What regulates body temperature? Thermoregulation is the process of the body trying to achieve and maintain its optimal temperature. When your body gets too hot or cold, it results in hyperthermia and hypothermia, respectively. Thermoregulation is influenced by heat transfer via convection, conduction, radiation and evaporation. It is also influenced by basal metabolic rate. All of these factors come into play as your body works towards temperature regulation.

The human body tries to maintain a relatively constant core temperature in hot and cold conditions. This biological mechanism is called thermoregulation. An average person has a core temperature of 97 to 100 degrees Fahrenheit.

When the body's ability to thermoregulate becomes disrupted, it can result in overheating or being too cool. Both conditions are potentially life-threatening.

Hyperthermia occurs when the body can no longer release enough of its heat to maintain a normal temperature. A core temperature above 101 degrees Fahrenheit can lead to heat exhaustion, which makes you feel weak and dizzy. A core temperature above 104 degrees Fahrenheit can lead to stroke and death.

Conversely, hypothermia happens when the human body loses heat faster than it can produce heat. Hypothermia occurs as the body temperature falls below 95 degrees Fahrenheit. Like hyperthermia, it can be life-threatening.

The human body regulates temperature by keeping a tight balance between heat gain and loss. The energy balance of a human must account for the heat transfer from the body core to the skin surface and between the skin surface and the ambient environment. There are four mechanisms of heat transfer: convection, conduction, radiation, and evaporation.

Convection is the amount of energy transferred by moving air. This is what causes a “wind chill” when it is cold and windy at the same time. The use of a fan to cool off the body is another good example of convection.

Conductive heat loss happens through physical contact with another object or body. For example, sitting on a metal chair feels cold, because the heat from your body is transferred to the cold chair. If you hold a glass of ice water, the heat from your skin will warm the glass and melt the ice. When it’s cold outside, you might hold a hot cup of coffee to warm you up.

Radiation can both cool and heat the human body without physical contact. In the summer, direct solar radiation is a major contributor to the energy inflow to the body, that’s why it feels much warmer in the Sun than in the shade. Conversely, the body emits longwave radiation into the environment when it is cold.

Evaporation is heat transfer through converting water to gas. Evaporation from sweating is the human body’s biggest heat-sink, but the rate at which evaporation occurs depends on the relative humidity— the more humid a place is, the less evaporative cooling is possible.

The heat gain or loss from the human body is also influenced by the body’s internal heat production. The basal metabolic rate is the amount of energy needed for normal, daily activity, for example, to keep the heart beating and the lungs breathing. In addition, the body produces heat while working or exercising.

In summary, the energy budget of the human body can be described by the fundamental human energy balance equation: S = M - W - R - C - K - E where S represents the rate of internal heat storage; M is the heat production by metabolism; W is the external work rate or heat produced by the human body while performing activities; R, C and K represent heat transfer by radiation, convection, and conduction, and E is heat exchange through evaporation.