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Heat exhaustion vs. heat stroke: Knowing the difference is key to preventing illness

Knowing the difference between heat exhaustion and heat stroke is important any time serious heat is in the forecast. (WWMT/Severe Weather Center 3)
Knowing the difference between heat exhaustion and heat stroke is important any time serious heat is in the forecast. (WWMT/Severe Weather Center 3)
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KALAMAZOO, Mich. (WWMT) — Walk out your front door, and the heat and humidity hits like a ton of bricks.

That intense heat and humidity that many of us loathe is more dangerous than one might think. According to the National Oceanic and Atmospheric Administration, heat typically kills more people across the United States each year than any other weather phenomenon.

When triple digit heat indices are expected, it's important to review the symptoms of heat-related illnesses and how to prevent them.

Heat exhaustion

Heat exhaustion is the precursor to heat stroke, which we cover below. According to the Mayo Clinic, the symptoms of heat exhaustion "may include heavy sweating and rapid pulse, a result of your body overheating."

When we're exposed to extreme heat, especially when it is very humid, our body can start to overheat.

Heat exhaustion is characterized by the following symptoms:

  • Heavy sweating
  • Faintness
  • Dizziness
  • Cool, moist skin with goose bumps in the heat
  • Fatigue
  • Weak, rapid pulse
  • Low blood pressure upon standing
  • Muscle cramps
  • Nausea
  • Headache

If you or someone you know thinks you're experiencing heat exhaustion, stop all activity and move to a cooler place to rest.

If conscious, drink water or sports drinks. If symptoms worsen, this might be an indicator of heat stroke setting in.

Heat stroke

Heat stroke is the most serious of any heat-related illness. It's caused by your body's core temperature overheating to 104 degrees or higher, and warrants emergency medical treatment.

Symptoms of heat stroke include:

  • High body temperature
  • Altered mental state or behavior
  • Alteration in sweating
  • Nausea and vomiting
  • Flushed skin
  • Rapid breathing
  • A rapid, strong pulse
  • Headache

In heatstroke due to hot weather alone, skin may become hot and dry to the touch. Health experts also warn, however, that this may not always be the case. If you're exercising or doing strenuous work, your skin may slightly moist. This is known as exertional heat stroke and is most common in athletes and those working in the heat.

Young children and adults over 65 years old are most susceptible to heat exhaustion and heat stroke.

Heat stroke can be deadly and should be treated as an emergency. Call 9-1-1 and seek medical help immediately.


There are many things you can do to prevent heat-related illness, but arguably the four most important include drinking more water than usual, limiting outdoor activities (especially during peak afternoon heating), wearing light-colored and loose-fitting clothing, and avoiding alcohol.

It's also important to know who is most at risk. If you have a condition or take medication that increases your risk of heart complications, then it's a good idea to avoid the heat.

If you're going to be outside, be sure to protect against sunburn. As our skin burns, this inhibits our body's ability to cool itself. Experts at the Mayo Clinic recommend a broad spectrum sunscreen with an SPF of at least 15, reapplied liberally every two hours.

For outdoor workers, the U.S. Occupational Safety and Health Administration recommends drinking four cups of water every hour. Drinking small amounts of water often also was encouraged by OSHA.

It should go without saying, with temperatures in the 80s or 90s, but never leave someone in a parked car. Temperatures inside can become lethal within minutes during extreme heat events.

Why humidity matters

The more humid the air, the less effective your body is able to cool itself off.

Sweat is our body's primary cooling mechanism, but do you ever wonder how that works?

Sweat cools us off due to something called evaporative cooling. As a liquid evaporates, in this case sweat, it uses energy from the air and surface immediately adjacent to it.

As these molecules evaporate from our skin, energy (or heat) stored in our body is released. So when we sweat, our body is cooled through the process.

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When it's humid, this means there's more moisture in the air. This prevents sweat from evaporating as efficiently, and therefore our body isn't able to cool down as quickly.

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