thermoneutral

Thermoneutral refers to a state or an ambient temperature range in which an endothermic animal does not need to expend extra energy to maintain a constant core body temperature. In this range, heat production by metabolism roughly matches heat loss to the environment, so the metabolic rate remains at a minimum and does not rise with small changes in ambient temperature.

The concept is commonly described in terms of the thermoneutral zone (TNZ), the temperature window bounded by a lower critical temperature and an upper critical temperature. Within the TNZ, the body can keep its core temperature without activating energy-intensive thermoregulatory responses such as shivering or sweating. Outside the TNZ, physiological mechanisms are engaged to conserve or dissipate heat, including vasomotor adjustments, shivering, non-shivering thermogenesis, sweating, and changes in breathing rate.

The exact boundaries of the TNZ vary among species and individuals and depend on factors such as clothing or insulation, activity level, humidity, air movement, body composition, age, health, and reproductive status. For humans, estimates of the TNZ in air for resting, minimally clothed individuals are often cited in a broad range around the mid-20s to low-30s Celsius, though individual conditions can shift this window significantly.

Applications of the thermoneutral concept appear in physiology and medicine, including the study of energy expenditure, metabolic health, anesthesia management, and animal welfare. Understanding the TNZ helps explain why small environmental changes can have disproportionate physiological effects outside the neutral range.