Isothermia

Isothermia is the condition in which the temperature of an object, region, or system remains constant or varies only within a narrow range, so that its thermal state is effectively uniform with respect to its surroundings. The word combines Greek roots isos (equal) and thermia (heat). In practice, isothermia is often used interchangeably with isothermal or isothermic conditions, though some fields prefer those terms to describe constant-temperature processes more precisely.

In physics and engineering, isothermal means that temperature is kept constant while other variables may change, such as pressure or volume. Real-world implementations rely on heat exchangers, insulation, and active temperature control to maintain stable temperatures in chemical reactors, laboratories, or electronic devices. In earth and atmospheric sciences, isotherms are lines on maps that connect points of equal temperature; the broader idea of isothermia can describe zones where temperature variation is minimal.

In biology and medicine, isothermia can refer to maintaining a stable body temperature in a patient, with normothermia meaning a normal, non-hypothermic range. In surgical and critical-care settings, targeted temperature management aims to preserve or restore isothermia to reduce metabolic stress after injury or cardiac arrest. Isothermia is also used in veterinary, veterinary research, and tissue-preservation contexts to describe controlled thermal conditions for biological material.

See also: isothermal, isotherm, thermoregulation, normothermia, hypothermia, hyperthermia.