During periods of elevated temperatures, the human body undergoes physiological changes to maintain its core temperature of approximately 37C. Blood vessels expand to increase heat loss to the surrounding environment, while sweating increases to cool the skin through evaporation. However, these protective mechanisms come with consequences: blood vessel dilation lowers blood pressure, forcing the heart to work harder, while sweating causes loss of fluids and electrolytes.
Certain populations face heightened vulnerability during heatwaves. Older individuals, babies, young children, people with chronic conditions, those living alone, and persons with reduced mobility are at elevated risk. Specific medical conditions increase susceptibility, including diabetes, which causes more rapid water loss, and heart disease. Some medications compound the danger: diuretics increase fluid expulsion; blood pressure medications can cause dangerous pressure drops when combined with natural vasodilation; certain epilepsy and Parkinson’s treatments inhibit sweating; and drugs like lithium and statins become more concentrated during dehydration.
Heat exhaustion develops when blood pressure drops sufficiently, producing symptoms including dizziness, nausea, fainting, confusion, muscle cramps, headaches, excessive sweating, and fatigue. If body temperature exceeds 40C, heatstroke—a medical emergency—may occur, characterized by cessation of sweating despite excessive heat, seizures, or unconsciousness. The UK Health Security Agency recommends protective measures including staying indoors during peak sun hours between 11:00 and 15:00, maintaining hydration, using high-SPF sunscreen, and monitoring vulnerable individuals.
Historical data indicates significant mortality during extreme heat events. During 2022, which recorded England’s highest temperature at 40.3C, approximately 2,985 excess deaths occurred. Summer 2024 saw an estimated 1,311 heat-associated deaths, while summer 2025 recorded approximately 1,504. Most heat-related deaths result from heart attacks and strokes caused by cardiovascular strain. Evidence suggests mortality increases dramatically within the first 24 hours of a heatwave and begins when temperatures exceed 25C-26C, with spring and early summer peaks potentially reflecting greater vulnerability before population acclimatization occurs.
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