In the hot summer months of the southern, subtropical regions, horses endure long-term exposure to heat. Most horses cope with this thermal stress by sweating, which is the natural cooling mechanism of the body. However, in some horses, the sweat glands of the skin are over stimulated for long periods of time. This leads to a refractory state in which they do not produce sweat. The consequence of this is a condition called anhidrosis, which can result in hyperthermia, respiratory distress, and heat stroke.