You wake up in the morning and head to work or begin your usual daily activities. But the day feels different; the temperature is noticeably high.

At first, it may seem like familiar discomfort: hot skin, sweat gathering on the forehead, increasing thirst, and a slightly faster heartbeat.

You may wonder: Is what I am feeling simply a normal response to heat, or could it be the beginning of heat stress? And can it progress to heatstroke?

When I began researching the question, I discovered that the answer was more complicated than it first appeared. The human body does not experience heat simply as a number on a thermometer. It is constantly trying to maintain a balance between the heat it produces or gains and the heat it can lose. Temperature regulation is a homeostatic feedback system that works continuously to keep deep body temperature within a relatively narrow range. (1)

That became the starting point of my scientific reporting: What happens inside our bodies when temperatures rise? And when do the body’s natural cooling mechanisms become insufficient? I began by reviewing medical and scientific literature and then spoke with Dr. Firas Awawdeh, an emergency and general physician, to examine some of the medical aspects from a clinical perspective.

In this report, I follow the journey of heat through the human body — from the first drop of sweat to the point at which heat loss may no longer be sufficient, and eventually to severe conditions in which excessive heat can contribute to injury involving multiple organs.

Thermoregulation is not a switch that is turned on once. It is a continuous feedback system that helps maintain internal body temperature despite changes in the environment and increases in metabolic heat production. (1)

When thermal load increases, the body activates several responses, including increased blood flow to the skin and sweating.

The ability to cope with heat depends on a complex interaction between the environment and the body. Air temperature, humidity, air movement and thermal radiation interact with physical activity, clothing, body characteristics, age, health status and heat acclimatization to determine how much heat the body gains and how effectively it can lose it. (1)

Increasing blood flow to the skin is not a minor detail. Heat stored in deeper tissues has to be transported toward the skin before some of it can be transferred to the environment. Cutaneous vasodilation therefore increases blood flow to the skin and supports heat dissipation. (1)

At the same time, the sweat glands begin to work. But there is a detail that can be misleading:

A person may sweat heavily on a very hot day and still continue to gain heat. The reason is that the cooling effect of sweating depends largely on the evaporation of sweat from the skin. When water changes from liquid to vapor, heat is removed from the body’s surface.

This means that the effectiveness of sweating depends not only on how much sweat the body produces, but also on whether the surrounding environment allows that sweat to evaporate. High humidity can reduce the efficiency of evaporation, while air movement, thermal radiation, clothing and physical activity also influence heat loss. (1)

For more blood to reach the skin, the cardiovascular system has to adapt. A review of cardiovascular responses to passive heat stress reports that cardiac output can increase up to twofold during heat stress, largely through an increase in heart rate and changes that help maintain blood flow for heat dissipation. (2)

But the body faces another problem at the same time: Sweating causes water loss. As heat exposure continues, the volume of fluid available to the circulation can decline. The cardiovascular system must therefore deal with two demands at once: supporting blood flow to the skin to help dissipate heat while maintaining adequate circulation for the rest of the body. (2)

The heart is no longer responding to heat as a secondary problem. It has become part of the cooling process itself.

Sweat is one of the body’s important tools for losing heat, but it comes at a cost: the loss of water and electrolytes. This brings the story to an organ that is not usually visible in the image of a sweating person: The kidneys.

The kidneys play an important role in water and electrolyte regulation as well as cardiovascular control during heat stress. Evidence reviewed by Chapman and colleagues indicates that the kidneys may face an increased risk of pathological events, including acute kidney injury, during heat stress, with the risk compounded by dehydration and exercise. (3)

What began as drops of sweat on the skin can therefore become, with prolonged heat exposure and dehydration, a challenge involving fluid balance, circulation and kidney function.

This is where scientific information meets a human experience. Construction worker Majdi Khalil, from Nablus, describes an episode in which he experienced severe symptoms while working in hot conditions.

Khalil says he woke up late one day and went to work as usual, but had not eaten or drunk anything before leaving. While working, he developed a headache, followed by nausea, blurred vision and severe dizziness, to the point that he nearly lost consciousness.

He says his colleagues helped him down from a ladder. At first, he expected the symptoms to improve, but they became worse over approximately ten minutes. He then experienced additional symptoms, including a rapid heartbeat, confusion and difficulty speaking.

According to his account, his colleagues took him to hospital, where he says his condition was considered related to heat exposure.

This account does not by itself establish a specific medical diagnosis. It does, however, illustrate how symptoms associated with heat exposure can progress from fatigue and thirst to more serious symptoms requiring medical assessment.

It is easy to reduce the story to a number displayed on a thermometer. But the human body does not respond to air temperature alone.

In heat physiology, heat stress describes the thermal load imposed on the body, while heat strain refers to the physiological response to that load.

The distinction matters. A person is exposed not only to air temperature but to a combination of conditions that determine how much heat the body gains and how much it can lose. Temperature, humidity, air movement, radiation, clothing, physical activity, duration of exposure and heat acclimatization all influence this balance. Individual characteristics, including age and health status, can also affect the response. (1)

That is why there is no single temperature at which the level of danger is identical for everyone.

The more precise questions are: How much heat is the body gaining? How much can it lose? And how long can it continue compensating?

The body can compensate only to a certain point. When the amount of heat gained becomes greater than the amount of heat the body can dissipate, thermal balance begins to fail.

At first, the body’s familiar cooling mechanisms continue:

• The skin vessels dilate.
• Sweating continues.
• The kidneys respond to changes in water, electrolytes and circulation.
• The heart works harder to support circulation and heat dissipation.

But if the thermal load continues and heat loss is no longer sufficient to maintain balance, internal body temperature begins to rise.

This is the turning point in the story: The body is no longer simply trying to keep us comfortable in the heat. It is trying to prevent its internal temperature from reaching dangerous levels.

In severe cases, the effects of heat are no longer limited to sweating, thirst and an increased heart rate. The central nervous system becomes one of the major sites of concern.

Neurological dysfunction is a defining feature of heatstroke and can include confusion, delirium, seizures and altered consciousness.

A 2024 review examining heatstroke-related brain injury describes several mechanisms that may contribute to neurological damage, including disruption of the blood-brain barrier, inflammation, oxidative stress and cellular injury. (4)

This makes clear why heatstroke cannot simply be reduced to the statement: “The body became too hot.”

Heatstroke is the most severe form of heat-related illness and is a medical emergency.

Medical literature commonly describes heatstroke as severe elevation of core body temperature, often above 40°C, accompanied by acute central nervous system dysfunction. Severe cases can involve injury to multiple organs. (4, 5)

But the number alone does not tell the whole story. The problem is not simply that the body has reached a high temperature. It is that the mechanisms responsible for maintaining thermal balance have become overwhelmed, accompanied by neurological dysfunction and potentially systemic injury.

Recent research describes heatstroke as involving interacting processes such as systemic inflammation, oxidative stress, endothelial injury and coagulation abnormalities, alongside neurological and other organ damage. (5)

The kidneys, liver, brain and cardiovascular system can all be affected. The result is fundamentally different from simply feeling tired because of hot weather.

If the body has its own system for removing heat, prevention begins before that system is forced to operate at its limits.

The basic idea is not simply to “escape the heat,” but to reduce the thermal load placed on the body and help it lose heat more effectively.

The World Health Organization recommends avoiding outdoor activity and strenuous exercise during the hottest part of the day, staying in the shade or cool places, keeping homes cool, wearing light and loose-fitting clothing, using cool showers or other methods to cool the body, and maintaining hydration. WHO also emphasizes paying attention to people who are more vulnerable to heat. (6)

These measures may seem simple, but they target the same mechanisms described by heat physiology. Reducing exposure to heat reduces the amount of heat the body has to remove. Staying in a cooler environment can reduce thermal load, while cooling the skin can support heat loss. Maintaining hydration helps the body cope with fluid losses associated with sweating.

But heat protection is not only an individual responsibility. WHO’s 2026 guidance on heat-health action plans emphasizes coordinated public-health measures, including governance, heat-health warning systems, identifying populations at increased risk, communication, health-system resilience, reducing heat exposure, surveillance, and monitoring and evaluation. (7)

In other words, responding to heat has two interconnected levels: A body trying to maintain its internal temperature — and a society trying to reduce the risk from the outside.

Prevention is not only about knowing how to cool the body. It also means recognizing when symptoms require serious attention.

Heat-related illness can involve headache, dizziness, weakness, nausea, heavy sweating and muscle cramps. (6, 8)

Confusion, delirium, seizures or loss of consciousness — particularly in the context of severe heat exposure — are warning signs requiring urgent medical attention. Heatstroke is a medical emergency. (6, 8)

This brings us back to the beginning of the story. The body can provide warning signals before the most dangerous stages of heat illness, but their significance depends on the context of heat exposure and on recognizing when the body’s ability to compensate may be failing.

Two people can be exposed to the same weather conditions while experiencing very different effects. The reason is that the body’s ability to cope with heat is not identical in everyone.

Age, health status, physical activity, duration of exposure, environmental conditions and heat acclimatization can all influence the level of heat strain experienced by the body. (1, 6)

WHO identifies outdoor and manual workers, athletes and other groups as being particularly exposed to heat because of their activities or working conditions. (6)

The CDC also identifies several groups that may face greater risks, including older adults, young children, pregnant people, people with certain chronic conditions, and people who work or exercise outdoors in the heat. (8)

So the question “How hot is it?” matters. But it is not the only question.

According to Dr. Firas Awawdeh, an emergency and general physician, the body’s ability to tolerate high temperatures differs from one person to another and is influenced by physiological condition and hydration status.

Awawdeh says heat-related symptoms are repeatedly seen among people who work outdoors or remain exposed to direct sunlight for prolonged periods.

He emphasizes hydration as an important part of prevention during periods of high temperatures, particularly through adequate fluid intake, with water as a key source.

If symptoms associated with heat stress appear, he advises moving the person to a shaded or cooler place, removing unnecessary clothing or accessories that may interfere with cooling, and seeking medical care when symptoms are severe or worsening.

According to data from his own clinic, Awawdeh says the number of heat-related cases he treated in 2026 was lower than in 2025, which he attributes, among other factors, to differences in temperatures he observed during the two years.

These figures are specific to his clinic and do not represent national statistics on heat-related illness in Palestine.

If we follow the entire journey, the picture looks very different from simply having “a hot day.”

The story begins with an increase in thermal load. The body responds by trying to lose heat through increased skin blood flow and sweating. The cardiovascular system then becomes part of the cooling process, while sweating causes water and electrolyte loss. The kidneys help regulate fluid and electrolyte balance and respond to changes in circulation. Under heat stress, especially when dehydration and physical activity are also present, the risk of kidney injury can increase. (2, 3)

If thermal load continues and heat loss becomes insufficient, internal body temperature begins to rise. In severe cases, the central nervous system may become affected, while inflammation, oxidative stress, vascular injury and coagulation disturbances can contribute to systemic injury involving multiple organs. (4, 5)

This is not a sequence of isolated events. It is a connected system. One response leads to another as the body tries to preserve its balance — until the thermal load becomes greater than the body’s ability to compensate.

Do you think of the body as simply a structure that feels heat? If we stop for a moment and consider what happens inside, we find a remarkably complex system working continuously:

• The nervous system coordinates the response.
• Skin blood vessels change blood flow.
• Sweat glands help remove heat.
• The heart adapts to changes in circulation.
• The kidneys help regulate water and electrolytes.

When the amount of heat gained becomes greater than the amount of heat the body has to lose, its protective mechanisms do not simply switch off. They continue working while the physiological burden increases across several systems.

If the thermal load exceeds the body’s ability to compensate, impaired thermoregulation can progress to severe heat injury affecting the nervous system and other organs. (1, 4, 5)

And here lies the paradox: Heat begins outside the body, but its most dangerous events may unfold within. The drop of sweat we see on the skin is not the whole story. It is a visible sign of an entire system working behind it. And danger does not begin simply when the weather becomes “too hot”, but when the thermal load exceeds the body’s capacity to dissipate heat and preserve its balance.

References & Sources

[1] Cramer, M. N., Gagnon, D., Laitano, O., & Crandall, C. G. (2022). Human temperature regulation under heat stress in health, disease, and injury. Physiological Reviews, 102(4), 1907–1989. DOI: 10.1152/physrev.00047.2021.

[2] Crandall, C. G., & Wilson, T. E. (2015). Human cardiovascular responses to passive heat stress. Comprehensive Physiology, 5(1), 17–43. DOI: 10.1002/cphy.c140015.

[3] Chapman, C. L., Johnson, B. D., Parker, M. D., Hostler, D., Pryor, R. R., & Schlader, Z. (2021). Kidney physiology and pathophysiology during heat stress and the modification by exercise, dehydration, heat acclimation and aging. Temperature, 8(2), 108–159. DOI: 10.1080/23328940.2020.1826841.

[4] Yoneda, K., Hosomi, S., Ito, H., et al. (2024). How can heatstroke damage the brain? A mini review. Frontiers in Neuroscience, 18, 1437216. DOI: 10.3389/fnins.2024.1437216.

[5] Alawad, A., Merghani, T., Yousif, N., et al. (2025). Heat stroke dysfunctions: from pathophysiology to prediction. Frontiers in Physiology, 16, 1700342. DOI: 10.3389/fphys.2025.1700342.

[6] World Health Organization. (2026). Heat and health. Updated 31 July 2026.

[7] World Health Organization Regional Office for Europe. (2026). Heat–health action plans: guidance, second edition. 11 June 2026.

[8] Centers for Disease Control and Prevention. (2026). About Heat and Your Health. Updated 20 July 2026.

Local and first-hand sources

Dr. Firas Awawdeh — Emergency and general physician; interview and clinic-specific observations cited in the report.

Majdi Khalil — Construction worker from Nablus; first-hand account of symptoms experienced during work in hot conditions.