For centuries, sweat has been understood as the body's most faithful cooling ally — yet Arizona State University researchers have found that in hot, dry, and perfectly still air, the physics of the atmosphere just above the skin can quietly betray that alliance, reducing evaporative cooling by more than half. Two competing air currents — one sinking, one rising — nearly cancel each other out, leaving sweat vapor trapped against the body like a silent siege. The discovery reveals a gap in the heat-safety models that protect workers, soldiers, and the vulnerable, and asks us to reckon with how m