Which of the following can intensify risk of heat-related illness?

Extreme temperatures significantly intensify the risk of heat-related illnesses because they create an environment where the body struggles to maintain a normal internal temperature. When the external temperature rises, the body's mechanisms for heat loss, such as sweating, can become overwhelmed, especially in humid conditions where sweat does not evaporate efficiently. This can lead to heat exhaustion or heat stroke, which are serious medical conditions.

In contrast, indoor environments, while they can be hot, do not inherently increase the risk as significantly unless they are poorly ventilated or lack air conditioning. Proper hydration actually helps prevent heat-related illnesses by enabling the body to regulate its temperature more effectively. High altitudes can contribute to other types of environmental stressors, but they are not directly related to the mechanisms that lead to heat-related illnesses the same way extreme temperatures do. Therefore, understanding the direct impact of extreme temperatures is crucial for managing and mitigating the risks of heat-related health issues effectively.