Core Temperature Limit: ~42°C (107.6°F) The human body functions optimally at a core temperature around 37°C (98.6°F). A core temperature above 42°C can cause organ failure, brain damage, and death if not cooled quickly.
Heat Stroke Threshold Prolonged exposure to high heat can lead to heat stroke — a medical emergency where the body can no longer regulate its temperature. This typically happens when core body temperature exceeds 40°C (104°F).
Humidity Intensifies Heat Risk High humidity makes it harder for sweat to evaporate, impairing the body’s cooling system. In conditions of 100% humidity, even temperatures around 35°C (95°F) can become fatal.
Wet Bulb Temperature Danger Zone: ~35°C (95°F) The “wet-bulb temperature” combines heat and humidity. A wet-bulb temp of 35°C is considered the upper limit of survivability — beyond this, the human body can no longer cool itself effectively.
Sauna Tolerance: Up to ~100°C (212°F) People can endure extremely high air temperatures (like in saunas) for short periods, especially if humidity is low. However, prolonged exposure is dangerous and can lead to collapse or death.
Dehydration Risk In extreme heat, the body loses water rapidly through sweat. Severe dehydration impairs thermoregulation and can cause heat exhaustion or heat stroke within hours.
Clothing and Environment Matter Dark clothing, lack of airflow, and enclosed spaces can trap heat and raise body temperature faster. Proper clothing and ventilation are crucial for heat dissipation.
Individual Factors Play a Role Age, fitness level, hydration, medical conditions, and acclimatization affect how much heat a person can tolerate. Young children, elderly people, and those with chronic illnesses are more vulnerable.