shivering

Shivering is an involuntary muscle contraction that generates heat when your body temperature drops below its set point. Your hypothalamus acts as a thermostat, detecting temperature changes through cold receptors and triggering both shivering and non-shivering heat production. Brown fat provides extra warmth in infants, while shivering during fever occurs because your body's target temperature has been reset upward. Understanding this physiological response reveals how your nervous system maintains the narrow 37°C window needed for survival.

The human body maintains core temperature within a range of less than 1°C (1.8°F) despite external temperatures swinging 60°C or more across seasons, and despite internal heat generation that — in hard exercise — rises to 20 times the resting rate. This precision requires a thermostat, an active cooling system, an emergency heating system, and dedicated fat that burns itself to generate warmth. None of it is conscious. Here is how thermoregulation actually works.

Why do we shiver when cold? Inside the hypothalamus, muscle thermogenesis, brown fat (BAT), fever shivers, and what infants do instead.