe. The WHO estimates heat-related deaths in Europe were nearly 63,000 in 2024, and says Europe is warming twice as fast as the rest of the world. The organization also warns that heatwave frequency, intensity, and duration are expected to rise further as climate change, urbanization, and population aging combine to increase risk.

That warning has policy implications as well as medical ones. More urban pavement, more older residents, and more intense heat together mean cities and employers have to plan for cooling access, worker protection, and emergency response before the next dangerous stretch arrives. The burden of heat is already measurable in deaths, alerts, and illness, and the pattern points in one direction: more strain on families, workplaces, and public systems unless preparation becomes routine.

Extreme heat kills when it outpaces the body’s defenses, and it does that fastest when people are isolated, dehydrated, medicated, working hard, or unable to reach a cool space. The next heat wave will reward preparation, not improvisation.