How Extreme Heat Affects Your Body — And Who Faces the Greatest Risk

How Extreme Heat Affects Your Body

Summer heatwaves are more than just uncomfortable — they can be genuinely dangerous. While hot weather poses some level of risk to everyone, certain groups are significantly more vulnerable to serious health consequences. Understanding what heat does to the body is the first step toward protecting yourself and those around you.

What Happens Inside Your Body When Temperatures Rise

As your body temperature climbs, your blood vessels begin to dilate, allowing more blood to flow closer to the skin's surface. This natural cooling response has a side effect: it lowers your blood pressure, forcing your heart to pump harder to keep circulation going.

At the same time, your body ramps up sweat production. As that sweat evaporates from the skin, it carries significant heat away with it — a highly effective cooling mechanism. However, sweating also depletes your body's fluid and salt reserves, and the balance between these two becomes disrupted over time.

Together, reduced blood pressure and fluid loss can trigger a range of symptoms, from minor irritations like heat rash and swollen feet to more serious conditions like heat exhaustion.

Signs of Heat Exhaustion

Heat exhaustion occurs when the body's cooling systems begin to struggle. Common symptoms include heavy sweating, dizziness, nausea, headache, and fatigue. If someone around you shows these signs, move them to a cool environment, offer water, and apply cool, damp cloths to the skin.

If the person does not show improvement within 30 minutes, the situation escalates to a medical emergency. At that point, they may be experiencing heatstroke — and you should call emergency services immediately.

When Heat Becomes Life-Threatening

The human body works hard to maintain a core temperature of approximately 37°C, regardless of external conditions. In extreme heat, however, that balance becomes increasingly difficult to sustain.

Heatstroke occurs when the body's temperature exceeds 40°C and its cooling mechanisms fail entirely. A person experiencing heatstroke may stop sweating despite being dangerously overheated, and can suffer seizures or loss of consciousness. This is a critical medical emergency requiring immediate professional intervention.

If blood pressure falls too severely during any stage of heat illness, the risk of cardiac events — including heart attacks — increases substantially.

Who Is Most at Risk?

While anyone can be affected by extreme heat, certain individuals face a heightened level of danger:

• Older adults may have a reduced ability to regulate body temperature and are more likely to have underlying health conditions.
• Babies and young children cannot effectively communicate distress and are particularly susceptible to overheating.
• People with chronic conditions such as heart disease or diabetes face compounded risks. Diabetes, for instance, can accelerate fluid loss and interfere with the body's ability to sweat.
• Those with neurological conditions like dementia may not recognise heat as a threat or be able to take steps to cool down.
• Less mobile individuals may struggle to move to cooler environments.
• People experiencing homelessness face prolonged sun exposure with limited access to shade or cooling resources.
• Residents of top-floor apartments often deal with higher indoor temperatures due to heat rising through the building.

Medications and Heat: What You Need to Know

Certain commonly prescribed medications can interact dangerously with high temperatures. The NHS advises patients to continue taking their medication as prescribed while placing extra emphasis on staying cool and well-hydrated.

Here's how some medications can become more risky in the heat:

• Diuretics (water pills), often prescribed for heart failure, increase fluid loss — heightening the risk of dehydration and dangerous mineral imbalances.
• Antihypertensives (blood pressure-lowering drugs) can compound the natural drop in blood pressure caused by heat, potentially leading to dangerously low levels.
• Certain epilepsy and Parkinson's medications may inhibit the body's ability to sweat, undermining its primary cooling method.
• Drugs such as lithium and statins can reach unsafe concentrations in the bloodstream when fluid levels drop significantly.

Key Safety Precautions During a Heatwave

Experts from the UK Health Security Agency (UKHSA) recommend checking in regularly on those who may have difficulty staying cool — particularly elderly neighbours, people with underlying health conditions, and those living alone.

Additionally:

• Never leave children, pets, or vulnerable adults in a locked vehicle, even briefly. Temperatures inside a stationary car can soar within minutes.
• Avoid swimming in rivers or open water unless you are confident it is safe — hidden hazards make this especially risky.
• Stay hydrated and avoid excessive physical exertion during peak heat hours.

The Deadly Toll of Extreme Heat

The scale of heat-related harm is starkly illustrated by the summer of 2022 in England, when temperatures reached a record-breaking 40.3°C. That year saw an estimated 2,985 excess deaths attributed to the heat — the highest figure ever recorded in a single year. These numbers serve as a sobering reminder that heatwaves are not simply inconveniences but genuine public health emergencies.

Staying informed, prepared, and attentive to those around you can make a life-saving difference when temperatures soar.