It's a well-known fact that the body retains more heat when the weather is hot and humid than it does during a drier but equally warm day. As a response to excessive heat in the surrounding environment, our bodies perspire to make us feel cooler.
Evaporation works best when the air is dry.
In moist, saturated air, perspiration cannot evaporate as readily. The combination of excess heat and moisture will cause us to feel hot and sticky. As a rule of thumb, the higher the humidity, the greater the discomfort. Relative humidity Relative humidity is the amount of moisture that the air contains compared to how much it could hold at a given temperature. A figure of 100 per cent would mean that the air has become saturated.