More moisture in the lower atmosphere means perspiration works less effectively and can stymie bodily recovery with warmer nighttime temperatures.

Below is a chart of the Heat Index using the measured air temperature and dew point. As one or the other increases, so does the heat index.

The heat index is a measure of how hot it really feels on your body when relative humidity is factored in with the actual air temperature.

For example, when the air temperature is 100 degrees Fahrenheit, and the relative humidity is 55 percent, the heat index can shoot up to a sweltering 124 degrees Fahrenheit. And that’s in the shade.

You're not imagining it. Humidity really has gotten worse in the last 40 years. As temperatures rise across the U.S., here’s what you need to know about high humidity and how it can affect you.

The humidity also plays a role, making it feel hotter than the actual temperature, called the heat index. This is calculated by using the temperature versus the relative humidity. For example ...