What is the difference between heat exhaustion and heat stroke?
The main difference lies in the severity of the symptoms. Heat exhaustion is characterized by thirst, excessive sweating, dizziness, nausea, irritability, and a mild fever. In older adults, we may also observe falls, fainting episodes (lipotimies), confusion, drowsiness, and worsening of chronic medical conditions.
Heat stroke occurs when this situation is not stopped. It represents a failure of the body's temperature regulation system. Symptoms include a body temperature above 40°C (104°F), confusion, seizures, coma, and the involvement of multiple organs.
When should you call emergency services because of the heat?
During periods of persistently high temperatures over several days, severe heat-related illness is most likely to occur in vulnerable populations, especially very young children and older adults who may be unable to care for themselves adequately (drinking water, seeking cooler environments, etc.).
Warning signs include drowsiness, confusion, worsening of chronic diseases, a marked reduction in food and fluid intake, vomiting, or high fever accompanied by a decreased level of consciousness.
It is important to remember that these symptoms can also occur in relatively young, healthy individuals after strenuous physical activity in high temperatures.
What symptoms mean you should go to the emergency department?
The symptoms mentioned above—drowsiness, confusion, worsening of chronic illnesses, significantly reduced intake, vomiting, and high fever with decreased consciousness—should be taken seriously, especially if the condition does not improve after hydration and cooling measures at home.
Medical attention is also recommended if vomiting prevents adequate hydration.
Why is it not recommended to place someone with heat stroke in very cold water?
Because the body's temperature-regulating center is already overwhelmed. Exposing the person to extreme cold may trigger thermal shock, which can lead to cardiovascular collapse.
Can you suffer heat stroke without being directly exposed to the sun?
Yes. Heat stroke is caused by excessive heat exposure, regardless of whether a person is in direct sunlight. Being under the sun may accelerate its onset, but prolonged exposure to high temperatures is what ultimately causes heat stroke.
What happens when heat stroke becomes complicated? Can it cause multiple organ failure?
Yes. If heat stroke is not treated promptly and appropriately, it can lead to failure of multiple organs, including the kidneys, respiratory system, cardiovascular system, digestive system, and brain. This is an extremely serious and potentially life-threatening situation.
What should you do if heat-related symptoms do not improve after an hour?
A lack of improvement after one hour may indicate that the person has been exposed to heat for a prolonged period and/or is not receiving sufficient hydration and cooling.
Cooling and hydration measures should be continued for a while longer to assess whether gradual improvement occurs.
If symptoms worsen, emergency services should be contacted immediately, or the person should be taken to the emergency department.
What mistakes are commonly made when someone has heat stroke?
- Keeping the person in the same hot environment without improving ventilation or temperature conditions.
- Applying wet clothing without adequate ventilation (which can create a sauna effect).
- Giving very cold drinks.
- Administering medications to reduce fever (these are ineffective and may damage organs).
- Forcing an unconscious person to drink.
- Cooling the body with ice or extreme cold.
Content developed with Dr. Elisenda Gómez, specialist in the Emergency Department at Hospital Clínic Barcelona.
Medical review: June 2026
Last updated: June 2026
