4 Aug 2023

Two Warning Signs Displayed on Skin, Differentiating Between Heat Exhaustion and Heatstroke

– The information has been reviewed by Dr. Ko Hiu Fai

Exercising outdoors in the summer heat may put us at risk of heat exhaustion or heatstroke, both categorized as heat-related illnesses. Heatstroke is considered a life-threatening condition as it involves an excessive rise in body temperature. By observing a person’s skin temperature and condition, we can preliminarily determine whether the person is suffering from heat exhaustion or heatstroke, and make an appropriate decision regarding emergency treatment to reduce the risk of serious complications or death.


Skin and core body temperatures are key to differentiating between heat exhaustion and heatstroke. Patients suffering from heat exhaustion generally have cool, moist skin and a body temperature not higher than 40°C, while those suffering from heatstroke will have flushed skin, display feverish symptoms, and have a body temperature of over 40°C.


These differences in symptoms are related to the cause of illness. Under hot, humid conditions, patients with heat exhaustion will sweat heavily, causing their blood pressure to lower and heart rate to increase. This may lead to dizziness, fainting, muscle cramps, and dehydration, and as a result, the patient will have cool, moist skin but still remain lucid.

Cool, Moist Skin – A Sign of Heat Exhaustion
Cool, Moist Skin – A Sign of Heat Exhaustion

In contrast to those suffering from heat exhaustion, patients with heatstroke suffer from a compromised sweating mechanism. This is because on hot, humid days, a person’s sweat may become difficult to evaporate. When evaporation of sweat is slowed, heat accumulates within the body and body temperature rises, often exceeding 40°C. The skin may grow red and hot, and the patient may become confused or distressed.


If patients with heatstroke do not bring down their body temperature and receive emergency treatment, they may be at risk of death. The risk of death from heatstroke is higher than that of heat exhaustion, though heat exhaustion should not be taken lightly. If you feel dizzy, unstable, extremely thirsty, or experience muscle cramps while exercising outdoors, it may be a sign of heat exhaustion. Seek a shaded place to rest and replenish your fluids and electrolytes to prevent the condition from worsening.


Heat exhaustion and heatstroke share some similar symptoms. However, if a person’s skin becomes hot and he/she displays an altered mental state or behavior, the person may already be suffering from heatstroke. It is important to immediately cool the person down by bringing him/her to a shaded place away from the sun. Wiping the person’s body with wet towels and removing clothing are also helpful ways to bring down body temperature.

Heatstroke May Cause Organ Damage
Heatstroke May Cause Organ Damage

When patients suffering from heat exhaustion or heatstroke are sent to the hospital for emergency treatment, the medical team will generally take their body temperature and assess their mental state. If they are diagnosed with heat exhaustion, patients will be given IV therapy to replenish their fluids, and are usually discharged from the hospital relatively quickly.


Heatstroke is a more serious condition as it can lead to multiple organ failure. When the body temperature reaches 41°C or 42°C, vital organs such as the brain may become damaged, the mental state may be impaired, the risk of heart attack increases, and liver, kidney, and blood clotting functions may also be affected.


Initial treatment for heatstroke involves bringing the body temperature down to 38°C as quickly as possible, with patients generally sent to the intensive care unit for further treatment. Ice packs may be placed on the patient’s forehead, armpits, or groin, and a rectal thermometer may be used to regularly monitor the patient’s body temperature to avoid sudden, dramatic changes in temperature.

Prevent Heat-Related Illnesses by Drinking More Water
Prevent Heat-Related Illnesses by Drinking More Water

To prevent heat exhaustion and heatstroke, stop exercising if you feel unwell. Drinking enough water prior to exercising will also help prevent excessive perspiration, which can lead to heat exhaustion. Furthermore, avoid drinking beer while exercising as alcoholic drinks dilate the blood vessels and may increase blood flow, accelerating the onset of heat exhaustion.


There are many ways to treat heat exhaustion and heatstroke, each with different results and side effects. Patients with questions should consult their doctor.