What can hinder the body's ability to cool down through sweat evaporation?

The body's cooling mechanism through sweat evaporation is significantly impaired by high humidity. When the humidity level is high, the air is already saturated with moisture, which reduces the evaporation rate of sweat. Evaporation is a key process for thermoregulation as it dissipates heat from the body. If the air is too humid, the sweat cannot evaporate effectively, leading to an increased risk of heat-related illnesses, such as heat exhaustion or heat stroke.

High air temperature, while it also poses a challenge, primarily affects how much heat the body generates and the gradient needed for effective evaporation, but it is the high humidity that directly prevents sweat from evaporating efficiently. Low fitness level and insufficient clothing may influence overall comfort and thermoregulation, but they do not have as direct an impact on the evaporation process as high humidity does.