What are the absolute limits of human endurance for pain, cold, and heat?

The answer

Human physiological limits are remarkably specific. Core body temperature must stay between 35°C and 41°C - hypothermia begins below 35°C, and brain protein denaturation occurs above 41.6°C. The lowest survived core temperature was 13.7°C, recorded in Anna Bagenholm in 1999 after falling into frozen water for 80 minutes. Humans can survive about 3 minutes without oxygen, 3 days without water, and roughly 3 weeks without food, though Mahatma Gandhi survived 21 days of complete fasting at age 74. The highest recorded survived fever was 46.5°C. Pain tolerance varies 40-fold between individuals due to SCN9A gene variants. At high altitude, consciousness is lost in 15-20 seconds above 13,700 meters without pressurization due to hypoxia.