How Does Extreme Heat Affect Health? Heat Stroke, Symptoms and Prevention

High temperatures and humidity can make it more difficult for the body to maintain a safe core temperature. The body normally cools itself mainly through sweating and increased blood flow to the skin.

When temperatures and humidity become very high, sweat may not evaporate efficiently. Heat can then accumulate in the body and lead to heat-related illness.

Humidity matters. Sweating alone does not cool the body effectively; sweat must evaporate from the skin. High humidity can reduce evaporation and increase heat stress.

How Does Extreme Heat Affect the Body?

During heat exposure, the body increases sweating and blood flow to the skin in an attempt to release heat.

Prolonged or severe exposure can result in:

  • Fluid and electrolyte loss
  • Dehydration
  • Low blood pressure
  • Dizziness or fainting
  • Heat cramps
  • Heat exhaustion
  • Heat stroke

Severe heat stroke can damage the brain, kidneys, liver, cardiovascular system and other organs.

Who Is at Higher Risk From Extreme Heat?

Anyone can develop heat-related illness, but the risk is higher for:

  • Older adults
  • Babies and young children
  • Pregnant women
  • People with cardiovascular disease
  • People with chronic lung or kidney disease
  • People with diabetes
  • People with certain neurological or psychiatric conditions
  • People with obesity
  • Outdoor and heat-exposed workers
  • Athletes and people performing strenuous physical activity
  • People who require assistance with daily care
  • People living alone without adequate access to cooling

Certain medicines, including some diuretics, blood-pressure medicines and psychiatric medicines, can also affect fluid balance or the body's response to heat.

Do not stop or change prescribed medicines on your own during hot weather. People with heart or kidney disease should follow individual medical advice regarding fluid intake and medication.

What Is Heat Exhaustion?

Heat exhaustion can develop when the body loses substantial amounts of water and salt through sweating.

Symptoms can include:

  • Heavy sweating
  • Headache
  • Dizziness
  • Weakness
  • Thirst
  • Nausea
  • Muscle cramps
  • Reduced urine output

The person should stop activity, move to a cool environment, remove unnecessary clothing and begin cooling. If fully alert and able to drink safely, fluids can be given.

What Is Heat Stroke?

Heat stroke is a life-threatening condition characterised by severe overheating together with neurological dysfunction.

Warning signs can include:

  • Confusion or altered behaviour
  • Loss of coordination
  • Fainting
  • Seizures
  • Very high body temperature

Heat stroke is a medical emergency. Call emergency medical services, move the person to a cooler environment and begin rapid cooling. Do not give fluids by mouth to a person with impaired consciousness.

A person with heat stroke does not necessarily stop sweating. People with exertional heat stroke may still have wet, sweaty skin.

How Can You Protect Yourself From Extreme Heat?

  • Avoid unnecessary exposure during the hottest part of the day.
  • Stay in the shade and take regular breaks when outdoors.
  • Wear light, loose-fitting clothing.
  • Use a wide-brimmed hat and UV-protective sunglasses.
  • Use appropriate sunscreen on exposed skin.
  • Drink water regularly throughout the day.
  • Move strenuous exercise to cooler times of day.
  • Use cool showers, baths or damp cloths to cool the skin.
  • Regularly check on older or vulnerable relatives and neighbours.

How Much Water Should You Drink in Hot Weather?

Fluid requirements generally increase when sweating increases.

The World Health Organization gives approximately 2–3 litres of water per day as a practical general guide for many adults during hot weather, but this should not be treated as a universal prescription.

Requirements vary according to activity, body size, sweating, humidity and medical conditions.

People with heart or kidney disease who have been advised to restrict fluids should not simply increase their intake because the weather is hot. They should follow personalised medical advice.

What Should You Eat and Drink in Hot Weather?

Water should be the main drink for hydration.

Foods with a high water content can also contribute to overall fluid intake.

It is advisable to limit excessive:

  • Alcohol
  • Sugary drinks
  • Caffeine

Fruit juice and sports drinks are not routinely required as substitutes for water.

Extra salt is also not routinely required for everyone. People who exercise or work intensely for prolonged periods in heat may have different electrolyte needs, while excessive salt can be harmful for people with hypertension, heart disease or kidney disease.

How Should You Exercise in Hot Weather?

  • Exercise during cooler morning or evening periods.
  • Reduce intensity when temperatures are high.
  • Drink water regularly.
  • Wear light, breathable clothing.
  • Increase exposure gradually if you are not acclimatised to the heat.

Stop exercising and move to a cool place if you feel faint, unusually weak or dizzy.

How Can You Keep Your Home Cool?

  • Close blinds, curtains or shutters on sun-facing windows during the day.
  • Ventilate when the outdoor temperature is cooler, particularly overnight and early in the morning.
  • Turn off unnecessary electrical equipment.
  • Use air-conditioned or cooler environments when available.
  • Use cool showers or damp cloths to cool the body.

Never leave a baby, child, vulnerable adult or animal alone in a parked vehicle. Temperatures inside a vehicle can rapidly reach dangerous levels.

Which Symptoms Require Emergency Care?

Seek emergency medical help when heat exposure is accompanied by:

  • Confusion or altered mental state
  • Abnormal behaviour
  • Loss of coordination
  • Collapse or fainting
  • Seizures
  • Very high body temperature

Move the person away from heat and begin active cooling while emergency medical assistance is being arranged.

Have Heat-Related Symptoms Assessed

Dizziness, severe fatigue, dehydration or difficulty tolerating heat alongside a chronic medical condition can be medically assessed.

Frequently Asked Questions

How does extreme heat affect the body?
Extreme heat and high humidity can make it difficult for the body to cool itself through sweating and evaporation. This can lead to dehydration, heat cramps, heat exhaustion and potentially life-threatening heat stroke.
What is the most important warning sign of heat stroke?
Altered mental state is one of the key features that distinguishes heat stroke from milder heat illness. Confusion, abnormal behaviour, poor coordination, collapse or seizures require emergency medical attention.
Does sweating always stop during heat stroke?
No. Skin may be hot and dry in classic heat stroke, but people with exertional heat stroke can continue sweating. The presence of sweating therefore does not rule out heat stroke.
How much water should you drink during hot weather?
WHO gives around 2–3 litres of water throughout the day as a practical general guide for many adults during hot weather. Individual needs vary with body size, sweating, activity and health. People with heart or kidney disease who have fluid restrictions should follow their doctor's advice.
Do you need extra salt in hot weather?
Not routinely. People who sweat heavily for prolonged periods may have greater electrolyte requirements, but excess salt can be harmful for people with hypertension, heart disease or kidney disease.
Can you drink coffee during hot weather?
Moderate caffeine intake is not necessarily prohibited for healthy adults, but water should remain the main source of hydration and excessive caffeine, alcohol and high-sugar drinks should be limited.
Can air conditioning help prevent heat-related illness?
Yes. Spending time in a cooler or air-conditioned environment can reduce heat stress during extreme temperatures. Access to cooling is particularly important for older people and those with chronic medical conditions.
Academic Hospital note: Fluid and salt requirements vary between individuals during hot weather. People with heart disease, kidney disease or hypertension should not change their fluid intake or medication without medical advice. You can book an appointment.

References

  1. Republic of Türkiye Ministry of Health. Protection From Extreme Heat
  2. World Health Organization. Heat and Health
  3. World Health Organization. Heatwaves: How to Stay Cool
  4. Centers for Disease Control and Prevention. Heat-related Illnesses