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Health effects of Extreme Heat Events

Learn how to protect yourself and your family in an extreme heat event.

People with underlying health conditions (e.g. respiratory, cardiovascular) may notice their condition gets worse, while some may experience heat stroke that could result in death. Extreme heat events can lead to one or more of the following health effects, in decreasing order of severity:

Heat stroke: The most serious type of heat illness is a result of body heat overload. Signs of heat stroke may include a core body temperature of more than 40°C/104°F.
Heat exhaustion: Caused by excessive loss of water and salt. Symptoms may include heavy sweating, weakness, dizziness, and nausea.
Heat fainting (also called parade syncope): Caused by the loss of body fluids through sweating and by lowered blood pressure due to pooling of blood in the legs.

Heat-Vulnerable Groups

Those who are more at-risk from the impacts of extreme heat are:

  1. Older adults
  2. Infants and young children 
  3. People with chronic illness or who are physically impaired
  4. Socially disadvantaged individuals and communities
  5. Occupational groups (e.g. construction workers, highway maintenance workers, miners)

Health risks from extreme heat may be compounded for those with more than one risk factor.

What should I do to protect myself from extreme heat?

  • Watch for the effects of heat illness: swelling, rash, cramps, fainting, heat exhaustion, heat stroke and the worsening of some health conditions.
  • Outdoor workers should take regularly scheduled breaks in a cool place.
  • Avoid sun exposure. Shade yourself by wearing a wide-brimmed, breathable hat, find a tree-shaded area or consider using an umbrella to shade yourself from the sun.
  • Drink plenty of cool liquids, especially water, before you feel thirsty to decrease your risk of dehydration. Thirst is not a good indicator of dehydration.
  • Ask a health professional how medications or health conditions can affect your risk in the heat.
  • Check on older family, friends and neighbours. Make sure they are cool and drinking water.
  • Never leave people or pets inside a parked vehicle.
  • Seek a cool place such as a tree-shaded area, cool shower or bath, or air-conditioned public building, if one exists in your community.
  • When it’s hot eat cool, light meals.
  • Keep your home cool.  Block the sun by closing curtains or blinds.
  • Watch for the symptoms of heat illness: dizziness/fainting; nausea/vomiting; rapid breathing and heartbeat; extreme thirst; decreased urination with unusually dark urine.

Heat and Wildfires

Extreme heat events often coincide with wildfire events. Learn about the health effects of wildfire smoke.

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