Human Thermoregulation in a Heatwave

This simulator models the biophysics of heat stress that drives heatwave mortality: a one-node core-temperature heat balance coupled to a real psychrometric evaporation limit. Dial in air temperature, relative humidity, wind and activity level and watch a 3D body respond — skin flushing as blood vessels dilate, sweat droplets appearing on the skin, and a live core-temperature readout climbing toward the danger zone. The key insight it makes visible: evaporative cooling is capped by how much moisture the surrounding air can absorb, not by how hard the body sweats, so in humid heat sweat keeps flowing while core temperature keeps rising anyway — the physiological mechanism behind heat-exhaustion and heat-stroke deaths in real urban heatwaves.