Ministry Programs

Extreme Heat

Extreme temperatures and high humidity pose a significant health risk to Ontarians. Anyone can suffer heat-related illness when their bodies are unable to properly cool. It's important to be aware of who is at greatest risk and what actions can be taken to prevent a heat-related illness or death.

Are You at Risk?

During a heat wave, everyone is at risk, but some groups are more vulnerable than others. They include:

• infants and young children
• older adults
• people with chronic medical conditions (e.g. heart disease, respiratory conditions, diabetes, etc.) or mental illnesses (e.g. depression or dementia)
• people on certain types of medications ( for high blood pressure, depression, insomnia, etc.)
• homeless people
• people with limited mobility
• people who exercise vigorously outdoors (play sports, cyclists, gardeners)
• outdoor workers (depending upon length or time and exertion levels)^†
• people who work in places where heat is emitted through industrial processes (e.g., foundries, bakeries, dry cleaners) ^†

^†Please see the Ministry of Labour's Website for further advice

Health Risks of Extreme Heat: Know When to Get Help

You can become ill when you are exposed to too much heat, especially if you are doing too much for your age and physical condition.

Adverse health effects that can occur as a direct result of exposure to excessive heat include:

• heat cramps: symptoms/signs include painful muscular cramps, usually in the legs or abdomen
• heat edema: symptoms/signs include swelling of hands, feet and ankles
• heat exhaustion: symptoms/signs include heavy sweating, weakness, dizziness, nausea, vomiting, fainting.
• heat stroke: symptoms/signs include headache, dizziness, confusion or other altered mental state and fainting. Skin may be hot and dry, or the individual may be sweating due to high body temperature. This is a medical emergency that can prove fatal.

Increases in other health problems can also be seen, especially for those with other chronic medical conditions such as heart conditions.

Consult your physician, a healthcare provider or call Telehealth Ontario (1-866-797-0000 or TTY at 1-877-797-0007) if you experience any of the above symptoms. Call 911 or your local emergency number immediately if you are caring for a someone, such as a neighbour, who has a high body temperature and is either unconscious, confused or has stopped sweating.

Things You Can Do to Protect Yourself

Prepare for the heat in advance

• watch local weather forecasts and alerts:
  • Check the Environment Canada Weather Information website for information regarding weather and humidex reports.
  • Check the Air Quality Health Index website for information regarding smog alerts.
• arrange for regular visits by family members, neighbours or friends during very hot days in case you need assistance. Visitors can help identify signs of heat illness that could be missed over the phone.
• if you have an air conditioner, make sure it works properly before the hot weather starts.
• learn about ways to keep your home cool during the summer. If you live in a house, plant trees on the side where the sun hits the house during the hottest part of the day. If you live in an apartment or condo, you can block the sun by closing curtains or blinds during the day. If safe, open your windows at night to let cooler air into your home.

Protect your health during extreme heat

Watch for symptoms of heat illness:

• dizziness or fainting
• nausea or vomiting
• headache
• rapid breathing and heartbeat
• extreme thirst (dry mouth or sticky saliva)
• decreased urination with unusually dark yellow urine
• changes of behaviour in children (like sleepiness or temper tantrums)

If you have any of these symptoms during extreme heat, immediately move to a cool place and drink liquids. Water is best.

Stay hydrated:

• drink plenty of cool liquids (especially water) before you feel thirsty to decrease your risk of dehydration (not having enough fluids in your body). Thirst is not a good indicator of dehydration
• drink water before, during and after a physical activity
• remind yourself to drink water by leaving a glass by the sink
• avoid beverages such as alcohol, coffee, tea or cola
• eat more fruits and vegetables as they have a high water content

How to stay cool

Dress for the weather

• wear loose-fitting, light-coloured clothing and a wide-brimmed hat made of breathable fabric

Take a break from the heat

• if you must do physical activity in extreme heat, take extra breaks, remove gear to let your body cool off and drink lots of water. Hot weather can affect how you perform normally. Give your body time to recover after being in the heat
• take cool baths or showers periodically to cool down

Keep your home cool

• eat light, cool foods, and try to avoid using the oven or other hot appliances
• keep indoor lights low or turned off
• block the sun by closing awnings, curtains or blinds during the day
• if safe, open your windows at night to let cooler air into your home
• if you have an air conditioner with a thermostat:
  • keep it set to the highest setting that is comfortable (somewhere between 22°C/72°F and 26°C/79°F).
  • if you are using a window air conditioner, cool only one room where you can go for heat relief

If your home is extremely hot

• take cool showers or baths until you feel refreshed
• use a fan to help you stay cool and aim the air flow in your direction.
• spend a few hours in a cool place such as:
  • a tree-shaded area
  • public spaces such as a swimming facility
  • an air-conditioned space like shopping mall, grocery store, library, or community centre, or a specially designated facility

Avoid exposure to extreme heat when outdoors

• never leave people or pets inside a parked vehicle or in direct sunlight
• when the outside air temperature is 23°C/73°F, the temperature inside a vehicle can be extremely dangerous - more than 50°C/122°F
• reschedule or plan outdoor activities during cooler parts of the day
• before heading out, check the Air Quality Health Index website in your area, if available. Air pollution tends to be at higher levels during very hot days
• plan strenuous outdoor activities for cooler days, or choose a cooler location like a place with air conditioning or with tree shade

Find or bring shade to avoid being exposed to the sun

• tree-shaded areas can be as much as 5°C/9°F cooler than the surrounding area
• shade yourself by wearing a wide-brimmed, breathable hat, or using an umbrella
• wear sunglasses that have UVA and UVB protection
• use a sunscreen with sun protection factor (SPF) 15 or higher and follow the manufacturer's directions – do not use sunscreen on a child less than 6 months old

Check up on friends, family and/or neighbours regularly who may be at high risk during a heat event

Do not leave people or pets in parked vehicles as they can get very hot!

Contact your local public health unit for more information.

Useful Heat-Related Links:

• Health Canada
  • Acute Care During Extreme Heat
  • Community Care During Extreme Heat
  • Protect yourself from Extreme Heat
• Environment Canada
• Ministry of Environment and Climate Change – Air Quality Ontario
• Ministry of Labour