However, infants and toddlers, people who are 65 or older, anyone who is overweight and people on certain medications can be at the highest risk for heat-related illnesses, according to the Centers for Disease Control and Precention (CDC). Those illnesses can include heat stroke, heat exhaustion, heat cramps, sunburn and heat rash. According to the CDC, people suffer heat-related illness when the bodys temperature control system is overloaded. In such cases, a persons body temperature rises rapidly. When the humidity is high, sweat will not evaporate as quickly, preventing the body from releasing heat quickly.