The testicles hang outside the body because the enzymes required for sperm and testosterone production (in Leydig and Sertoli cells) denature at core body temperature (37°C).

• The Bull Study: Leydig cells (which produce Testosterone) are extremely heat-sensitive. As shown in animal models, artificially raising scrotal temperature by just ~3°C for 48 hours resulted in 90% less testosterone in the blood.
• The Sitting Tax: While a healthy scrotal temperature is ~34.2°C, it can rise up to ~36.5°C (near core body temp) simply while sitting in a car or at a desk.
• Actionable Steps: Ventilate frequently, move to dissipate heat, wear boxers, and sleep cool. Keep 'em cool to protect hormonal output.