Accidental hypothermia is caused by exposure to cold temperatures resulting in loss of body heat at a rate faster than can be generated by the body. Longer exposures to cold environments are more likely to result in hypothermia than brief exposures. Accidental hypothermia is defined as the unintentional decrease in core body temperature to below 95 degrees Fahrenheit. Accidental hypothermia can be broken down further to primary accidental hypothermia and secondary accidental hypothermia. Primary accidental hypothermia is when a healthy individual is exposed to a cold environment and develops hypothermia (core body temperature less than 95 degrees Fahrenheit). Secondary accidental hypothermia is when the hypothermia is caused by an underlying medical condition or injury, such as cardiovascular or hypovolemic shock. Primary accidental hypothermia most commonly occurs in the winter months and occurs in colder as well as warmer regions of the world and the United States. Infants and the elderly have a greater risk of developing hypothermia if exposed to cold temperatures. Infants are at increased risk of hypothermia due to their higher surface area to body mass ratio. Additionally, infants do not have the ability to shiver in response to the cold or the ability to get out of the cold or apply additional clothing if needed, feeling too cold as adults and children can. Drinking alcohol causes vasodilation, reduces the perception of cold temperatures, may impair decision-making regarding choice of clothing or staying out in the cold for more extended periods, and decreases the body's ability to generate heat (thermogenesis). Hypothyroidism and adrenal insufficiency are medical conditions that increase the risk of hypothermia (primary and secondary). The elderly often have decreased perception of hot and cold temperatures and are often less active or possibly immobilized. The elderly are also more likely to suffer from undernutrition and malnutrition, more likely to have underlying medical conditions that impair internal heat generation in response to the cold. Additionally, individuals with psychiatric illness or dementia have a greater risk of developing primary accidental hypothermia. There are also socioeconomic factors that increase the risk of hypothermia. Some occupations, as well as military service, may involve prolonged exposure to cold environments, as do recreational activities that take place in cold environments, such as skiing and hunting. As the body temperature decreases and hypothermia progresses, affected individuals can experience decreased cognition impairing their ability to make decisions to move to a warmer environment or act in a way to generate heat. Frostbite is classified as a peripheral cold injury. Factors that increase the risk of frostbite are direct contact with cold surfaces such as metal, clothing, or tight-fitting shoes, causing decreased peripheral circulation and medications that cause vasoconstriction.
 

Reference:

Danzl DF. Hypothermia and Peripheral Cold Injuries. In: Jameson J, Fauci AS, Kasper DL, Hauser SL, Longo DL, Loscalzo J. eds. Harrison's Principles of Internal Medicine, 20e. McGraw Hill; 2018.