Sun stroke is medically referred to as Hyperthermia, which is an elevated body temperature due to failed thermoregulation, or inability to regulate the body's temperature. Effectively, this condition means that your body is either producing or absorbing more heat than it can dissipate. Once your body temperature reaches a temperature, greater than 40.6 C (105.1F) sun stroke becomes a medical emergency. Without immediate treatment you can incur a disability or even die.
The term sun stroke is often used in place of heat stroke. However, heat stroke is an overexposure to heat, no matter whether you are in the sun, in the shade, or indoors. Sun stroke, on the other hand, is caused by overexposure to the sun's radiation. Heat stroke occurs when your body's thermostat cannot keep your body cool. Sun stroke occurs when this happens when the source of the heat is the sun.
An example of sunstroke is when direct radiation to an unprotected head with sparse or no hair cover penetrates the skull and irritates the outer layers of the brain. At the same time, the head overheats if the blood circulation is insufficient to carry the excess heat away. Babies are also at particular risk here, as their skull is still very thin and most have very thin hair cover.
Sun stroke is caused by prolonged exposure to excessive heat from the sun or a combination of heat from the sun and high humidity levels. The heat-regulating mechanisms of the body eventually become overwhelmed and when no longer able to effectively deal with the heat, the body temperature starts to climb uncontrollably.
Exercising in the heat will exacerbate the situation. Significant physical exertion on a very hot day can generate heat beyond a normal healthy body's ability to cool itself, because the heat plus any humidity of the environment reduce the efficiency of the body's normal cooling mechanisms.
There are further factors that will push the body's limits, such as:
Sun stroke without overdoing the exercise side of things, is more prominent with the young or the elderly. ie. they just plain overdo the exposure to the sun. Too long in the sun without protection when it is plainly too hot.
Sun stroke can also be aided and abetted unknowingly through the use of medications that reduce vasodilation, sweating, and other heat-loss mechanisms, such as anticholinergic drugs, antihistamines, and diuretics. Sometimes in this situation, the body's intolerance for excessive heat actually causes heat stroke rather than sun stroke as they become incapable of coping with the heat, even while resting.
Sun stroke actually differs from an ordinary fever which has really high body temperatures in that a fever is caused by a change in the body's temperature set-point. Both require medical attention as if not cooled immediately, the high body temperature will eventually damage the tissue of almost every organ.