Heat waves trigger a cascade of physiological stress on the human body. Core temperature rises as the environment overwhelms the body's cooling mechanisms, forcing the heart to work harder to push blood toward the skin for heat dissipation. Dehydration accelerates when sweat production increases, depleting electrolytes and reducing blood volume. This combination strains cardiovascular and nervous systems alike.
Vulnerability varies sharply by population. Older adults lose sweat-gland efficiency and suffer blunted thirst responses, making dehydration silent and deadly. Young children cannot regulate temperature as effectively. People with chronic conditions like diabetes, heart disease, and respiratory illness face compounded risk. Those taking certain medications, including diuretics and antipsychotics, experience impaired heat tolerance. Low-income communities without reliable air conditioning bear disproportionate exposure.
Heat exhaustion emerges first, signaled by heavy sweating, weakness, dizziness, and nausea. Without intervention, the body progresses to heat stroke, where sweating actually stops and core temperature spikes above 40 degrees Celsius (104 Fahrenheit). Heat stroke is a medical emergency. Brain damage, organ failure, and death follow within hours if untreated.
The body's thermoregulation system has limits. Once ambient temperature matches skin temperature, evaporative cooling becomes the only mechanism left. High humidity blocks evaporation. Sustained heat without relief exhausts the system entirely.
Prevention requires hydration, shade-seeking, and reduced exertion during peak heat hours. Those at highest risk need active monitoring and air-conditioned refuge. Urban heat islands, where concrete and asphalt absorb and radiate heat, concentrate danger in cities. Climate change lengthens heat seasons and intensifies peak temperatures, expanding both the duration and severity of heat stress across populations.