Extreme heat affects human physiology through several interconnected mechanisms. As body temperature rises, blood vessels expand to dissipate heat, a process that lowers blood pressure and forces the heart to work harder. Simultaneously, increased sweating causes the body to lose fluids and salt, disrupting the delicate balance of these substances. Together, these changes can produce symptoms ranging from mild heat rash and swelling to more serious conditions such as dizziness, nausea, fainting, and muscle cramps.
The human body maintains a core temperature of approximately 37C under normal conditions. During hot weather, the body attempts to maintain this temperature through perspiration and increased blood vessel dilation near the skin. However, when temperatures climb significantly, the body’s cooling mechanisms may become overwhelmed. If body temperature exceeds 40C and sweating stops despite continued heat exposure, heatstroke—a medical emergency requiring immediate care—can occur.
Certain populations face disproportionate risk during heat events. Older adults, infants and young children, individuals with chronic conditions such as heart disease or diabetes, and those with limited mobility are particularly vulnerable. Brain conditions including dementia can impair awareness of danger or reduce the ability to take protective action. Additionally, homeless individuals and residents of top-floor apartments may experience greater heat exposure due to environmental factors.
Medications can complicate heat-related health risks. Diuretics increase water loss from the body, exacerbating dehydration risk in high temperatures. Blood pressure-lowering medications can combine dangerously with the body’s natural blood vessel dilation. Some drugs used for epilepsy and Parkinson’s disease inhibit sweating, compromising the body’s cooling capacity. Health authorities recommend that individuals continue taking prescribed medications while prioritizing hydration and staying cool.
Historical data shows significant mortality associated with heat events. During 2022, which recorded the highest temperature in England at 40.3C, approximately 2,985 excess deaths were attributed to heat. The period from early to mid-summer appears to carry particular risk, with increased deaths occurring rapidly—often within the first 24 hours of a heatwave—as people may not have yet adjusted their daily behavior to accommodate extreme conditions.
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