What Is Heat Index And Staying Cool

With summer in full swing, you may have heard the term "heat index." Not sure what it means? Well, read on about the heat index and ways to stay cool.

Humans naturally have several defense mechanisms to combat overheating but the most important is sweating. When a body sweats, the goal is for the sweat to evaporate. When any liquid evaporates (in this case obviously sweat), heat energy is taken away when converting from a liquid (sweat) to a gas (water vapor). Thus, sweating causes cooling on the skin's surface when the sweat evaporates. 

When someone comments on Las Vegas or Phoenix's heat being a "dry heat" and more tolerable than say, Miami's heat, there is a scientific reason behind that. The more humid an air mass is, or in meteorological terms the higher the dewpoint is, the more difficult it is or slower it takes for water to evaporate and vice versa. Therefore, sweat in a climate such as Phoenix evaporates easily because the humidity and dewpoints are low. The easier/more quickly sweat evaporates, the more heat is whisked away from a human body. In Miami, where the humidity and dewpoints are higher, sweat takes longer to evaporate, so there is a less heat being removed from one's body. Wind also helps sweat evaporate quicker. This is why people use fans to cool off in the summer. 

To take into account the combination of humidity and temperature, a measurement called the heat index is used. Basically, it accounts for how hot it "feels" on a human body by taking into account both the temperature and humidity. A temperature of 110 degrees with very low humidity in Phoenix could feel "cooler" than 95 degrees in very high humidity in Miami. A thermometer can't take into account how humid an airmass is and thus how warm it feels for a human body...but heat index can. 

Of course, there are other ways to keep cool other than sweating. Staying out of the full sun, wearing a hat and light colored clothing and trying to do outdoor activities away from the peak heating of the day between 11 a.m. and 3 p.m. are just some of the ways to try to stay cool. An obvious, but sometimes forgotten, aspect of staying cool is drinking plenty of cool, non-caffeinated and non-alcoholic beverages. An ice-cold glass of water acts in two ways to help cool a body: a) the obvious cooling of an icy fluid in your digestive system helps but more importantly b) it gives your body more fluid to be able to sweat out. When your body gets low on fluids, it naturally conserves fluids for important organs such as the heart, brain and lungs and you sweat less. Sweating less leads to less cooling which then leads to your body being warmer. This is not a healthy cycle for someone trying to stay cool. 

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(Image by Gerd Altmann from Pixabay)