Final answer:
High humidity inhibits evaporative cooling by saturating the air with water vapor, thus preventing sweat from evaporating quickly and reducing the body's ability to cool itself effectively. The lack of evaporation leads to less cooling and increased body temperature.
Step-by-step explanation:
High humidity prevents effective evaporative cooling because the air is already saturated with water vapor. Evaporative cooling relies on the ability of water to absorb heat as it changes from a liquid to a gas, a process that requires an input of energy known as latent heat. When the relative humidity is high, the air has a reduced capacity to accept more water vapor, which means sweat evaporates more slowly from the skin. As a result, the body's natural cooling mechanism becomes less efficient, making you feel hotter even at the same temperature.
For example, in an environment with high humidity, you might notice that sweat does not evaporate quickly from your body, leaving you feeling sticky and uncomfortable. This is because the difference in water vapor pressure between your skin (where sweat is attempting to evaporate) and the surrounding atmosphere is diminished. Consequently, there is less cooling effect as the latent heat of evaporation cannot be effectively absorbed, leading to a rise in body temperature and discomfort.
Low humidity, on the other hand, may lead to discomfort from the drying out of mucous membranes and the potential increase in respiratory infections due to excessive dryness. Therefore, a balance in humidity is desirable for both comfort and health.