Final answer:
Miliaria rubra, or heat rash, is caused by the blockage of eccrine sweat glands, which are involved in thermoregulation by producing mostly water-based sweat.
Step-by-step explanation:
Miliaria rubra, commonly known as heat rash, is caused by the occlusion of the eccrine sweat glands. These glands are responsible for producing sweat, which is mostly water, for thermoregulation. When these glands are blocked, it results in inflammation and rash. Eccrine glands are present throughout the skin on the body and are particularly abundant on the palms of the hands, soles of the feet, and forehead. Unlike the apocrine glands that are associated with hair follicles and are responsible for a thicker sweat that contributes to body odour, eccrine glands secrete a hypotonic solution that helps to regulate body temperature through evaporative cooling.