People are most comfortable whenever the relative humidity level is around 45 percent says HowStuffWorks. A level of 100 percent humidity means that the air is saturated with water vapor and unable to hold more. When this happens, perspiration cannot evaporate into the air, making people feel hotter.
People are sensitive to humidity, since the skin requires a certain amount of humidity in the air to expel moisture and maintain a comfortable body temperature. Zero percent relative humidity coupled with a temperature reading of 75 degrees Fahrenheit feels like 69 degrees instead. Similarly, 75 degrees with 100 percent humidity feels like 80 degrees.