Exposure injuries arise in extreme environmental conditions. The exposure of the human body to cold temperatures, either alone or in combination with wind, immersion in cold water, or the existence of snow and ice is the mechanism for the commonly understood exposure injuries of frostbite and hypothermia.
Exposure to warm temperatures, often in combination with significant humidity, can cause heat injuries, including hyperthermia, which has three progressive components: heat cramps, heat exhaustion, and heat stroke. Significant exposure of unprotected skin to direct sunlight may also cause sunburn, a condition arising more commonly, but not exclusively, in warm weather environments.
Cold weather is commonly defined as an air temperature of 40°F (4°C) or below. Cold weather exposure injuries in athletes usually occur in circumstances when there is a prolonged exposure to the effects of the elements in sports such as cross-country skiing or mountain climbing. In these instances, even when the participant has taken the precautions as proper clothing and footwear, the physical systems are worn down through a combination of exertion and the elements. In cold weather conditions, the athlete will be required to produce energy for the sport, as well as the body generating sufficient energy to remain warm. When the athlete becomes dehydrated due to exertion, or when the thermal (warming) qualities of protective clothing are reduced due to the accumulation of perspiration next to the skin, the body will not function at its optimal level. In response to the threat of the cold, the blood vessels constrict, and body heat is lost. In such circumstances, when the body temperature falls from its normal 98.6°F (37°C) to less than 95°F (35°C), the body enters into the condition known as hypothermia, when it is unable to warm itself. If a victim is not provided immediate care, hypothermia is a fatal condition.
External factors that may contribute to the onset of hypothermia are a previous exposure to cold injury, as well as the presence of alcohol in the cardiovascular system.
Hypothermia may also occur in circumstances when the air temperature is not within the cold weather range. When a sailor is subjected to spray from the water surface that is very cold (below 40°F [4°C]), or more commonly, when the sailor falls overboard and is immersed in water that exposes the body to a surrounding temperature that mimics the cold weather environment. Hypothermia can occur within 10 minutes of exposure to cold water, and often more quickly if the victim is fatigued.
Air temperatures in cold weather must be further considered with respect to the wind chill factor, the relationship between wind velocity and actual impact upon the human skin. As a general proposition, the greater the wind velocity, the more pronounced the effect of cold on exposed skin. Exposure of inadequately protected skin to cold air, or cold air made more pronounced in its effect due to wind, may lead to frostbite, which is a freezing of the outer skin and the two subcutaneous layers. The most typical body parts to be injured through frostbite are the extremities, including nose, ears, cheeks, fingers, and toes. When caught at an early stage, and the body parts gently warmed in a protected environment, the affected areas can be restored; in severe cases, cell death in the tissue will result and the tissue (or limb) must be removed.
The mechanisms of hyperthermia and its components are tied directly to the effects of dehydration on the cardiovascular system. When the fluid levels of the body become depleted, typically due to the generation of perspiration and minerals, chiefly sodium, the fluid levels of the bloodstream are correspondingly reduced. Lower blood volumes lead inevitably to an inability of the body to generate energy in response to performance or training requirements. In its early stages, which are manifested through the symptoms of heat and muscle cramping, hyperthermia is treated by fluids and rest. In its more pronounced stages, hyperthermia represents potentially fatal consequences.
Sunburn is perhaps the most common exposure injury. It is caused by overexposure to the ultraviolet rays that form a part of sunlight. Individual susceptibility to sunburn is varied; factors such as skin pigmentation, age, and genetics all play a role. Mild cases of sunburn are generally not believed to be serious by themselves; there is significant scientific study in support of the theory that the effects of sunburn are cumulative; prolonged exposure of unprotected skin to the sun is a proven cause of skin cancer. Athletes who compete in disciplines where they are often exposed to direct sunlight are particularly at risk, including cold weather athletes; ultraviolet rays persist in sunlight irrespective of temperature, and solar effects are often deceptive when the air temperature is low.