Extreme Heat and Humidity

While it is important to enjoy the outdoors during Canadian summers, it is also important to remember that extreme heat and humidity may cause serious health effects. How this mix of hot and humid weather feels to the average person is called the humidex.

When there is elevated heat and humidity, Environment Canada issues a Humidex Advisory.

Extreme Heat and Humidity Fact Sheet


Public health concern

Extreme heat and humidity can be a health threat because the body retains more heat when the weather is both hot and humid. This kind of weather also causes people to feel hot and sticky, with higher humidity generally causing higher discomfort. While everyone is at risk of heat illnesses from extreme heat, these risks are greatest for:

  • Older adults
  • Infants and young children
  • People with chronic illnesses, such as breathing difficulties, heart conditions, or psychiatric illnesses
  • People who work in the heat
  • People who exercise in the heat
  • People who are homeless
  • People who live alone

Obesity, dehydration, fever or infection, sunburn, and alcohol use also increase peoples' risk from extreme heat.

Heat stroke is a medical emergency.

Call 911 immediately if you are caring for someone who has a high body temperature and is either unconscious, confused, or has stopped sweating.
 

While waiting for help, cool the person right away by:

  • Moving them to a cool place
  • Applying cold water to large areas of the skin or clothing
  • Fanning the person as much as possible

Heat illnesses include heat stroke, heat exhaustion, heat cramps (muscle cramps), heat edema (swelling of hands, feet and ankles), and heat rash.

Some symptoms of heat illness are:

  • Dizziness or fainting
  • Nausea or vomiting
  • Headache
  • Rapid breathing and heartbeat
  • Extreme thirst
  • Decreased urination with unusually dark yellow urine




How to reduce your risk from extreme heat and humidity

The facts below are from Health Canada's Climate Change and Health resources.

Older adults:

Adhere to Health Canada's older adult-specific advice.

Caregivers of children:

Adhere to Health Canada's children-specific advice.

People who work or exercise in the heat:

Adhere to Health Canada's advice for people who are active in the heat.

Health care workers:

Visit Health Canada's ExtremeHeat.ca website and adhere to their factsheets with health care worker-specific advice.

Everyone:

  • Watch for the symptoms of heat illness. If you or someone you know experiences any of these symptoms during extreme heat, immediately move to a cool place and drink liquids. Cool (not ice-cold) water is best.
  • 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. Avoid drinks that are high in sugar, caffeine and/or alcohol, as they can increase the amount of water lost by the body.
  • Avoid sun exposure. Wear sunscreen of SPF 15 or higher. Shade yourself by wearing a wide-brimmed, breathable hat or using an umbrella.
  • Wear loose-fitting, light-coloured clothing made of breathable fabric.
  • Reschedule or plan outdoor activities during cooler parts of the day.
  • Take a break from the heat by spending a few hours in a cool place. It could be a tree-shaded area, swimming facility or an air-conditioned spot such as a public building or shopping mall.
  • Take cool showers or baths (or cool down with cold, wet towels) until you feel refreshed.
  • Block sun out by closing awnings, curtains or blinds during the day.
  • Prepare meals that don't need to be cooked in your oven.
  • Never leave people or pets in your care inside a parked vehicle or in direct sunlight.
  • Frequently visit neighbours, friends and older family members, especially those who are chronically ill, to make sure that they are cool and hydrated.
  • If you are taking medication or have a health condition, ask your doctor or pharmacist if it increases your health risk in the heat and follow their recommendations.

Please see Health Canada for more extreme heat-related health information and Environment Canada for Humidex Advisories.
 

Contact(s)

Region of Waterloo Public Health
General Inquiries
99 Regina Street South, Waterloo, Ontario N2J 4V3

Phone: 519-575-4400
TTY: 519-575-4608

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