During heat waves, it is harder for your body to cool and maintain its temperature within normal limits. During these waves, prolonged exposure to heat, excessive physical effort or very heavy sweating can have certain effects on health.

Symptoms that Require Monitoring Changes in Health


It is important to monitor any deterioration in the health of an adult with the following symptoms:

  • Headaches
  • Muscular cramps
  • Swollen hands, feet and ankles
  • Apparition of small red pimples (heat rash) on your skin
  • Unusual fatigue or exhaustion
  • General discomfort
  • Signs of dehydration:
    • Excessive thirst
    • Less frequent need to urinate
    • Dark urine
    • Dry skin
    • Rapid pulse and breathing

If you have questions regarding your health, call Info-Santé 811 or consult with a health professional, a pharmacist for instance.

When to consult

Other symptoms require immediate medical intervention, meaning within 2 hours. An adult with one or more of the following symptoms must promptly be taken to emergency or 9‑1‑1 called on their behalf:

  • Difficulty breathing
  • Convulsions (stiffness of the body and jerky, involuntary muscle contraction)
  • Deterioration of consciousness:
    • Confusion
    • Unusual behaviour
    • Agitation
    • Hallucinations
    • Lack of response to stimuli
  • Loss of consciousness
  • Signs of heat stroke:
    • Temperature over 39.5 ºC (103.1 ºF) with an oral thermometer or over 40 ºC (104 ºF) with a rectal thermometer
    • Dry skin, hot and red or cold and pale
    • Dizziness and vertigo
    • Confused and illogical speech
    • Aggressiveness or bizarre behaviour
    • General discomfort

Heat stroke is the most serious effect of heat. It can occur suddenly and quickly lead to death if not treated.

Babies or Children

Certain symptoms may indicate complications linked to heat:

  • Dry skin, lips or mouth
  • Abnormal skin colour (red or pale)
  • Headaches
  • Sunken eyes with dark rings
  • Dark and smaller quantity of urine
  • Vomiting and diarrhea
  • Unusual restlessness, irritability or confusion
  • Difficulty breathing
  • Drowsiness, prolonged sleep and difficulty waking up
  • Body temperature greater than 38.5 ºC (101.3 ºF) with a rectal thermometer or over 37.5 ºC (99.5 ºF) with an oral thermometer (Note: Using an oral thermometer to take the temperature of new-borns, babies and children under 5 years old is not recommended.)

When to Consult

The deterioration of a child’s health, especially the very young, can be quick and difficult to notice. When a baby or child shows symptoms, a medical consultation is usually necessary. If you are unsure, contact Info-Santé 811. In an emergency, call 9‑1‑1.

Protection and Prevention

You can take certain precautions to prevent the effects of heat, such as hydrating yourself well and refreshing yourself often. Further advice to ensure the well-being of you and your loved ones during heat waves is available on the Preventing the Effects of Heat page.

Risk Factors

There are greater risks of feeling discomfort due to heat:

  • When humidity is high
  • When there is light wind or none at all
  • When a wave of heat occurs and the body has yet to be acclimatised to the heat, such as early in the season or immediately after cooler temperatures
  • In cities, where the temperatures are generally higher than in the countryside

People at Risk

Certain people are more at risk of developing complications if exposed to oppressive or extreme heat:

  • Babies and kids younger than 5 years old
  • Seniors
  • People with reduced autonomy or that live alone
  • People suffering from chronic illnesses or severe mental health problems
  • People with drug or alcohol addictions
  • People with physically demanding jobs or that work in the sun or outdoors, such as construction workers
  • People that work in places where processes emit heat, such as foundries and bakeries
  • People doing intense physical exercise outside in hot weather or indoors in places with no air-conditioning or that are poorly ventilated
  • People without access to cool or air-conditioned places