Heat-related illnesses are traditionally classified according to severity as heat exhaustion, heat cramps, and heatstroke. Heat exhaustion and heat cramps are generally considered milder forms of heat-related illness.

A person who develops dizziness, headache, nausea, vomiting, weakness, a rapid heartbeat, or an elevated body temperature after exposure to a hot environment may be diagnosed with heat exhaustion. If involuntary muscle spasms occur following excessive physical activity in a hot environment, the condition is known as heat cramps.

Heatstroke is a severe and life-threatening form of heat-related illness. In addition to symptoms of heat exhaustion, heatstroke is characterized by a high body temperature, usually a core body temperature above 40°C, and signs of central nervous system dysfunction, such as abnormal behavior, confusion, seizures, or loss of consciousness.

Heatstroke is often accompanied by multiple organ failure, including encephalopathy, acute liver failure, kidney failure, pulmonary edema, cardiomyopathy, heart failure, acute respiratory distress syndrome, disseminated intravascular coagulation, and rhabdomyolysis. It has a very high mortality rate and is one of the most challenging heat-related conditions to treat clinically.

The terms “heat exhaustion” and “heatstroke” are often confused by the general public. Mild heat-related illness may sometimes be incorrectly described as heatstroke, while severe and life-threatening heatstroke may be mistaken for heat exhaustion.

Heatstroke can be divided into two categories:

1. Classic heatstroke:
2. This type is mainly caused by impaired heat dissipation in a hot environment. It most commonly occurs in older adults, particularly those with chronic illnesses or impaired heart and lung function.
3. Exertional heatstroke:
4. This type is caused by intense physical activity in a hot environment, during which the body generates heat faster than it can dissipate it. It is commonly seen in athletes, outdoor workers, and newly enlisted military personnel.

High-Risk Groups for Heat-Related Illness

Body heat is affected not only by the external environment but also by the amount of heat generated within the body and the body’s ability to dissipate heat. The following individuals and situations are associated with a higher risk of heatstroke:

1. People who are overweight or have a high body mass index (BMI):
2. A thicker layer of subcutaneous fat and reduced circulation beneath the skin may make it more difficult for the body to release heat.
3. Outdoor workers and athletes:
4. When strenuous activity exceeds a person’s physical capacity, the body may generate large amounts of heat that cannot be dissipated quickly enough, leading to heat accumulation and heat-related illness.
5. People who do not drink enough fluids:
6. Sweating is essential for heat dissipation and requires an adequate supply of water.
7. People who are physically weakened:
8. Conditions such as lack of sleep, a cold, diarrhea, infection, or fever may impair circulation to the skin and reduce sweating.
9. People who have not adapted to hot environments:
10. Newly enlisted military personnel, new athletes, and inexperienced outdoor workers require a period of heat acclimatization. This process generally takes approximately 7 to 14 days, during which exposure time and training intensity should be increased gradually. Sudden exposure to the same workload as experienced personnel without proper acclimatization greatly increases the risk of heatstroke.
11. People taking medications that inhibit sweating, diuretics, or sympathomimetic drugs:
12. Some cold medicines containing antihistamines, gastrointestinal medicines containing anticholinergic agents, and certain psychiatric medications may reduce sweating. Diuretics may cause dehydration. Sympathomimetic substances, such as amphetamines, MDMA, and ephedrine, may increase heat production in the body.
13. People with chronic illnesses or impaired heart and lung function:
14. Good circulation to the skin is necessary for heat dissipation. Poor cardiopulmonary function may therefore reduce the body’s ability to release heat.
15. Highly competitive individuals who tend to exceed their physical limits:
16. During competitions, some people may exercise beyond their physical capacity in order to win. The risk of heatstroke is even greater if they have not slept well, stayed up late, or experienced diarrhea the previous day.
17. People with psychiatric disorders, cognitive impairment, or dementia:
18. These individuals may be unable to correctly recognize or respond to a hot environment, such as by leaving the area or drinking more water. They are therefore at increased risk of heat-related illness when outdoors during summer.
19. People with metabolic disorders:
20. Conditions such as hyperthyroidism increase the metabolic rate and the amount of heat produced by the body.
21. Older adults over 65 years of age and young children under 5 years of age:
22. Their ability to regulate body temperature and dissipate heat may be less effective, making them more susceptible to heat-related illness during hot weather.

Treatment and Prevention of Heat-Related Illness

The primary principle in treating heat-related illness is to lower the patient’s body temperature as quickly as possible. Conductive cooling is the fastest cooling method, followed by evaporative and convective cooling.

When a person with suspected heat-related illness is found, immediately move the person to a cool or shaded area and loosen or remove unnecessary clothing. If possible, immerse the body below the neck in a tub of cold water. Alternatively, wet the body with cool or ice-cold water and use a fan to enhance evaporative cooling.

Ice packs or cold towels may also be placed on the neck, under the armpits, and over the groin, where major blood vessels are located. The patient should then be transported to a medical facility as soon as possible in an air-conditioned vehicle. Cooling measures should be continued throughout transportation.

The prevention of heat-related illness should focus on reducing risk factors and becoming familiar with appropriate cooling measures:

1. Avoid prolonged outdoor activity in hot and humid conditions:
2. Avoid staying outdoors or exercising when both temperature and humidity are high. When outdoor work or exercise is unavoidable, rest periods and fluid intake should be adjusted according to the heat index. The higher the heat index, the more frequent and longer the rest periods should be, and the more fluids should be consumed.
3. Wear appropriate clothing during summer:
4. When outdoors, wear loose-fitting, breathable, light-colored clothing that allows sweat to evaporate easily. Wear a wide-brimmed hat or use an umbrella to reduce exposure to radiant heat from the sun.
5. Adjust workloads for outdoor workers:
6. Outdoor workers who are at high risk of heat-related illness should have their workload adjusted in hot environments. Individual differences in physical fitness should also be considered.
7. Allow time for heat acclimatization:
8. Newly enlisted military personnel, new members of sports teams, and new outdoor workers should undergo a gradual period of heat acclimatization before performing strenuous activity in hot environments.
9. Maintain adequate hydration during physical activity:
10. Drink sufficient fluids during hot weather. When not exercising, drink approximately 200–300 mL of water every 30 minutes. During exercise, drink approximately 200–300 mL every 15–20 minutes. Avoid beverages containing large amounts of sugar, caffeine, or alcohol, as these may increase urination and contribute to dehydration.
11. Review medication use:
12. Be aware of medications that may increase the risk of heat-related illness, including cold medicines, diuretics, anticholinergic drugs, sedatives, ephedrine, and amphetamines.
13. Protect family members with dementia or cognitive impairment:
14. During extremely hot weather, do not allow family members with dementia or cognitive impairment to go outdoors alone.
15. Never leave infants or young children alone in a parked vehicle:
16. Never leave a child unattended in a vehicle without air conditioning, especially when it is parked in direct sunlight. The temperature inside a vehicle can rise rapidly and cause severe heat-related illness within a short period.
17. Monitor vulnerable individuals:
18. Pay close attention to older adults, infants, young children, and family members with chronic illnesses, and watch for signs and symptoms of heat-related illness.

Severe heat-related illness may progress to heatstroke and multiple organ failure and can have a very high mortality rate. However, heat-related illness is largely preventable. By understanding its causes, recognizing its warning signs, and taking appropriate preventive measures, many serious and potentially fatal incidents can be avoided.

Source: Health Promotion Administration, Ministry of Health and Welfare — Heat-Related Illness Prevention and Health Education Resources

https://www.hpa.gov.tw/Pages/List.aspx?nodeid=440