<P> Relative humidity is normally expressed as a percentage; a higher percentage means that the air--water mixture is more humid . </P> <P> Climate control refers to the control of temperature and relative humidity in buildings, vehicles and other enclosed spaces for the purpose of providing for human comfort, health and safety, and of meeting environmental requirements of machines, sensitive materials (for example, historic) and technical processes . </P> <P> Humans are sensitive to high humidity because the human body uses evaporative cooling, enabled by perspiration, as the primary mechanism to rid itself of waste heat . Perspiration evaporates from the skin more slowly under humid conditions than under arid . Because humans perceive a low rate of heat transfer from the body to be equivalent to a higher air temperature, the body experiences greater distress of waste heat burden at high humidity than at lower humidity, given equal temperatures . </P> <P> For example, if the air temperature is 24 ° C (75 ° F) and the relative humidity is zero percent, then the air temperature feels like 21 ° C (69 ° F). If the relative humidity is 100 percent at the same air temperature, then it feels like 27 ° C (80 ° F). In other words, if the air is 24 ° C (75 ° F) and contains saturated water vapor, then the human body cools itself at the same rate as it would if it were 27 ° C (80 ° F) and at 20% relative humidity (an unstated baseline used in the heat index). The heat index and the humidex are indices that reflect the combined effect of temperature and humidity on the cooling effect of the atmosphere on the human body . </P>

The effect of more relative humidity on human health is
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