Making good clothing choices in hot environments can help prevent heat-related illnesses. Clothing made of synthetic fabrics should be lightweight and draw sweat from the skin. The evaporation of sweat will decrease the body's temperature.
The upper body sweats more than the lower half, so wearing clothing that is loose-fitting and allows for more air circulation from the waist up is a good way to transfer heat away from the body.
We lose 50% of our body heat from our scalp and our face. Hats used for sun protection should be designed to allow for good ventilation of the body's heat from the head.
WebMD Medical Reference from Healthwise