The Effects of Extreme Heat on Physical Health

What effects does heat have on health?

In adults

Monitor symptoms closely. If you notice a deterioration in the person’s condition, consult a pharmacist or call Info-Santé 811.

  • Headaches
  • Small red pimples on the skin (heat rash)
  • Dehydration:
    • Dry skin
    • Intense thirst
    • Rapid pulse and breathing
    • Less frequent need to urinate
    • Dark urine
  • Generalized malaise and unusual exhaustion or fatigue
  • Swollen hands, feet, and ankles
  • In children and babies

    A young child’s health can deteriorate rapidly. If in doubt, call Info-Santé 811. A medical consultation is often necessary.

    • Headaches
    • Hollow, ringed eyes
    • Dry skin, lips, or mouth
    • Pale or red skin (abnormal colour)
    • Difficulty breathing
    • Vomiting and diarrhea
    • Drowsiness, prolonged sleep, difficulty waking up
    • Irritability, confusion, agitation
    • Dark urine in smaller quantity
    • Temperature over 38.5°C (101.3°F) (rectal thermometer), or over 37.5°C (99.5°F) (oral thermometer)


Other symptoms are more severe and require the intervention of a healthcare professional within 2 hours.

  • Heatstroke
    • Temperature over 39.5°C (103.1°F)
    • Generalized malaise
    • Dizziness or vertigo
    • Confusing, illogical speech
    • Bizarre or aggressive behaviour
    • Dry, red, and warm skin or pale and cold
  • Difficulty breathing
  • Loss of consciousness
  • Convulsions
  • Impaired consciousness
    • Unusual behaviour
    • Confusion
    • Agitation
    • Hallucinations
    • No response to stimuli

Information taken from the website.

When are the risks higher?

Certain factors increase the risk of heat discomfort:

  • The heat lasts for several days.
  • High humidity.
  • A weak or non-existent wind.
  • High night temperatures.
  • High temperatures early or later in the season, when the body isn’t accustomed to the heat.
  • Large cities, where the temperature felt is higher than in the countryside.

Who is most at risk?

Some people are at a higher risk of developing complications as a result of exposure to extreme heat:

  • Children under 5 years old and babies.
  • People aged 85 and over.
  • People with loss of autonomy.
  • Pregnant women.
  • People who are overweight, in poor physical condition, suffer from chronic diseases or severe mental health problems.
  • People with problems with drug or alcohol use or taking medications that can aggravate the effects of heat.
  • People who do not have access to cool or air-conditioned areas are doing intense physical activity outdoors or are in poorly ventilated areas.
  • People whose workplace is warm or hot, such as foundries, or working outdoors doing physically demanding work.

The Relationship Between Heat and Mental Health

The effect of heat on mental health

Studies show that heat waves result in:

  • Lack of concentration
  • Violence and aggressiveness
  • Lack of sleep
  • Depression
  • Substance abuse
  • Lack of energy

Aggressiveness, irritability, and internal temperature

Some researchers attribute aggressiveness to internal temperature.

Feelings of frustration come from within and, therefore, can cause an increase in the internal temperature of the body. People struggling to control their external heat, will find it more difficult to control their inner state.

The inability to cool off triggers a state of “fight or flight”. This state is reflected in two ways: The person fights against the threat or flees from it at all costs. If the person cannot escape the heat, they go into “fight” mode, becoming aggressive and fighting the discomfort.

A study by Craig A. Anderson and Matt DeLisi in 2011 illustrates the correlation between heat and aggressiveness in people. They compared FBI data on violent and non-violent crime from 1950 to 2008 with average annual temperatures in those same years. They noted that the number of violent crimes increased with warm temperatures. They estimated that an average increase of 1°C would result in a 6% increase in violent crime, resulting in an additional 25,000 serious or fatal assaults per year in the United States alone.

In anger control therapies, teachers demonstrate, among other things, how to regulate the internal temperature through breathing and relaxation exercises. This allows people to manage their aggressive behavior better.

Heat and lack of sleep

Late in the afternoon and evening, the body begins to produce less internal heat.

Existing heat is pushed into the extremities and then released from the body. This process aims to reduce body temperature, which, in turn, leads to fatigue and then sleep.

Body temperature remains low overnight and begins to rise early in the morning, preparing you to wake up. During a heat wave, the body finds it more challenging to get rid of its internal heat, which leads to insomnia or poor sleep quality.

Lack of sleep can have a significant impact on people’s moods and behaviour. It can lead to the appearance of symptoms of depression, which can cause aggression, lack of concentration, and lack of energy.

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The snowball effect of heat waves

Research by Connor Y. H. Wu, Benjamin F. Zaitchik and Julia M. Gohlke depicts the relationship between heat waves and car accidents. Research results show a 3.4% increase in fatal car accidents during heat waves.

These periods of intense heat cause sleep disturbances that cause fatigue and drowsiness, which results in slower reaction times.

The U.S. National Highway Traffic Safety Administration estimates that at least 100,000 collisions per year are caused by fatigue. Not all cases are caused by heat waves, of course, but the risk is increased when temperatures are high.

The goal here is not to lay all the blame on heat waves. However, heat waves create a context conducive to increased violent altercations, accidents, heat-related illnesses, worsening of pre-existing conditions, and more.

How to Manage Heat Waves

Due to global warming, heat waves will only increase. How to can you protect yourself? The following suggestions will help. Be sure you keep an eye on your children and take the lead in assisting them to stay cool.

Refresh yourself

  • Look for cool or air-conditioned places and frequent them as often as possible.
  • Wet your skin with the help of a cool towel several times a day.
  • Take a lukewarm shower as many times as necessary.

Protect yourself

  • Wear light clothing.
  • Wear a wide-brimmed hat.
  • Reduce physical effort.
  • Limit outdoor activities when the temperatures are very high.
  • Never leave a child alone in a car or a poorly ventilated room.

Stay hydrated

  • Drink plenty of water throughout the day.
  • Avoid drinking alcohol which has a dehydrating effect.

Control your indoor temperature as best you can

  • Close curtains and blinds to block direct sunlight.
  • Open windows at night to ventilate your home if the temperature drops.
  • Use fans and an air conditioning unit to keep your home at a comfortable temperature during the day, especially in bedrooms.

MST is a Quebec company that sells, installs, and maintains air conditioning units and heat pumps. Contact us to find the right system to keep you comfortable during the next heat wave.

By following the tips found in this article and using an air conditioning unit adapted to your home, you’ll be well equipped to get through any heat wave!

*Document for informational purposes only. Refer to a healthcare professional for any doubt about your physical or mental health.