Human thermoregulation is essential for maintaining a core body temperature of around 37 °C. In a hot environment, the autonomic nervous system centrally controls this process by regulating vasomotor and sudomotor responses. At the same time, peripheral mechanisms manage skin blood flow and sweat responses across the body. These processes are influenced by heat adaptation. Heat adaptation occurs through heat acclimation in controlled environments or heat acclimatization in natural hot climates. Heat acclimation, achieved through repeated heat exposure, enhances thermoregulation, improves physical performance, and improves thermal tolerance. Heat acclimatization, on the other hand, is an adaptation process that occurs when individuals are exposed to a natural hot environment for an extended period. Heat acclimatization can differ in some ways from the adaptations resulting from heat acclimation and is particularly relevant to people from tropical regions who have lived in hot climates for a long time. Both heat acclimation and heat acclimatization can diminish over time. In the case of heat acclimation, the acclimation benefit can diminish if not maintained through regular heat exposure, which noticeably affects heart rate. Decay in heat acclimatization, particularly the sweating responses, was observed in tropical individuals living in a temperate or colder environment after several months. Physical activity in hot environments challenges physiological and cognitive systems, predominantly impacting the cardiovascular and central nervous systems. The interaction between these systems and external environmental stressors, including elevated temperatures, is crucial in determining performance outcomes. Unlike physical activity in heat, the implications of heat on cognitive functions are nuanced and multifactorial. While certain aspects of cognitive performance seem resilient to heat, others can be detrimentally affected, particularly at specific temperature thresholds or durations of exposure. The body’s adaptive mechanisms, such as neural resource allocation and acclimatization, play significant roles in mediating these effects.