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Climate change is driving temperatures up all over the planet. In some places, temperatures are already exceeding the limits of human survivability which is believed to be 95 degrees with 100% humidity, 115 degrees with 50% humidity, and 135 degrees in dry heat. Beyond those temperatures, the body cannot cool itself and organs begin to fail.

The danger from heat-related trauma is real and increasing every day. In an average year, more than seven hundred people die from extreme heat in the United States alone. That number is expected to climb into the thousands within the next decade.

How the human body cools itself in heat

Our body can survive a decrease in core temperature of 10, even 20 degrees, but our body can only survive an increase in core temperature of five to seven degrees. When the body detects an overheating situation, a part of the brain (the hypothalamus) sends signals to organs and systems in the body that quickly begin to react to cool down.

photo of man touching his head

First, the body signals the sweat glands to release sweat. When the sweat evaporates, it carries heat with it and thus helps lower body temperature. This is the reason higher humidity decreases the temperature at which we can survive. In high humidity, sweat will not evaporate as efficiently.

Secondly, the body can cool itself through a process called vasodilation. Blood vessels under the skin begin to expand and the heart begins to pump harder. This increases blood flow to the skin and has the effect of transferring heat through the blood to the body’s surface – away from the warm inner body. The heat is then released through the skin as heat radiation (in scientific terms, via convection).

Just as an air conditioner transfers heat from inside the home and releases it outdoors through a vent, the body transfers heat from inside and releases it outside the body through the above methods. It’s important to understand that cooling the body off involves transferring heat away from the body. When the body cannot cool itself effectively, we must implement our own means to transfer that heat away.

When to worry about the heat

The maximum temperature a human can survive is dictated primarily by the level of humidity (although sunlight and the wind also play a factor). When humidity is high, sweat cannot evaporate which keeps your body from releasing heat as fast as it needs to. Scientists call this combination of heat and humidity the “web-bulb temperature” – the lowest temperature at which an object can cool down via evaporating moisture. Currently it is believed the maximum temperatures a human can survive are 95 degrees with 100% humidity, 115 degrees with 50% humidity, and 135 degrees with zero humidity.

Certain factors can also increase your risk of overheating. Children under the age of 4 and adults 65 and older are at increased risk for heat-related illnesses because their body’s ability to regulate temperature is more difficult at these ages.

Some medications can also increase your risk of overheating. For instance, medications used to treat high blood pressure or heart conditions may reduce your ability to stay hydrated which can cause heat exhaustion and heat stroke. Some drugs for epilepsy and Parkinson’s, have been found to reduce sweating and make it harder to stay cool.

Obesity causes your body to retain more heat. It also makes it more difficult to cool the body down if you are overweight. And obesity stresses the body in other ways which takes away energy the body needs to fight the heat.

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Moving to a warmer location or hotter climate introduces a risk of overheating and requires acclimation to the new environment. When you rapidly move from a colder to a warmer climate, like going on vacation in a hotter location, your body may not be able to adjust to the warmer weather. You may have more difficulty regulating your body temperature as a result.

The difference between heat exhaustion and heat stroke and the signs to look for

The body overheats through two stages and each stage demonstrates unique symptoms. The first stage, heat exhaustion, occurs when the body loses excess amounts of water and salt, typically from sweating. The second stage, heat stroke, is a serious medical emergency that occurs when your body is unable to control its internal temperature and begins to shut down.

Signs of heat exhaustion

Signs of heat exhaustion include the following:

  • weakness
  • heavy sweating
  • fast pulse
  • cramps
  • nausea or vomiting
  • lightheadedness, dizziness, feeling faint
  • pale, cold, clammy skin

Signs of heat stroke

If the body cannot cool itself, it will transcend heat exhaustion to the life-threatening stage called heat stroke. The signs of heat stroke include:

  • elevated body temperature (greater than 104 degrees)
  • rapid and strong pulse
  • throbbing headache
  • loss or change of consciousness
  • confusion, staggering
  • shortness of breath
  • seizures
  • not sweating
  • hot, red, dry, or moist skin

A heat stroke can be deadly and even if survived, can cause permanent damage to your heart, kidneys, liver, lungs, and brain.

How to keep your body cool in extreme heat

The first step to battling elevated temperatures is to stay hydrated. The body’s ability to sweat will be limited if you are dehydrated. You’ll need to drink more water than usual and not wait until you are thirsty. This means keeping a schedule and sticking to it. For instance, take a few sips of water every 15 minutes or snack on foods with high water content such as strawberries, cucumbers, lettuce, and watermelon.

man in black crew neck t shirt drinking yellow liquid from plastic bottle

This also means of course; you must ensure you have plenty of supplies on hand. Fluids such as milk, which contains salt and sugar, or coconut water, which contains vital elements lost through perspiration, may be even better than water for rehydration. Similarly, switchel or haymaker’s punch is a traditional electrolyte drink used by farmers for centuries. You can make it with the following ingredients:

  • 1 cup maple syrup, honey, or brown sugar
  • 1 cup apple cider vinegar
  • ½ cup light molasses
  • 1 tablespoon ground sugar
  • 1-quart cold water

And of course, alcoholic beverages and caffeine which act as diuretics, promote dehydration and should be avoided.

Use common sense and take advantage of your environment. Limit the use of heat generating electronics such as stoves and ovens and turn off computers, appliances, and incandescent light bulbs. Stay in air-conditioned buildings as much as you can. If one is not available, use a public facility or sit inside an air-conditioned car. If an AC is not available, use fans to circulate air throughout the home.

When the outside temperature falls below the inside temperature (evenings and night), open windows and turn on fans. Point them outward to pump heat out and draw cool air in through other open windows and doors. When the sun rises and it begins to heat up again, close doors and windows and cover them with curtains, blankets, and blinds to keep cool indoor air inside as long as possible.

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Note that the effectiveness of fans diminishes as the temperature grows. For instance, fans are ineffective in temperatures above 95 degrees (since they simply blow warm air over the body which contributes to dehydration). Also, don’t forget that fan motors themselves generate additional heat.

Limit outdoor activity or at least, delay it until evening, night, or morning. Carefully consider tasks that must be completed and pace your activities. Begin work in the late evening or night and continue until morning, allowing time to sleep during the day (preferably midday) if possible.

During midday, find shade, stay still, and keep cool. Shade created via higher objects allows air to circulate underneath (i.e. trees with low branches removed) and is better than shade created by low hanging objects (e.g. a tent). Cool air will settle in low lying areas such as valleys and around creeks making these areas excellent locations to cool off.

Wear lightweight, loose, light-colored clothing that allows air to circulate around the skin. If you find the clothing too hot, don’t remove it but instead, drench it with water. The water in the shirt will evaporate and cool the skin off.

Evaporating water can carry cool air with it. Jars of water placed in a natural airflow or wet sheets draped over a window can produce a cooling effect. If ice is available, you can place it in a shallow pan in front of a fan so that the fan blows air over the ice. As the ice melts, you can reuse the water to stay cool.

Shower with cool water or place your feet in a bucket of water. Wet towels and bandannas and place them on the shoulders and neck. You can also use a spray bottle to occasionally spritz water on your skin. Understand that cold water constricts blood vessels and thus, a cold shower reduces blood flow to the skin which causes the body to retain even more heat. A warm or cool shower is better.

Contrary to widely held belief, applying water (or ice) to your head does not help keep the body cool. The best areas to place cooling objects are the groin, armpit, neck, or inner wrist where large veins that run near the skin can be cooled.

Water and ice are not the only objects that can help you cool off. Animals lay on the ground in high heat and use the cool earth to draw heat away. Even a grassy area can be used to siphon heat off the body. Put as much of your body as possible in contact with the ground.

Since the body requires moisture to cool itself, you naturally want to retain as much water as possible. One way we lose or expel moisture is through our mouths when we breathe. Try to breathe through your nose or use a bandana to cover your mouth to trap outgoing moisture.

Stick to carbs and limit protein-rich meals, especially large, filling ones. Protein increases metabolic heat which contributes to warming the body. Also, late-night eating has been linked to elevated night-time core body temperatures so you should avoid late night snacks.

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Preparing for the inevitable

If you believe climate change will grow worse and humans are unprepared for what is coming, it may be a good idea to start acclimating yourself to heat. Turn the thermostat up, to around 74-76 if possible, and let your body begin to acclimate to higher temperatures. This will help reduce the body’s reliance on artificial cooling methods.

Quick note about pets and animals

Don’t forget that animals can overheat too and given their importance in a survival situation, it’s critical to maintain their health too. Make sure they have plenty of water to drink and watch for signs of heat stroke in pets:

  • wide eyes
  • rapid panting
  • hot skin
  • excessive drooling
  • twitching muscles
  • vomiting
  • dazed look