Weather reporters constantly refer to the "relative humidity." This is a reference term that cites the amount of water vapor in the air compared to the amount the air could hold at a given temperature and location. Warm air has a greater capacity to hold moisture than cold air. It is measured by a weather instrument called a hygrometer. The degree of wetness or dryness is expressed by a percentage figure, which indicates the amount of moisture required in the air for saturation at a specific temperature. Thus, if the air has only half the amount of vapor the relative humidity is 50 percent. Complete saturation of the air is 100 percent, which is a rarity unless it is raining.
"It's not the heat, it's the humidity." This is a true statement made by most people when their bodies tend to feel the damp heat in the air, which can make them listless and uncomfortable. When the air, laden with high humidity, becomes sticky the skin's pores open and the body tends to perspire more freely. Insects are attracted to body sweat and this becomes a major concern when their biting and feeding enable them to transmit diseases.
People who must cope with excessive heat and humidity can easily become irritable, short-tempered, and lose their appetites. Workers and others required to spend many hours out-of-doors during the hottest months of July and August (sometimes referred to the "dog days of summer") can lose a considerable amount of weight by sweating. On the other hand, even higher temperatures with much less moisture content in the air afford greater ease in functioning and a greater tolerance for the drier heat. Yet, people prefer one or the other weather situation depending upon what their own body feels--their physical sensation-- frequently referred to as the sensible temperature.