Global temperatures have been rising, and with it, more hot days and intense heatwaves.
The frequency of heat-related illness is rising, even in temperate climates.
Heat-related illness can be a medical emergency and can result in deaths in as high as 70% of heat stroke cases.
However, if treated appropriately in a timely manner, survival rates can approach about 100%.
The human body maintains its temperature within a narrow range of 36°C to 38°C.
However, sometimes, the body’s thermoregulatory responses are inadequate.
This can be due to:
- The body’s physiological limitations in responding to heat, e.g. chronic volume depletion, extremes of age and chronic illnesses
- Extrinsic factors that render heat dissipation less efficient, e.g. extreme temperatures, physical effort and environmental conditions, and
- Medication use.
When the body’s thermoregulatory responses are overwhelmed, there is protein denaturation, impaired cellular function, and later, cell death.
Damaged cells release cytokines and damage the endothelium of the blood vessels, increasing their permeability and activating the coagulation cascade.
At increased risk
Certain people are at increased risk of heat-related illness. They include:
- Babies
- Young children
- Pregnant women
- Seniors aged 65 years and above
- Those with chronic conditions, e.g. diabetes, cardiovascular and/or kidney disease
- Those who work or exercise outdoors
- Those on medications like diuretics, beta-blockers, drugs with anticholinergic properties and central nervous system stimulants
- Those who are socially isolated, and
- Those who have limited access to measures to keep cool, e.g. the homeless.
Extreme heat can lead to the triggering or deterioration of certain conditions like heart attack, stroke, kidney problems, asthma and other respiratory illnesses (especially in the presence of air pollution or smoke).
Spectrum of illness
There is a spectrum of heat-related illnesses.
They can range from the minor – e.g. dehydration, heat oedema, rash, cramps, tetany, syncope and exhaustion – to the major, i.e. heat stroke.
The features of dehydration include thirst, dry mouth, passing less urine than usual, dark or strong-smelling urine, dizziness or headache, and/or irritability or difficulty thinking clearly.
The features of heat oedema include mild swelling of the feet, ankles and hands.
It appears after a few days of exposure to a hot environment.
The features of heat rash (also termed prickly heat) include a maculopapular, erythematous rash that occurs over covered areas of body and itchiness.
It can occur at any age, but is more common in children.
Prolonged or repeated heat exposure may lead to chronic dermatitis.
The features of heat cramps include painful muscle pains or spasms, usually in the abdomen, arms or legs.
The cramps may occur after strenuous activity in a hot environment, and are more common with profuse sweating and consumption of water or hypotonic beverages.
They are usually of limited duration.
They may also be a sign of heat exhaustion.
The features of heat tetany include hyperventilation (rapid breathing), paraesthesia (“pins and needles” sensation) of the extremities, and spasms around the mouth, hands and feet.
The features of heat syncope include postural hypotension, where blood pressure drops suddenly when standing up after sitting or lying down.
It is common in senior citizens who are not used to high temperatures.
The features of heat exhaustion include heavy sweating, headache, nausea, vomiting, malaise, dizziness, muscle cramps, fainting and a rapid pulse, as well as a body temperature that is normal or less than 40°C.
It may progress to heat stroke if treated inadequately or there is failure to respond to treatment.
Medical emergency
Heat stroke is defined as a core temperature more than 40.5°C, accompanied by central nervous system dysfunction.
There are two presentations of heat stroke: classical and exertional.
Classical heat stroke occurs slowly, from a few hours to days, during which volume and electrolyte loss occurs.
The risks are increased in senior citizens, the young, and those with impairments of heat loss mechanisms due to their physical or mental health, or drugs.
It commonly occurs during severe heat waves (i.e. environmental temperature of more than 39.2°C).
Exertional heat stroke occurs in the healthy young who exert themselves beyond their body’s capacity.
It occurs over hours in normal, humid or hot environments, and is common in Malaysia.
The features of heat stroke include:
- Profuse sweating
- Core body temperature of more than 40°C
- Rapid pulse
- Rapid breathing
- Signs of central nervous system dysfunction, e.g. confusion, delirium, ataxia (lack of muscle coordination and control), seizures and coma, and
- Other features that occur in the advanced stage, e.g. anhidrosis (inability to sweat normally), coagulopathy (blood cannot clot properly) and multi-organ failure.
Heat stroke is a medical emergency.
There is no specific diagnostic test.
The tests that are usually done are for the detection of organ damage and ruling out other causes of a body temperature that is more than 40°C and central nervous system dysfunction.
Management involves measures to cool the body down, admission to the hospital, and treating the symptoms and side effects that can lead to irreversible injury and death.
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Keep it cool
Heat-related illnesses can be prevented.
The measures include keeping cool, staying hydrated, planning ahead, and checking in with family, friends and colleagues, especially in extreme heat.
Keeping cool involves:
- Wearing light and loose-fitting clothes
- Keeping the skin moist or wet with cool showers and/or the use of damp sponges or sprays
- Using blinds or curtains to prevent the sun shining directly through windows
- Using fan(s) or air conditioning, and
- Opening doors and/or windows if it is hotter indoors than outdoors.
Stay hydrated by regularly drinking fluids before one feels thirsty, especially if one is outdoors or performing physical activity; and watch for features of dehydration.
If one has been advised to limit fluid intake for medical reasons, then ask the doctor how much to drink during hot weather.
Planning ahead involves:
- Rescheduling or cancelling non-essential activities;
- Planning essential activities for the coolest part of the day
- Avoiding exercise and being outdoors when it is hot
- Ensuring that medicines and foods are stored at appropriate temperatures
- Checking with the doctor if changes are needed with medicines in extreme heat
- Ensuring the fan(s) and air-conditioning are working well, including regular servicing, and
- Taking measures to ensure the home is kept cool, e.g. installing curtains or blinds, and planting trees and plants to provide shade.
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Checking in with family, friends and colleagues, especially those at increased risk of heat-related illness or who may need assistance during times of extreme heat, could help prevent heat-related incidences.
Monitoring of the weather forecast and acting on the information provided is advisable.
It is important to remember the adage “Prevention is better than cure”.
ALSO READ: Drink more water! 5 tips to help beat the heat from a TCM perspective
Dr Milton Lum is a past president of the Federation of Private Medical Practitioners Associations and the Malaysian Medical Association. For more information, email starhealth@thestar.com.my. The views expressed do not represent that of organisations that the writer is associated with. The information provided is for educational and communication purposes only, and it should not be construed as personal medical advice. Information published in this article is not intended to replace, supplant or augment a consultation with a health professional regarding the reader’s own medical care. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.
Editor's note: This column was originally published online on July 22, 2025.
