What does hot weather do to the body?

What does hot weather do – Extreme heat can pose significant risks to health, particularly for individuals with specific conditions or those in high-risk groups. While the effects of heat are felt by everyone, some populations are more susceptible to severe consequences. The UK Health Security Agency (UKHSA) highlights that older adults, infants, and young children require heightened vigilance during heatwaves. These groups, along with others like those with chronic illnesses or limited mobility, are more vulnerable due to their bodies’ reduced ability to regulate temperature efficiently.

The Body’s Response to Extreme Heat

When temperatures rise, the body initiates several physiological changes to manage the heat. Blood vessels near the skin expand, allowing more blood to flow to the surface. This process helps dissipate heat but also reduces blood pressure, forcing the heart to work harder to circulate blood. While this can lead to mild symptoms such as discomfort from a heat rash or swelling in the feet, it also increases the risk of more serious issues.

As the body sweats, it loses fluids and essential salts. This loss disrupts the delicate balance of electrolytes, which can trigger heat exhaustion if not addressed. The combination of lowered blood pressure and fluid depletion often results in symptoms like dizziness, nausea, and fatigue. The NHS warns that prolonged exposure to high temperatures can cause core body heat to rise rapidly, pushing the body’s natural cooling systems to their limits.

“The body strives to maintain a core temperature of about 37°C regardless of external conditions,” says the UKHSA. “This is the temperature at which our systems evolved to function, but extreme heat makes it harder to sustain.”

Heat exhaustion, if left unchecked, can escalate to heatstroke—a life-threatening condition. The NHS advises that heatstroke occurs when core temperature exceeds 40°C, often leading to seizures, unconsciousness, or even organ failure. Symptoms include a lack of sweating, even in hot environments, and a dramatic drop in body temperature. Immediate action is critical; cooling the person within half an hour can prevent serious complications, but failure to do so within 30 minutes necessitates emergency medical care.

Medications and Heat Exposure

Drugs can amplify the risks of heat-related illnesses. Diuretics, commonly known as “water pills,” increase fluid excretion and are often used to treat heart failure. In hot weather, they heighten the likelihood of dehydration and mineral imbalances. Similarly, antihypertensives—medications that lower blood pressure—can compound the body’s struggle to maintain stable temperatures. When combined with the vasodilation caused by heat, they may lead to dangerous drops in blood pressure.

Other medications, such as those for epilepsy or Parkinson’s, can block sweating, reducing the body’s ability to cool itself. Lithium and statins, used for mental health and cholesterol management, may also become more concentrated in the blood due to fluid loss, increasing their side effects. The NHS recommends continuing medication as usual but prioritizing hydration and cooling measures to counteract these risks.

Heat-Related Mortality Trends

Historical data reveals alarming patterns in heat-related deaths. In 2022, the UK recorded its highest temperature at 40.3°C, leading to an estimated 2,985 excess deaths. This figure rose to 1,311 in summer 2024 and 1,504 in summer 2025, indicating a growing threat. Most of these deaths are linked to cardiovascular issues, such as heart attacks or strokes, caused by the body’s efforts to stabilize temperature.

Interestingly, the surge in fatalities often begins when temperatures surpass 25°C–26°C. However, research suggests that heat-related deaths are more common in spring or early summer than during peak heat periods. This phenomenon may be attributed to behavioral shifts as the season progresses—people adjust their routines to cope with heat, potentially underestimating the risks. The UKHSA notes that the increase in deaths occurs swiftly, often within the first 24 hours of a heatwave, underscoring the urgency of preventive actions.

Those living in top-floor apartments or without access to cooling systems face heightened exposure. Homeless individuals, too, are particularly vulnerable due to their limited ability to seek shade or shelter. Children, who have smaller body sizes and less sweat production, are also at risk. Additionally, individuals with conditions like diabetes may experience accelerated fluid loss, complicating their ability to manage heat stress.

Heatwaves demand proactive measures to protect at-risk groups. Simple steps such as staying hydrated, avoiding prolonged sun exposure, and monitoring temperature can make a critical difference. The NHS emphasizes that even in high heat, medication should not be stopped unless advised by a healthcare professional. Instead, focus on maintaining cool environments and ensuring adequate fluid intake to support the body’s natural defenses.

Preventive Strategies for Heat Safety

During heatwaves, certain precautions are essential. The UKHSA recommends keeping an eye on individuals who struggle to adapt to high temperatures, including the elderly and those with long-term conditions like heart disease. For example, diabetes can impair the body’s capacity to retain water, while vascular complications may hinder sweating. These factors combine to create a heightened risk of heat-related illnesses.

It is also crucial to avoid leaving vulnerable individuals in locked vehicles. Even in mild weather, temperatures inside a car can skyrocket, leading to rapid dehydration and heatstroke. The NHS advises checking on neighbors, especially those living alone, and ensuring they have access to cooling resources. Public awareness campaigns should highlight hidden dangers in open water, urging people to review warning signs before cooling off in rivers or lakes.

Understanding the body’s limits during heatwaves is vital. While core temperature remains around 37°C, the body’s ability to regulate this temperature weakens as external heat intensifies. This breakdown can lead to a cascade of health issues, from mild discomfort to severe emergencies. By recognizing the signs of heat exhaustion and taking swift action, many of these complications can be mitigated.

As the climate continues to change, the frequency and intensity of heatwaves are expected to rise. This trend underscores the importance of education and preparedness. Whether through adjusting daily routines, staying informed about weather conditions, or supporting at-risk communities, proactive steps can reduce the impact of extreme heat. The NHS and UKHSA stress that knowledge and vigilance are key to preventing heat-related illnesses and saving lives.