Which of the following conditions increases the risk of heat-related illnesses?

High humidity levels significantly increase the risk of heat-related illnesses. When humidity is high, the body's ability to cool itself through the evaporation of sweat is compromised. Sweat evaporation is a critical mechanism for regulating body temperature; when humidity is high, the moisture in the air prevents sweat from evaporating efficiently. As a result, the body struggles to release heat, leading to an increased risk of conditions such as heat exhaustion or heat stroke.

Acclimatization to heat, on the other hand, refers to the process by which the body gradually adapts to heat over time, improving its ability to cope with higher temperatures and reducing the likelihood of heat-related illnesses. Moderate temperatures and frequent hydration also play protective roles in preventing heat-related illnesses, as cooler conditions allow for better heat dissipation, and adequate hydration helps maintain physiological functions during hot weather.