The reaction that occurs when tissue (usually skin) receives more energy (heat, chemical energy, electrical energy, or radiation) than it can absorb without injury. Factors such as the duration of contact, temperature, volume of chemical, and voltage influence the severity of the injury. The notable pathologic changes are denaturation of protein and coagulation of blood vessels. Local destruction of tissue leads to bacterial invasion and infection; loss of fluid, electrolytes, and protein; loss of temperature control; and pain. Systemic reactions include altered blood flow and temperature regulation, fluid and electrolyte imbalances, shock, infections, and catabolism. Associated problems—other illnesses (particularly cardiopulmonary), trauma, and injuries caused by inhaling carbon monoxide, smoke, and occasionally heat—may be lethal or contribute significantly to mortality and morbidity from burn injuries.