Heatwaves affect the body through multiple physiological processes that can range from mild to life-threatening. As temperatures rise, blood vessels expand to dissipate heat, which lowers blood pressure and forces the heart to work harder. This initial response can trigger symptoms such as heat rash or swollen extremities. The body simultaneously loses fluids and essential salts through perspiration, and the disruption in the balance between these elements, combined with reduced blood pressure, can lead to heat exhaustion marked by dizziness, nausea, fainting, confusion, muscle cramps, headaches, and extreme fatigue.
Certain populations face elevated risks during extreme heat events. The UK Health Security Agency identifies older individuals, those with pre-existing medical conditions, and people living alone as particularly vulnerable. Children, individuals with limited mobility, and those experiencing homelessness also face heightened danger. Medical conditions such as diabetes, heart disease, and dementia can compromise the body’s ability to regulate temperature or recognize heat-related danger. Some medications including diuretics, blood pressure reducers, certain epilepsy and Parkinson’s treatments, lithium, and statins can interfere with the body’s cooling mechanisms or become problematic when fluid loss occurs.
Severe heat exposure can progress to heatstroke, a medical emergency characterized by body temperatures exceeding 40C, seizures, and loss of consciousness. Death from heat-related causes typically results from heart attacks and strokes triggered by the strain of temperature regulation. Mortality risk increases once temperatures reach 25C-26C, with evidence suggesting most excess deaths occur within the first 24 hours of a heatwave. Heat-related fatalities may be more common during spring and early summer than peak summer months, possibly because behavioral adaptations develop as warmer seasons progress.
Public health guidance recommends staying indoors during peak sun hours between 11:00 and 15:00, maintaining adequate hydration, seeking shade, using sunscreen, and monitoring vulnerable individuals. Heat exhaustion can typically be reversed within 30 minutes through cooling measures including moving to cool environments, elevating feet, providing fluids, and applying cool water or cold packs. However, failure to improve within this timeframe requires immediate emergency medical attention.
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