Editing Environmental and Public Health (section)

== The Physiological Impacts of Heat Stress ==

Extreme heat is currently one of the deadliest weather-related phenomena globally, and the physiological burden it places on the human body is profound. 

=== Thermoregulation and Cardiovascular Strain ===
Humans maintain a core body temperature of roughly 37°C. When exposed to extreme heat, the autonomic nervous system triggers two primary cooling mechanisms: vasodilation (widening of blood vessels near the skin to radiate heat) and sweating (evaporative cooling). 

Both mechanisms place immense strain on the cardiovascular system. To push blood to the skin's surface, the heart must beat faster and pump harder. For individuals with pre-existing cardiovascular conditions, the elderly, or those taking certain medications, this increased cardiac demand can lead to fatal heart attacks or strokes. Additionally, excessive sweating without adequate fluid replacement leads to severe dehydration, which can precipitate acute kidney injury and eventually renal failure.

=== Wet-Bulb Temperature and Human Survivability ===
The danger of extreme heat is intrinsically linked to atmospheric humidity, a relationship measured by the '''wet-bulb temperature'''. Sweating only cools the body if the sweat can evaporate into the air. If the air is already saturated with moisture (high humidity), evaporation slows or stops entirely.

If the ambient wet-bulb temperature approaches 35°C (roughly 95°F at 100% humidity), the human body can no longer dissipate heat into the environment, regardless of age, health, or hydration status. Under these conditions, core body temperature rapidly rises, proteins begin to denature, and hyperthermia becomes lethal within hours. As global temperatures increase, regions in the Middle East, South Asia, and the tropics are increasingly at risk of crossing these strict physiological thresholds of human survivability.