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Research reveals the concerning, little-known factor that makes heat waves so deadly — and why it could be getting worse

Higher heat produces more significant heat stress, but other factors also play a role.

More Americans than ever are 'alarmed' or 'concerned' about the overheating of our planet.

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As the world gets hotter, more and more communities are facing heat waves, which can be deadly. However, the risk a heat wave poses doesn't just depend on the temperature. Many other factors, importantly humidity, determine heat stress, Phys.org explained.

What is heat stress?

Heat stress is the impact of high temperatures on the body. Higher heat produces more significant heat stress, but other factors also play a role.

As MIT explained, the human body cools itself down by sweating. The moisture from sweat absorbs heat from the body and evaporates, lowering the body's temperature. 

But when the air is already full of moisture, it's harder for water to evaporate, and people will experience more heat stress. That's why it can feel hotter when the humidity is high.

Other factors that affect heat stress include wind and whether a person is in direct sunlight or shade, Phys.org explained

Some systems try to account for these differences. For example, the National Weather Service uses the WetBulb Globe Temperature to tell the public what the conditions outside will actually feel like.

But even these tools don't fully show the whole picture. Some people are more vulnerable to heat stress than others because of underlying health conditions, and conditions can even vary from neighborhood to neighborhood because of geography and architecture.

Why does heat stress matter?

Hotter temperatures bring a wide range of health risks. As Phys.org pointed out, there is a maximum temperature and humidity that a human body can withstand.

Going past this threshold is deadly even for healthy people, and even lower temperatures can be dangerous for those with underlying health conditions.

Since heat stress increases when humidity increases, communities in more humid areas reach their threshold at a lower temperature than communities in drier areas. 

The areas most in danger of a deadly combination of heat and humidity are India, Pakistan, Southeast Asia, the Arabian peninsula, equatorial Africa, equatorial South America, and Australia, according to Phys.org.

What to do in a heat wave

If you're facing unusually warm weather, cooling off is a safety issue, so here are a few tips to beat the heat. Make sure to drink plenty of water to avoid dehydration due to sweating. 

Limit your activity level as much as possible to keep your body from generating extra heat. Dunk your feet in cold water to cool off rapidly, and use a fan — but only when the temperature is under 95 degrees Fahrenheit.

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