Find out about health effects of extreme heat events

During an extreme heat event

People may notice their health gets worse or they may experience heat stroke if they have underlying conditions such as:

  • respiratory; and
  • cardiovascular conditions.

In extreme cases, heat stroke can result in death.

Effects of extreme heat

Extreme heat events can lead to 1 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

Onset of symptoms  can be sudden or gradual. These may include:

  • a core body temperature of more than 40°C/104°F:
  • other symptoms:
    • red, dry or damp skin;
    • headache; and
    • dizziness.

Heat exhaustion

  • Caused by excessive loss of water and salt.
  • Symptoms of heat exhaustion 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.

The basic symptom of heat fainting or syncope is fainting, with or without mental confusion.

Watch for these effects of heat illness:

  • swelling;
  • rash;
  • cramps;
  • fainting;
  • heat exhaustion;
  • heat stroke; and
  • the worsening of some health conditions.

Watch for these symptoms of heat illness:

  • dizziness/fainting;
  • nausea/vomiting;
  • rapid breathing and heartbeat;
  • extreme thirst; and
  • decreased urination with unusually dark urine.

Heat-vulnerable groups

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

  • older adults;
  • infants and young children;
  • people with chronic illness or who are physically impaired;
  • socially disadvantaged individuals and communities; and
  • occupational groups (e.g., construction workers, highway maintenance workers, miners).

Health risks from extreme heat may be compounded for those with more than 1 risk factor.

Protection from extreme heat

Here is a list of things that you can do to protect yourself from extreme heat.

  • Take regularly scheduled breaks in a cool place.
    • Especially if you are an outdoor worker.
  • Avoid sun exposure:
    • shade yourself by wearing a wide-brimmed, breathable hat; or
    • 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 it exists in your community.
  • When it’s hot eat cool, light meals.
  • Keep your home cool.
    • Block the sun by closing curtains or blinds.

Heat and wildfires

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

Related information

Learn more.