The presentations common with heat exhaustion may develop suddenly or over a period of time especially after extended periods of exercise [7]. Possible symptoms and signs of heat exhaustion include the following:

• Cool, moist skin with goose bumps when under hot temperature
• Heavy sweating
• Faintness
• Dizziness
• Fatigue
• Weak, rapid pulse
• Low blood pressure upon standing
• Muscle cramps
• Nausea
• Headache

• Weakness

  Signs and Symptoms Of heat exhaustion: increased thirst weakness and extreme tiredness fainting muscle cramps nausea and vomiting irritability headache increased sweating cool, clammy skin body temperature rises, but to less than 105°F (40.5°C) Of heatstroke [kidshealth.org]

  Signs of heat exhaustion include cool, moist, pale, ashen or flushed skin, as well as: headache nausea dizziness weakness exhaustion. [sharecare.com]

  Weakness. Feeling dizzy. Headache. Nausea. Vomiting can occur. Muscle cramps. Weak or rapid pulse. Causes Anything that keeps the body's natural cooling system from working right can lead to heat exhaustion and heat stroke. [healthy.net]

  Heat exhaustion is a non–life-threatening clinical syndrome of weakness, malaise, nausea, syncope, and other nonspecific symptoms caused by heat exposure. [msdmanuals.com]

• Fatigue

  Johnson, Ars Technica, "It’s too soon to tell if the Great Barrier Reef’s bleaching was a catastrophe," 27 July 2018 Signs of heat exhaustion include fatigue, heavy sweating, dizziness, fainting, thirst, headache, and more. — Nina Bahadur, SELF, "Why [merriam-webster.com]

  "Parents are informing me that they're children feel fatigued. They're pale. They're vomiting. That's serious," Pimentel said. She bought fans for her classroom. But they circulate hot air. [hawaiinewsnow.com]

  Other signs and symptoms might include confusion or dizziness, decreased urination, nausea and vomiting, headache, fatigue/weakness and malaise. This answer provided for NATA by the Marist College Athletic Training Education Program. [sharecare.com]

  The real problem is that of heat and humidity which produces heat exhaustion and fatigue, and irritability which comes from long hours spent running wet with sweat. [dictionary.cambridge.org]

  Symptoms of heat exhaustion include heavy sweating, extreme weakness or fatigue, dizziness/confusion, nausea, clammy/moist skin, pale or flushed complexion, muscle cramps, slightly elevated body temperature and fast/shallow breathing. [orange.floridahealth.gov]

• Fever

  Brugada syndrome (BrS) as an established channelopathy can be unmasked by various triggers like drugs, fever, etc. [ncbi.nlm.nih.gov]

  The person has a fever over 102°F (38.9°C). Other symptoms of heatstroke are present (like rapid pulse or rapid breathing). The person's condition does not improve, or worsens despite treatment. [mountsinai.org]

  Fever. Anyone with a current or recent fever may be at increased risk. Medications. Diuretics and stimulants may increase risk. Sickle cell trait. Sickle cell trait or disease increases the risk for heat illness. [orthoinfo.aaos.org]

  S igns and symptoms resemble those of shock and may include: Feeling faint Nausea Heavy sweating Ashen appearance Rapid, weak heartbeat Low blood pressure Cool, moist skin Low-grade fever Abdominal cramps If you suspect heat exhaustion: Get the person [tripleonecare.co.nz]

• Hyperthermia

  Despite initial presentations with severe hyperthermia, tachycardia and hypotension, only one patient with heat stroke had myocardial ischemia. The CPK isoenzymes were not indicative of myocardial damage in any patient. [ncbi.nlm.nih.gov]

  The diagnosis of heatstroke rests on two critical factors: hyperthermia and central nervous system dysfunction. [aafp.org]

  Read more on Better Health Channel website Heat stress - NT.GOV.AU Avoiding heat stress, people at risk, minor conditions, heat exhaustion and heat stroke or hyperthermia. [healthdirect.gov.au]

  For overheating of the body, see Hyperthermia. "Calenture" redirects here. For the album by The Triffids, see Calenture (album). Heat illness is a spectrum of disorders due to environmental exposure to heat. [en.wikipedia.org]

• Malaise

  Heat exhaustion is a non–life-threatening clinical syndrome of weakness, malaise, nausea, syncope, and other nonspecific symptoms caused by heat exposure. [msdmanuals.com]

  Heat exhaustion is characterized by nonspecific symptoms such as malaise, headache, and nausea. Treatment involves monitoring the patient in a cool, shady environment and ensuring adequate hydration. [ncbi.nlm.nih.gov]

  Other signs and symptoms might include confusion or dizziness, decreased urination, nausea and vomiting, headache, fatigue/weakness and malaise. This answer provided for NATA by the Marist College Athletic Training Education Program. [sharecare.com]

• Tachypnea

  Tachycardia and tachypnea are present. Complications of heat exhaustion include impending heatstroke and shock. Management - Remove the patient from the hot environment. [chemm.nlm.nih.gov]

  Tachycardia, tachypnea, and normotension are common in heatstroke. Temperature also should be measured in the initial survey. [aafp.org]

• Nausea

  Heat exhaustion is a non–life-threatening clinical syndrome of weakness, malaise, nausea, syncope, and other nonspecific symptoms caused by heat exposure. [msdmanuals.com]

  […] of heat exhaustion include nausea vomiting, lethargy, increased heart rate, increase temperature. [sharecare.com]

  Symptoms: Nausea Extreme fatigue Reduced sweating Headache Shortness of breath Weak, rapid pulse Dry mouth Rectal temperature less than 104?F. [momsteam.com]

  Heat exhaustion is characterized by nonspecific symptoms such as malaise, headache, and nausea. Treatment involves monitoring the patient in a cool, shady environment and ensuring adequate hydration. [ncbi.nlm.nih.gov]

• Vomiting

  If the child is vomiting, turn onto his or her side to prevent choking. Think Prevention! Teach kids to always drink plenty of liquids before and during any activity in hot, sunny weather — even if they aren't thirsty. [kidshealth.org]

  […] of heat exhaustion include nausea vomiting, lethargy, increased heart rate, increase temperature. [sharecare.com]

  […] if they are too confused to drink and/or are vomiting If untreated, heat exhaustion may progress to heat stroke. [en.wikipedia.org]

  If vomiting or nausea prevents oral rehydration, IV fluid and electrolyte replacement therapy, typically using 0.9% saline solution, is indicated. [msdmanuals.com]

• Loss of Appetite

  Loss of appetite and feeling sick 4. Sweating with pale clammy skin 5. Cramps in the arms, legs and stomach 6. [sja.org.uk]

  Check for signs of heat exhaustion The signs of heat exhaustion include: headache dizziness and confusion loss of appetite and feeling sick excessive sweating and pale, clammy skin cramps in the arms, legs and stomach fast breathing or pulse temperature [nhs.uk]

  The symptoms of heat exhaustion include: headache, dizziness and confusion, loss of appetite and feeling sick, excessive sweating and pale clammy skin, cramps in the arms, legs and stomach, fast breathing or fast pulse, temperature of 37C or above, intense [metro.co.uk]

• Hypotension

  Despite initial presentations with severe hyperthermia, tachycardia and hypotension, only one patient with heat stroke had myocardial ischemia. The CPK isoenzymes were not indicative of myocardial damage in any patient. [ncbi.nlm.nih.gov]

  On examination, patients appear tired, are usually sweaty and tachycardic, and may have orthostatic hypotension. Mental status is intact, unlike in heatstroke. Temperature is usually normal and, when elevated, usually does not exceed 40° C. [msdmanuals.com]

  On examination, patients appear tired, are usually sweaty and tachycardic, and may have orthostatic hypotension. Mental status is intact, unlike in heatstroke. Temperature is usually normal and, when elevated, usually does not exceed 40 ° C. [merckmanuals.com]

  […] heat exhaustion include – Hot and flushed skin that appears as a fever Heavy and profuse sweating Intense thirst Dizziness and fatigue Nausea and vomiting Confusion Headaches Black outs or syncope and sudden fall of blood pressure called orthostatic hypotension [news-medical.net]

• Orthostatic Hypotension

  On examination, patients appear tired, are usually sweaty and tachycardic, and may have orthostatic hypotension. Mental status is intact, unlike in heatstroke. Temperature is usually normal and, when elevated, usually does not exceed 40° C. [msdmanuals.com]

  On examination, patients appear tired, are usually sweaty and tachycardic, and may have orthostatic hypotension. Mental status is intact, unlike in heatstroke. Temperature is usually normal and, when elevated, usually does not exceed 40 ° C. [merckmanuals.com]

  As dehydration increases from the loss of body water, lightheadedness may occur and fainting ( syncope ) may occur, especially if the affected individual stands up quickly (due to orthostatic hypotension ).The person also may have a low-grade fever. [medicinenet.com]

• Tachycardia

  It demonstrates that the hemodynamic changes in severe heat exposure reflect a hyperdynamic circulation with tachycardia and high cardiac output states. [ncbi.nlm.nih.gov]

  Tachycardia and tachypnea are present. Complications of heat exhaustion include impending heatstroke and shock. Management - Remove the patient from the hot environment. [chemm.nlm.nih.gov]

  Tachycardia, tachypnea, and normotension are common in heatstroke. Temperature also should be measured in the initial survey. [aafp.org]

• Flushing

  Symptoms of heat exhaustion include heavy sweating, extreme weakness or fatigue, dizziness/confusion, nausea, clammy/moist skin, pale or flushed complexion, muscle cramps, slightly elevated body temperature and fast/shallow breathing. [orange.floridahealth.gov]

  […] increased sweating cool, clammy skin body temperature rises, but to less than 105°F (40.5°C) Of heatstroke: severe headache weakness, dizziness confusion fast breathing and heartbeat loss of consciousness (passing out) seizures little or no sweating flushed [kidshealth.org]

  Symptoms include dry, hot, and flushed skin—dark or purple in color; dilated pupils; rapid, weak pulse; shallow breathing; and high temperature that may be in excess of 106° Fahrenheit. [hunter-ed.com]

  Signs of heat exhaustion include cool, moist, pale, ashen or flushed skin, as well as: headache nausea dizziness weakness exhaustion. [sharecare.com]

• Hot, Dry Skin

  severe headache weakness, dizziness confusion fast breathing and heartbeat loss of consciousness (passing out) seizures little or no sweating flushed, hot, dry skin body temperature rises to 105°F (40.5°C) or higher What to Do If your child has symptoms [kidshealth.org]

  Heat Exhaustion Heat Stroke Dehydration Flushed, hot, dry skin with no sweating Fatigue Temperature of 105 or higher Weakness Severe, throbbing headache Clammy skin Weakness, dizziness or confusion Headache Seizure Nausea/vomiting Decreased responsiveness [active.com]

  More serious is heat stroke, where you may develop a very high body temperature (105°F or more); a rapid, strong pulse; red, hot, dry skin; a throbbing headache; dizziness; and nausea. [heartmdinstitute.com]

  Recognizing Heat Exhaustion Warning signs of heat exhaustion include: Heavy sweating Paleness Muscle cramps Tiredness Weakness Dizziness Headache Nausea or vomiting Fainting Hot dry skin Cold damp skin The skin may be cool and moist. [cchealth.org]

• Increased Sweating

  Signs and Symptoms Of heat exhaustion: increased thirst weakness and extreme tiredness fainting muscle cramps nausea and vomiting irritability headache increased sweating cool, clammy skin body temperature rises, but to less than 105°F (40.5°C) Of heatstroke [kidshealth.org]

  Acclimatization to hot environments usually occurs over 7-10 days and enables individuals to reduce the threshold at which sweating begins, increase sweat production, and increase the capacity of the sweat glands to reabsorb sweat sodium, thereby increasing [emedicine.medscape.com]

• Skin Disease

  Patients with skin diseases and those taking medications that interfere with sweating also are at increased risk for heat stroke because they are unable to dissipate heat adequately. [emedicine.medscape.com]

• Oliguria

  View/Print Table TABLE 2 Signs and Symptoms of Heat Exhaustion and Heatstroke Core Temperature* Signs Symptoms Heat Exhaustion 37°C to 40°C (98.6°F to 104°F) Anxiety Confusion Cutaneous flushing Hypotension Oliguria Pyrexia Tachycardia Vomiting Anorexia [aafp.org]

• Renal Injury

  Central nervous system injury is permanent in 20 percent of cases and is associated with poor prognosis. 23 Rhabdomyolysis caused by tissue destruction is common and results in myoglobinuria and risk of renal injury. [aafp.org]

• Dizziness

  They feel faint and dizzy. Muscle cramps in the arms, legs, or abdomen might be present. Carbo Veg : Collapse from excess heat with clamminess of the skin and stomach complaints. [homeopathycenter.org]

  Symptoms of heat stroke include extremely high body temperature above 106ºF, hot and dry skin, profuse sweating, hallucinations, chills, throbbing headache, confusion/dizziness and/or slurred speech. [orange.floridahealth.gov]

  Johnson, Ars Technica, "It’s too soon to tell if the Great Barrier Reef’s bleaching was a catastrophe," 27 July 2018 Signs of heat exhaustion include fatigue, heavy sweating, dizziness, fainting, thirst, headache, and more. — Nina Bahadur, SELF, "Why [merriam-webster.com]

  Signs of heat exhaustion include cool, moist, pale, ashen or flushed skin, as well as: headache nausea dizziness weakness exhaustion. [sharecare.com]

  […] heat exhaustion includes: Moving the person to a cool place Having the patient take off extra layers of clothes Cooling the patient down by fanning them and putting wet towels on their body Having them lie down and put their feet up if they are feeling dizzy [en.wikipedia.org]

• Confusion

  Symptoms of heat stroke include extremely high body temperature above 106ºF, hot and dry skin, profuse sweating, hallucinations, chills, throbbing headache, confusion/dizziness and/or slurred speech. [orange.floridahealth.gov]

  The earliest signs include unsteady gait and confusion. Recording of rectal temperature is essential. Skin colour, blood pressure and heart rate are not reliable diagnostic signs. The mainstays of therapy are rapid rehydration and cooling. [ncbi.nlm.nih.gov]

  You should also call 999 if the person feels hot and dry, has a temperature of 40C or above, has rapid shortness of breath, is confused, has a seizure, loses consciousness, is unresponsive. [metro.co.uk]

  Symptoms can include: Confusion Dehydration Fatigue Nausea Muscle aches Sweating Rapid heartbeat Taking a cool bath, moving to an air conditioned area and drinking hydrating fluids can often relieve heat exhaustion. [urgentcarewesthartford.com]

  […] off extra layers of clothes Cooling the patient down by fanning them and putting wet towels on their body Having them lie down and put their feet up if they are feeling dizzy Having them drink water or sports drinks – but only if they are awake, not confused [en.wikipedia.org]

• Seizure

  You should also call 999 if the person feels hot and dry, has a temperature of 40C or above, has rapid shortness of breath, is confused, has a seizure, loses consciousness, is unresponsive. [metro.co.uk]

  In addition to dizziness, confusion, and nausea, those who have heat stroke may also experience seizures, fevers, and damage to their organs. Steps to Managing Heat Exhaustion Find a cool place. [doctorshealthpress.com]

  The person goes into shock, faints, or has seizures. The person is not breathing. You also should begin CPR right away to try and revive them. [familydoctor.org]

  […] vomiting irritability headache increased sweating cool, clammy skin body temperature rises, but to less than 105°F (40.5°C) Of heatstroke: severe headache weakness, dizziness confusion fast breathing and heartbeat loss of consciousness (passing out) seizures [kidshealth.org]

• Irritability

  Signs and Symptoms Of heat exhaustion: increased thirst weakness and extreme tiredness fainting muscle cramps nausea and vomiting irritability headache increased sweating cool, clammy skin body temperature rises, but to less than 105°F (40.5°C) Of heatstroke [kidshealth.org]

  Irritability and confusion might be present. Veratrum alb : Individual might have fainted or collapsed. Face is pale with profuse and clammy sweat, extreme coldness especially to hands and feet. Pulse is rapid and weak. [homeopathycenter.org]

  […] clothing; hats; and/or helmets (for example, football pads or turnout gear) Having a higher percentage of body fat Dehydration Fever Some medications, like beta blockers and antipsychotic medicines Symptoms of heat exhaustion include nausea, dizziness, irritability [en.wikipedia.org]

  The real problem is that of heat and humidity which produces heat exhaustion and fatigue, and irritability which comes from long hours spent running wet with sweat. [dictionary.cambridge.org]

• Stupor

  Heat stroke Warm, dry skin High fever, usually over 104° F (or 40° C) Rapid heart rate Loss of appetite Nausea Vomiting Headache Fatigue Confusion Agitation Lethargy Stupor Seizures, coma, and death are possible Move to a cool place and rest. [urmc.rochester.edu]

  Heat stroke Warm, dry skin high fever, usually over 104° F (or 40° C) Rapid heart rate Loss of appetite Nausea Vomiting Headache Fatigue Confusion Agitation Lethargy Stupor Seizures, coma, and death are possible Move to a cool place and rest. [hopkinsmedicine.org]

Diagnosis is straightforward in cases of heat exhaustion as the symptoms are immediately visible to medical experts [8]. To rule out a heat stroke however, the temperature of the patient may be taking to confirm diagnosis. When heat exhaustion has already progressed to heat stroke, there are some additional tests required. These may include:

• Blood tests to confirm low blood sodium and potassium as well as the constituents of the bloods gaseous components. It can also be used to check for rhabdomyolysis. 
• Urine test to confirm the concentration and composition of your urine and also to confirm kidney function.
• Imaging tests to confirm presence or absence of damage to internal organs. 

• Hyponatremia

  Electrolyte levels should be measured to exclude severe hyponatremia in patients who have had excessive free water intake, particularly if they develop findings of brain dysfunction. [msdmanuals.com]

  Clinically significant hyponatremia often results from voluntary overhydration and can be dangerous. 20 Clinical manifestations of hyponatremia include nonspecific symptoms involving the central nervous system, such as dizziness, nausea, and malaise, [aafp.org]

Most of time, heat exhaustion can be treated without recourse to medical experts. This can be achieved by doing any of the following [9]:

• Resting in cool environments
• Intake of cold liquids
• Application of cool water to the skin
• Removal of unnecessary clothing

Within an hour of these treatment measures, the patient is supposed to feel relieved. When this is not the case, medical aid should be sought.

Common treatments used by medical experts include the use of intravenous fluids, immersion in cold water, use of ice packs and cooling blankets. 

Majority of heat exhaustion cases pass off without any major damages. An important step to recovery is the recognition of symptoms before a stroke occurs [6]. If the activity is stopped early enough, hydration will begin and the chances of complications occurring will be greatly reduced.

During and after treatment, aldosterone values were still significantly lower than normal mean (152.63 +/- 13.47, p < 0.05; 145.2 +/- 17.55, p < 0.01, respectively), thereby shedding some light on the possible etiology of persistent metabolic acidosis [ncbi.nlm.nih.gov]

Heat exhaustion and related ailments has a high incidence in the United States and there is an average of 334 deaths per year as a result of this spectrum of illnesses [4]. Internationally, heat exhaustion incidence is poorly documented as it is rarely seen in most parts of the globe especially the tropics.

Although there is a marked variation in ambient temperatures, humans as well as other mammals are able to maintain a particular body temperature by the natural ability to balance out heat gain with heat loss [5].

Heat exhaustion and other related illnesses ensue when heat gain firmly overwhelms the body’s mechanisms of heat loss. Excessive heat leads to important physiologic changes such as denaturation of proteins, destabilization of phospholipids and lipoproteins and liquefaction of membrane lipids. These lead to cardiovascular collapse, multiple organ failure and death. There is no exact temperature at which cardiovascular collapse can occur. This is because there are a variety of factors that can contribute to or delay organ dysfunction.

Heat exhaustion and heat-related illnesses can be avoided by taking any of these preventive steps when temperature is high [10]:

• Always wear loose fitting, lightweight and light coloured clothing.
• Avoid sunburn by using umbrellas and sunscreen when going out.
• Always stay in an environment cooler than the outside temperature especially when staying in a place for long.
• Consume plenty of fluids to help the body stay hydrated all the time. However, alcoholic beverages must be avoided and medical advice must be sought if already dealing with a condition that requires reduction in liquid intake. 
• Seek medical advice if you are taking any medications that make you susceptible to heat exhaustion. 
• Avoid excessively hot spots and do not drive in a hot car. Allow the car to cool off before getting in to drive. 
• If you travel to a hot environment, allow the body a few weeks to get used to the heat before getting into any strenuous activities. 

Heat exhaustion refers to one part of an ailment group known as heat-related illnesses [1]. This illness spectrum starts with heat cramps, before progression to heat exhaustion and heat stroke at the last. The natural cooling system of the body involves sweating but this can only be when there is enough fluid in the body for sweat production, circulation of air over the skin, and low air humidity which can allow sweat to evaporate.

With activities in a hot environment, the body becomes overwhelmed losing the innate ability to cool itself. This triggers heat-related symptoms.

1. Maron BJ, Doerer JJ, Haas TS, et al. Sudden deaths in young competitive athletes: analysis of 1866 deaths in the United States, 1980-2006. Circulation 2009; 119:1085.
2. Mueller FO, Cantu RC. Catastrophic sports injury research: twenty-sixth annual report. University of North Carolina, Chapel Hill 2008.
3. Rav-Acha M, Hadad E, Epstein Y, et al. Fatal exertional heat stroke: a case series. Am J Med Sci 2004; 328:84.
4. Roberts WO. Exertional heat stroke during a cool weather marathon: a case study. Med Sci Sports Exerc 2006; 38:1197.
5. Capacchione JF, Muldoon SM. The relationship between exertional heat illness, exertional rhabdomyolysis, and malignant hyperthermia. Anesth Analg 2009; 109:1065.
6. Armstrong LE, Casa DJ, Watson G. Exertional hyponatremia. Curr Sports Med Rep 2006; 5:221.
7. Bouchama A, Knochel JP. Heat stroke. N Engl J Med. Jun 20 2002;346(25):1978-88.
8. Costrini A. Emergency treatment of exertional heatstroke and comparison of whole body cooling techniques. Med Sci Sports Exerc. Feb 1990;22(1):15-8.
9. Dahmash NS, al Harthi SS, Akhtar J. Invasive evaluation of patients with heat stroke. Chest. Apr 1993;103(4):1210-4.
10. Easterling DR, Meehl GA, Parmesan C, Changnon SA, Karl TR, Mearns LO. Climate extremes: observations, modeling, and impacts. Science. Sep 22 2000;289(5487):2068-74.