Heat-Related Health Disorders: How Rising Temperatures Affect Human Bodies

As global temperatures continue to rise due to climate change, heat-related health disorders have become a growing public health concern. The human body is remarkably efficient at regulating its internal temperature, but when environmental conditions overwhelm this delicate system, the consequences can range from mild discomfort to life-threatening emergencies. Understanding how rising temperatures affect human physiology is essential for protecting ourselves and our communities.

How the body regulates temperature 🔗

The human body maintains an internal core temperature of approximately 37°C (98.6°F), regardless of external conditions. This precise regulation is controlled by the hypothalamus, which acts like an internal thermostat. When the body senses rising temperatures, it activates several cooling mechanisms to dissipate excess heat.

The primary methods of heat loss include sweating, where moisture evaporates from the skin surface to draw heat away; convection, where heat transfers to surrounding air; and radiation, where the body releases infrared energy. Blood flow to the skin also increases through vasodilation, allowing heat from the core to dissipate at the body’s surface.

Under normal circumstances, these mechanisms work seamlessly. However, problems arise when the rate of heat gain exceeds the body’s capacity for heat loss. High ambient temperatures, high humidity, and low wind can all reduce the effectiveness of the body’s cooling systems, leading to a dangerous accumulation of internal heat.

The spectrum of heat-related illnesses 🔗

Heat-related conditions exist on a continuum, ranging from mild to severe. Recognising early warning signs is crucial for preventing progression to more dangerous conditions.

Heat edema and heat rash 🔗

On the milder end of the spectrum, heat edema involves swelling of the ankles and feet, typically occurring when standing or sitting for prolonged periods in hot conditions. This results from blood vessel dilation and fluid pooling in the lower extremities.

Heat rash, also known as prickly heat, occurs when excessive sweating blocks sweat glands, causing inflammation and small, itchy blisters. These conditions generally resolve with rest in a cooler environment and keeping the skin dry.

Heat cramps 🔗

Heat cramps are painful muscle spasms that typically affect workers and athletes who sweat heavily during strenuous activity. The condition results from an imbalance of sodium and other electrolytes lost through perspiration. Cramps commonly affect the abdomen, arms, and legs, and may occur during or after physical exertion. Treatment involves resting in a cool place, drinking fluids containing electrolytes, and gentle stretching of affected muscles.

Heat syncope 🔗

Heat syncope refers to fainting or dizziness that occurs during prolonged standing or when rising suddenly from a sitting position in hot environments. Reduced venous return to the heart and decreased brain blood flow cause temporary loss of consciousness. Dehydration and lack of acclimatisation increase susceptibility. Moving to a cool area, lying down, and slowly sipping fluids usually resolves the episode.

Heat exhaustion 🔗

Heat exhaustion represents a more serious condition resulting from excessive loss of water and salt through sweating. Symptoms include headache, nausea, dizziness, weakness, irritability, heavy sweating, and elevated body temperature below 40°C (104°F). Without prompt treatment, heat exhaustion can progress to heat stroke. Treatment involves moving to a cool environment, removing excess clothing, applying cool compresses, and rehydrating with water or electrolyte drinks.

Heat stroke: a medical emergency 🔗

Heat stroke is the most severe and life-threatening heat illness. It occurs when the body’s thermoregulatory system fails completely, causing core temperature to rise above 40°C (104°F) or higher. The sweating mechanism may fail, leaving the body unable to cool itself. Symptoms include confusion, slurred speech, altered mental status, seizures, loss of consciousness, and very high body temperature. Heat stroke can cause permanent disability or death without emergency medical intervention.

Immediate action is critical: call emergency services, move the person to a cool area, remove outer clothing, and begin aggressive cooling using cold water immersion, ice packs to the neck, armpits, and groin, or wet cloths combined with fanning.

Systemic health impacts of heat exposure 🔗

Beyond acute heat illnesses, prolonged exposure to high temperatures can trigger or worsen chronic health conditions across multiple organ systems.

Cardiovascular effects 🔗

Heat stress can exacerbate cardiovascular disease, increasing risks of heart attack, stroke, and dangerous heart rhythm abnormalities. When the body attempts to cool itself, blood vessels dilate and cardiac output must increase to maintain adequate blood flow to both the skin and vital organs. For individuals with pre-existing heart conditions, this additional strain can be overwhelming.

Research has shown that a 1°C rise in temperature increased cardiovascular mortality by over 4% within two days after exposure in older adults. Blood viscosity also increases during heat stress, raising the risk of blood clots and thrombotic events.

Kidney disease and acute kidney injury 🔗

The kidneys are particularly vulnerable to heat stress. Prolonged heat exposure can lead to acute kidney injury through dehydration, electrolyte imbalances, and muscle breakdown. Rhabdomyolysis, a condition where damaged muscle releases proteins into the bloodstream, can occur during intense physical activity in hot conditions and may cause serious kidney damage.

Outdoor workers in tropical climates face heightened risk of chronic kidney disease related to repeated heat exposure and dehydration. Adequate hydration and regular breaks in cool environments are essential preventive measures.

Respiratory and allergic conditions 🔗

Heat waves are often accompanied by poor air quality and increased pollen levels, worsening respiratory conditions like asthma and chronic obstructive pulmonary disease. Heat can also increase the risk of infectious disease transmission and contribute to the spread of allergens that trigger skin ailments and respiratory problems.

Mental health impacts 🔗

Rising temperatures also affect mental wellbeing. Heat can make people confused, anxious, or even aggressive. Studies have documented increases in emergency psychiatric presentations during heat waves, and individuals with pre-existing mental health conditions face elevated risks during extreme heat events.

Who is most vulnerable? 🔗

Heat does not affect everyone equally. Certain populations face significantly greater risks due to physiological, social, or occupational factors.

Older adults 🔗

People aged 60 years and older are consistently the most vulnerable to heat-related illness and death, with 82-92% of excess mortality during heat waves occurring in this age group. Several factors contribute to this vulnerability: the ability to sense heat and respond appropriately diminishes with age; sweat production decreases; cardiovascular responses to heat stress become impaired; and thirst sensation is often reduced, leading to inadequate fluid intake.

Heat-related mortality among people over 65 increased by approximately 85% between 2000-2004 and 2017-2021, highlighting the growing threat as populations age and temperatures rise.

Children 🔗

Children adjust more slowly to temperature changes, produce more heat during physical activity, and sweat less efficiently than adults. Young children depend entirely on caregivers to provide adequate fluids and protection from heat, making supervision critical during hot weather.

People with chronic conditions 🔗

During heat waves, emergency room visits and hospital admissions increase for people with diabetes, cardiovascular diseases, respiratory diseases, and mental health conditions. These conditions can impair the body’s ability to regulate temperature, and certain medications may interfere with sweating, hydration, or cardiovascular responses to heat.

People with diabetes experience impaired blood vessel dilation and may have reduced sweating capacity due to neuropathy, compromising their ability to dissipate heat effectively.

Outdoor workers 🔗

Agricultural, construction, military, firefighting, mining, and manufacturing workers face elevated risks due to occupational heat exposure combined with physical exertion. Protective equipment, while necessary for safety, can create additional barriers to heat dissipation.

Sex-based differences 🔗

Research from the National Institute for Occupational Safety and Health indicates that women may demonstrate different heat tolerance patterns compared to men, potentially related to differences in cardiovascular function, metabolism, and body composition. However, occupational exposure patterns, where men predominate in outdoor manual labour, mean that men currently experience higher rates of occupational heat illness.

The growing threat of climate change 🔗

The frequency and intensity of extreme heat events will continue to rise throughout the 21st century due to climate change. Between 2000 and 2019, approximately 489,000 heat-related deaths occurred annually worldwide, with 45% in Asia and 36% in Europe. In Europe alone, an estimated 61,672 excess deaths occurred during the summer of 2022.

Urban populations face additional risks due to the heat island effect, where buildings, roads, and lack of green spaces cause cities to be significantly warmer than surrounding areas. Combined with ageing populations and increasing prevalence of chronic diseases, the public health burden of heat is expected to grow substantially in coming decades.

Protection and prevention 🔗

The encouraging news is that heat-related illness and death are largely preventable with appropriate precautions. Key protective strategies include staying hydrated by drinking water regularly throughout the day; avoiding strenuous outdoor activity during peak heat hours; seeking air-conditioned environments when possible; wearing loose, lightweight, light-coloured clothing; and checking on vulnerable neighbours and family members during heat events.

Community-level responses, including heat early warning systems and cooling centres, play vital roles in protecting vulnerable populations. Healthcare providers can help by counselling at-risk patients about heat safety and reviewing medications that may affect heat tolerance.

What do you think? As temperatures continue to rise globally, how can communities better protect their most vulnerable members from heat-related illness? What changes have you noticed in your own experience of summer heat over the years?

References

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC2900329/
2. https://www.who.int/news-room/fact-sheets/detail/climate-change-heat-and-health
3. https://www.cdc.gov/niosh/heat-stress/about/illnesses.html
4. https://pmc.ncbi.nlm.nih.gov/articles/PMC4843928/
5. https://my.clevelandclinic.org/health/diseases/22111-hyperthermia
6. https://www.escardio.org/Journals/E-Journal-of-Cardiology-Practice/Volume-22/climate-change-and-cardiovascular-disease-the-impact-of-heat-and-heat-health-a
7. https://pmc.ncbi.nlm.nih.gov/articles/PMC11489510/
8. https://www.who.int/news/item/25-07-2024-united-nations-secretary-general-calls-for-global-action-on-extreme-heat
9. https://www.hopkinsmedicine.org/health/conditions-and-diseases/heatrelated-illnesses-heat-cramps-heat-exhaustion-heat-stroke
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11. https://pubmed.ncbi.nlm.nih.gov/38166501/