Heat, infrared and the body's response
Thermogenesis
Thermogenesis is the body producing its own heat through metabolism: basal metabolism, shivering, brown fat and the cost of digesting food. A sauna does the opposite — it heats you from outside, so the body suppresses heat production and switches to shedding heat instead.
Also called heat production, non-shivering thermogenesis, diet-induced thermogenesis
Every chemical reaction in the body wastes some energy as heat, and at rest that is enough to keep a person at 37 °C. On top of that baseline sit three regulated forms:
- Shivering thermogenesis — involuntary muscle contraction generating heat in the cold.
- Non-shivering thermogenesis — chiefly brown adipose tissue, where the protein UCP1 uncouples mitochondrial respiration so that energy is released as heat rather than captured as ATP.
- Diet-induced thermogenesis — the metabolic cost of digesting, absorbing and storing food.
Thermogenesis and a sauna session. Thermogenesis is heat made by the body. A sauna applies heat to the body. The accurate description of a sauna session is passive heating, and the body’s response is thermoregulatory heat loss — sweating and skin vasodilation — alongside active suppression of its own heat production.
Metabolic rate does rise a little during heat stress, mostly because the heart works harder and because reaction rates rise with temperature. That is a modest effect.
Why it matters here
The word turns up in sauna material. Knowing that a sauna heats you from the outside, rather than making your body produce heat, explains why the body's response in a session is to sweat and shed heat.