This time of year, you hear a lot about the heat index, that number that supposedly incorporates the humidity into a "feel-like" temperature. There is some good science behind this idea, but also a few things you should keep in mind when interpreting it.

Our bodies release heat by perspiring - water on the skin evaporates, taking some energy from the body. The more water vapor in the air, the less evaporation occurs, so discomfort and stress go up in humid weather. But in really dry weather, evaporation from the skin actually increases, so it's also possible for the heat index to be lower than the air temperature, something that's rarely mentioned but occasionally even happens around here.

In addition, factors other than heat and humidity also affect how you feel. These include the color, fabric, and thickness of your clothes, whether the wind is blowing, and whether you're in direct sunlight, none of which the heat index take into account.