Heat- Related Illnesses are the various manifestations of extreme heat and are increasing with increased global warming and heat waves. Periods of extreme heat that have an effect on human health are referred as heat waves. Climate change is leading to an increase in average temperatures and increased possibilities of severe heat waves. The impact of extreme summer heat on human health may be exacerbated by increase in humidity. Heat waves are an emerging public-health problem.

Extreme heat can lead to minor illnesses, such as heat rash (prickly heat), heat oedema, heat cramps, and tetany, as well as serious illnesses as heat syncope, heat exhaustion and heat stroke. Heat stroke is the most severe form of the heat-related illness. The mortality rate among heat stroke victims is as high as one-third, and one-fifth of the heat stroke survivors suffer neurologic damage.

Heat-related illnesses include:

  • Heat rash (Prickly heat): small, red, papules develop in hot climate when the sweat ducts to the skin become blocked or swell, causing discomfort and itching.
  • Heat cramps occur in muscles after exercise in hot climate because sweating causes the body to lose water, salt, and minerals (electrolytes).
  • Heat oedema (swelling) in the legs and hands, can occur after sitting or standing for a long time in a hot environment.
  • Heat tetany is usually caused by short periods of stress in a hot environment.
  • Heat syncope (fainting) occurs from low blood pressure. Heat causes the blood vessels to expand (dilate) and body fluids move into the legs because of gravity.
  • Heat exhaustion (heat prostration) generally develops when a person is working or exercising in hot weather and does not drink enough liquids to replace those lost liquids.
  • Heat stroke (sun stroke) is a severe heat illness defined as hyperthermia with a body temperature greater than 40 °C (104 °F) with neurologic dysfunction because of environmental heat exposure with lack of thermoregulation (process by which the body maintains a steady temperature). It is also known as sun stroke.

Heat stroke is a medical emergency. Even with immediate treatment, it can be life-threatening or cause serious long-term problems.

Heat- related illness is a common problem in the tropics and with ever-increasing global warming its incidence is rising even in temperate climate. The highest incidence of heat illness of 45-1300/100000 persons is reported from Saudi Arabia.

Children, elderly persons, chronically ill persons, outdoor workers, pavement and slum dwellers, street venders and rickshaw pullers are at greater risk of heat related illnesses.

Greater awareness about heat related illnesses will help in preventing, recognizing and treating these disorders at an early stage. Public education on heat illnesses, behavioural changes and restricted use of alcohol, enforced rests and fluid protocols, acclimatisation and ready availability of cooling facilities in hot areas will help in decreasing morbidity and mortality. Most heat-related illnesses can be prevented by keeping the body cool and by avoiding dehydration in hot environments.


Symptoms of various heat related illnesses are-

  • Heat rash (Prickly heat) – Small, red, itchy papules appear on the face, neck, upper chest, under breast, groin and scrotum areas. This can affect any age but is prevalent in young children. Infection with Staphylococcus can occur.
  • Heat cramps-Muscle cramping might be the early sign of heat-related illness, and may lead to heat exhaustion or stroke. Symptoms of heat cramps include profuse sweating with involuntary spasms of the large muscles in the body.
  • Heat oedema is swelling of legs and hands. Older adults have an increased risk of heat oedema, especially if they have other medical conditions that affect their circulation. People visiting hot climates from colder climates may also have an increased risk of heat oedema.
  • Heat tetany- Symptoms may include hyperventilation, respiratory problems, numbness or tingling, or muscle spasms.
  • Heat syncope (fainting) – Symptoms of heat syncope include light-headedness, dizziness, fainting. Heat causes the blood vessels to expand (dilate), so body fluid moves into the legs by gravity and causes low blood pressure and may result in fainting.
  • Heat Exhaustion: symptoms are fatigue, weakness, dizziness, headache, nausea, vomiting, muscle cramps and sweating; skin is pale, cool, and moist.
  • Heat stroke results in high body temperature 40 °C (104 °F) or more, hot, red, dry skin, rapid and week pulse (tachycardia), tachypnoea (rapid breathing), nausea, hypotension, unconsciousness (delirium, seizures, stupor, confusion or coma).


As the body temperature increases, the body tries to maintain its normal temperature by transferring heat. Sweating and blood flow to the skin (Thermoregulation) help to keep body cool. A heat-related illness occurs when the body cannot transfer enough heat to keep the body cool. A high body temperature (hyperthermia) can develop rapidly in extremely hot environments.

Heat-related illnesses produce a high body temperature because the body cannot transfer heat effectively or because external heat gain is excessive.(High temperature caused by a fever is different from a high body temperature caused by a heat-related illness. A fever is the body’s normal reaction to infection and other conditions).

Heat rash (Prickly heat) develops when the sweat ducts become blocked and swell. It is attributed to heavy sweating during hot and humid weather.

Heat oedema develops when heat causes the blood vessels to expand (dilate) and body fluid moves into the hands or legs by gravity. If salt loss is less than normal, the increased salt level draws fluid into the hands and legs. Older adults have an increased risk of heat oedema, especially if they have other medical conditions that affect their circulation. People visiting hot climates from colder climates may also have an increased risk of heat oedema.

Heat syncope occurs when heat causes the blood vessels to expand (dilate) in order to keep body cool; as a result blood flow to the brain is reduced causing fainting. Heat Syncope can also be caused as a result of blood collecting in the legs if an individual is standing for an extended period of time in the hot sun or as a result of doing rigorous physical activity for an extended amount of time out in the sun.

Heat exhaustion occurs when body loses body fluids and salts (sweating), when exposed to high temperatures for long periods of time.  It can develop when person works or exercises in hot weather and doesn’t drink enough liquids to replace the fluids lost from sweating.

Heat stroke results when the body fails to regulate its own temperature, and body temperature continues to rise. Heat stroke is the most serious heat-related disorder. It occurs when the body fails to regulate its own temperature, the body’s temperature rises rapidly, the sweating mechanism fails, and the body is unable to cool down. The body temperature can rise to 106 degrees Fahrenheit (41.1 degree Celsius) or higher within 10 to 15 minutes. Heat stroke can cause death or permanent disability if prompt medical treatment is not given.

There are two forms of heat stroke:

  • Exertional heat stroke (EHS) generally occurs in young individuals who engage in strenuous physical activity for a prolonged period of time in a hot environment.
  • Classic non-exertional heat stroke (NEHS) more commonly affects sedentary elderly individuals, persons who are chronically ill and very young children during environmental heat waves. Classic NEHS is more common in areas that do not experience periods of prolonged hot weather.

Risk factors for heatstroke include male sex, sleep deprivation, obesity, poor physical conditioning, lack of acclimatization, diuretic therapy, dehydration, febrile illness, alcohol abuse, skin diseases that affect sweating, heavy protective gear, drugs impairing normal thermoregulatory response, and a past history of HS.


In most cases diagnosis is made clinically. This involves taking the temperature and assessing the symptoms of heat exhaustion and heat stroke.

Baseline tests should include:

Blood test for:

  • Complete blood cell count- Elevated white blood cell counts are observed in patients with heatstroke and Platelet levels may be low.
  • Arterial blood gas testing and lactic acid analysis may reveal respiratory alkalosis due to direct central nervous system (CNS) stimulation and metabolic acidosis due to lactic acidosis.
  • Glucose- Hypoglycemia may occur in patients with EHS and in patients with fulminate hepatic failure.
  • Electrolytes estimation-
    • Sodium- Hypernatremia (increased sodium levels) may be found due to reduced fluid intake and dehydration early in the course of disease or due to diabetes insipidus.  Hyponatremia (decreased sodium levels) is observed due to excessive sodium losses in sweat, patients using hypotonic solutions, such as water, and in patients using diuretics.
    • Potassium– Hykalemia is common in the early phase of heatstroke and with increasing muscle damage, hyperkalemia may be found.
  • Liver function test- Aspartate aminotransferase (AST) and Alanine aminotransferase (ALT) levels may rise in heat stroke.
  • Kidney function test- Raised serum uric acid levels, blood urea nitrogen, and serum creatinine are common in patients whose are complicated by renal failure.
  • Urine test for presence of myoglobin in urine.

Muscle function test- Creatinine kinase (CK), lactate dehydrogenase (LDH), aldolase, and myoglobin are released from muscles when muscle necrosis occurs.

Cerebrospinal fluid analysis- Cerebrospinal fluid (CSF) cell counts may show a nonspecific pleocytosis and CSF protein levels may be elevated.

Imaging Studies-

  • Computerized tomography scans may be helpful in ruling out central nervous system (CNS) injury in patients with altered mental status.
  • Chest radiographs may show atelectasis, pneumonia, pulmonary infarction, or pulmonary edema.

Other Tests-

  • Electrocardiography: Sinus tachycardia of 130-140 beats per minute and nonspecific and ischemic ST-T wave abnormalities are common.


Heat rash

  • Rash subsides with no specific treatment.
  • Minimize sweating by staying in an air-conditioned environment, taking frequent showers and wearing light clothes.
  • Keep the affected area dry. Topical antihistamine and antiseptic preparations can be used to reduce discomfort and prevent itching.

Heat cramps-Treatment of heat cramps include rest, cooling the body, oral hydration, and stretching the muscles that are cramping. Medical attention should be sought if heat cramps are sustained for more than one hour.

Heat oedema– Treatment is not required as oedema usually subsides following acclimatization. Diuretics are not advised and avoid the heat as much as possible.

Heat syncope-The patient should rest in a cool place and be placed in a supine position with legs and hips elevated to increase venous return. Other serious causes of syncope need to be ruled out.

Heat exhaustion:

  • Move the patient to a cool, shaded room or air-conditioned place.
  • The patient should be undressed.
  • Apply cold wet sheet or spray cold water and use fan if available.
  • Lay the patient down and raise his or her legs and hips to increase venous return.
  • Start oral hydration. If nausea prevents oral intake of fluids, consider intravenous hydration.
  • If hyperthermia is above 39°C or impaired mental status or sustained hypotension occurs, treat as heatstroke and transfer the patient to hospital.

Heat stroke

  • Measure core temperature (rectal probe): if > 40°C, move to a cooler place,
  • remove clothing,
  • Initiate external cooling: cold packs on the neck, axillae and groin, continuous fanning (or keep ambulance windows open) while skin is sprayed with water at 25–30°C,
  • position an unconscious patient on his or her side,
  • clear airway to minimize risk of aspiration,
  • administer oxygen 4 l/min and isotonic crystalloid (normal saline) solution,
  • transfer rapidly to the medical emergency department.


Long term measures: to reduce urban heat island effects:

  • Planting trees and vegetations: lowers surface and air temperatures by providing shade and cooling through evapotranspiration.
  • Install green roofs or rooftop garden: It is a vegetative layer grown on a rooftop. Green roofs provide shade and remove heat from the air through evapotranspiration, reducing temperatures of the roof surface and the surrounding air.
  • Install cool roofs or reflective roofs: help to reflect sunlight and heat away from home, reducing roof temperatures.
  • Use energy-efficient appliances and equipments

To minimise the impact during the heat wave and to prevent serious heat related illnesses at community and individual level following DO’s and DONT’s are suggested:


 Listen to Radio, watch TV, read News paper for local weather forecast to know if a heatwave is on the way.

Regularly drink water or other nonalcoholic fluids (homemade drinks like lassi, torani (rice water), lemon water, buttermilk, panna) and as often as possible, even if not thirsty.

  • Eat light, cool, easy-to-digest foods such as fresh fruits or salads (thoroughly clean with safe water).
  • Wear loose fitting, lightweight, light-coloured, and porous cotton clothes.
  • Use protective goggles, umbrella/hat, shoes or chappals while going out in sun.
  • While travelling, carry water with you.
  • If you work outside, use a hat or an umbrella and also use a damp cloth on your head, neck, face and limbs.
  • Check on children, older, sick, or frail people, friends, family, and neighbors who may need your help in responding to the heat.
  • Know the symptoms of excessive heat exposure and the appropriate responses. If you feel faint or ill, see a doctor immediately.
  • Keep animals in shade and give them plenty of water to drink.
  • Keep your home cool, use curtains, shutters or sunshade and open windows at night. Reflective material such as tin foil or aluminium foil can be used as window reflectors. (Wrap it around some cardboard and put the reflectors between the glass and the window coverings).
  • Use fans (place the fan at a certain distance from people, when the temperature is at higher levels hot air can cause excess dehydration).
  • Take a cool bath.
  • Provide cool drinking water near work place.
  • Caution workers to avoid direct sunlight.
  • Schedule strenuous jobs to cooler times of the day.
  • Increase the frequency and length of rest breaks for outdoor activities.
  • Pregnant workers and workers with a medical condition should be given additional attention.


  • Don’t leave children and pets alone in parked cars for any amount of time.
  • Avoid going out in the sun, especially between 12.00 noon and 3.00 p.m.
  • Avoid wearing dark, heavy or tight fitting clothes.
  • Don’t drink alcohol to stay cool, avoid excessive use of tea, coffee and liquids containing high amounts of sugar.
  •  Avoid heavy, hard-to-digest foods and do not eat stale food.
  • Avoid strenuous activities when the outside temperature is high.
  •  Avoid working outside between 12 noon and 3 p.m.
  •  Avoid cooking during peak hours. Open doors and windows to ventilate cooking area adequately.


People who have come from a cooler climate to a hot climate during the heat wave season are at risk for heat related illness. They should not move in open area for a period of one week till the body is acclimatized to heat and should drink plenty of water. Acclimatization is achieved by gradual exposure to the hot environment during heat wave.

Emergency kit –

  • Water bottle
  • Umbrella/ Hat or Cap / Head Cover
  • Hand Towel
  • Hand Fan
  • Electrolyte / Glucose / Oral Rehydration salts (ORS)

If someone is suffering from the heat related illness:

  • Move the person to a cool place under the shade.
  • Give water or a rehydrating drink (if the person is still conscious).
  • Fan the person.
  • Do not give alcohol, caffeine or aerated drink.
  • Cool the person by putting a cool wet cloth on his/her face/body.
  • Loose clothes for better ventilation.
  • Consult a doctor if symptoms get worse or are long lasting or the person is unconscious.

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