The human body is an intricate machine designed to maintain a stable internal temperature, a process known as thermoregulation. This finely tuned balance, or homeostasis, is constantly challenged by the external environment. When an individual states they do not “get cold,” it signals a difference in their physiological response or perception compared to others. The reasons for this variance are complex, rooted in the efficiency of internal heat production, the effectiveness of physical insulation, the speed of circulatory control, and long-term biological adjustments.
Metabolic Rate and Internal Heat Generation
The foundation of cold tolerance lies in the body’s Basal Metabolic Rate (BMR), which represents the energy expended to sustain basic life functions at rest. A higher BMR inherently translates to a greater production of heat, effectively making the body’s core furnace burn hotter. This internal heat generation is the primary defense against a drop in core temperature, supplying warmth before the body must resort to more drastic measures.
Beyond general metabolism, a specialized process called non-shivering thermogenesis (NST) plays a significant role in generating heat without muscle movement. This is accomplished by Brown Adipose Tissue (BAT), a unique type of fat cell packed with mitochondria. BAT contains a protein called uncoupling protein 1 (UCP1) that allows mitochondria to burn stored energy, typically fats, to produce heat directly instead of adenosine triphosphate (ATP).
Individuals with a greater volume of active BAT, often located in the neck and upper chest, can generate a substantial amount of internal warmth upon cold exposure. This rapid, internal heat source contributes significantly to a higher overall cold-induced thermogenesis and a reduced feeling of cold discomfort. Prolonged exposure to mild cold can “recruit” BAT, increasing its metabolic capacity and improving the body’s ability to produce heat without shivering.
Body Composition and Physical Insulation
Physical structure contributes significantly to how the body manages heat loss. Subcutaneous fat, or White Adipose Tissue, acts as a layer of physical insulation, possessing a lower thermal conductivity than lean muscle tissue. This layer slows the rate at which heat moves from the warmer core to the cooler skin surface and the external environment. Individuals with a thicker layer of subcutaneous fat experience a lower rate of heat loss and feel less cold, especially in water or still air.
Another factor is the surface area to volume (SA/V) ratio, a fundamental principle applied to biology. Heat loss occurs primarily at the surface of the skin, while heat is generated throughout the body’s volume. Larger individuals tend to have a lower SA/V ratio, meaning they have less skin surface relative to their heat-generating volume.
This lower ratio results in slower cooling compared to smaller individuals, who must generate more heat just to maintain the same core temperature. Consequently, a person with a larger body mass may lose their metabolic heat more slowly, contributing to a perception of greater cold tolerance.
The Role of Circulatory Adaptation
The body’s immediate control system for cold is managed by the autonomic nervous system through the process of vasoconstriction. When the body detects a drop in temperature, the hypothalamus triggers the narrowing of peripheral blood vessels, especially in the extremities. This action reduces blood flow to the skin and shunts warm blood toward the core organs, limiting heat transfer to the environment and conserving core temperature.
Individual differences in the speed and intensity of this vasoconstrictive response determine how quickly and effectively a person conserves heat. A person with a more robust or earlier-onset vasoconstriction retains core heat more successfully and perceives less peripheral cold discomfort. This response increases the thermal insulation provided by the body’s shell, which includes the skin and subcutaneous fat.
If the core temperature continues to drop despite maximum vasoconstriction, the body initiates shivering as a last-resort mechanism to produce heat through rapid, involuntary muscle contractions. The core temperature threshold for shivering is typically about one degree Celsius below the threshold for vasoconstriction. People who rarely feel cold may have a lower or delayed shivering threshold, indicating their other thermoregulatory defenses are highly effective or that their body tolerates a lower core temperature before reacting.
Long-Term Acclimation to Cold
The ability to withstand cold is not solely innate but is influenced by repeated, non-injurious exposure to low temperatures, a process known as cold acclimation. This long-term adjustment shifts the body’s physiological set points, improving its thermal efficiency over time.
One common adaptation is metabolic acclimation, where chronic cold exposure leads to an increased capacity for non-shivering thermogenesis, often by enhancing the activity and volume of Brown Adipose Tissue. This metabolic shift means the body can produce more heat without relying on the energy-intensive process of shivering. Studies have shown that a few weeks of daily cold exposure can increase the volume of active BAT and reduce the intensity of shivering required to maintain body temperature.
Another form of adjustment is insulative acclimation, which involves a change in the circulatory response. Individuals who undergo this type of acclimation may exhibit a blunted or delayed vasoconstriction, allowing their skin temperature to remain warmer with less discomfort. This allows for better manual dexterity in the cold and reduces the sensation of pain, even as their core temperature is maintained by a heightened metabolic rate.