What's worse Humid or Dry Heat?

Generally speaking, there are two kinds of heat: dry heat, in which humidity levels are less than 40 percent, and humid heat, which includes 40 percent or higher. Depending on the moisture level in the air, your body will respond differently to the heat. When planning a vacation or working out, you need to account for this change.

Dry Heat:
Since rainfall contributes to humidity levels, locations with little rainfall such as deserts usually have dry type heat. This type of heat doesn't feel nearly as hot as humid heat because the body sweats. When your body sweats under hot conditions, it will evaporate and this process keeps you feeling cooler. Try spraying water on your face in front of a fan during a hot day and you'll feel instant cooling.

With the air being so dry, moisture will evaporate in your body including your mouth and respiratory system which explains the dryness of the mouth. Even though athletes sweat more under humid heat conditions, they feel more thirsty with dry heat because of the evaporation process.

Humid Heat:
Under humid heat conditions there are higher levels of moisture in the air. In areas such as the Eastern part of the USA where the moisture level is higher during the summers, the air feels significantly hotter. Under these conditions, sweat doesn't evaporate very quickly resulting in a lack of evaportion. This results in the body feeling hotter.

There is a unit of measure called the Heat Index which meteorologists use to predict just how hot the body actually feels. Here is how it's used. Let's say the temperature in Las Vegas, CA is 106 deg F and the humidity is only 8%. The resulting Heat Index is 99 DegF. On the other hand, if you're in Washington DC and the temperature is only 91 deg F with a humidity level of 60%, the resulting Heat Index will be 102 deg F. This is 3 degrees hotter than Las Vegas!!

So, the bottom line is to make sure and monitor the humidity and compare the actual temperature with the heat index and you'll have a good idea of what to expect.