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Healthy Environments

Extreme Heat

Hot temperatures can be unsafe for our health and wellbeing. It can also harm community services we need, such as healthcare and the energy grid. Heat can affect everyone, but some people are at greater risk than others. Simcoe Muskoka is experiencing a rise in average summer temperatures and more very hot days due to climate change.

The good news is, we can prevent the negative health impacts of heat. To stay safe in hot weather, be aware of the risks and take precautions before heat happens. This will help protect you and your family. Simcoe Muskoka District Health Unit (SMDHU) monitors and shares information on heat-health impacts and offers information on ways to protect yourself from heat. We also work with partners to reduce the risks of heat in our communities. 

This page has information on how heat affects health, how to know if you are at risk, and tips to staying safe during hot weather.

If you are experiencing any of the symptoms listed below during a heat event, try to move to a cool place and drink liquids right away. Water is best.

Heat stroke is a medical emergency! If you are caring for someone who has a high body temperature and is either unconscious, confused, or has stopped sweating, call 911 or your local emergency number immediately.


Heat Health Impacts

Heat can harm health in different ways, including causing illness and death. Heat-related illnesses include dehydration, heat cramps, heat rash, heat edema (swelling of hands and feet), heat exhaustion, and heat stroke. Heat can make existing illnesses like lung and heart conditions worse, which could lead to serious illness or death. In addition, heat can increase risks for pregnant people and newborns. It can also affect mental health, causing mood and behavioural problems, worsening mental illness, and increasing increased aggression, violence, and suicide.

High temperatures and humidity can make it difficult for our body to control its temperature. This can cause heat stress when our internal temperature rises faster than it can cool off. Heat stress can harm important organs like the brain.

Some prescription medications and excessive drug and alcohol use can make it harder for the body to regulate temperature. If you have an existing health condition or are taking medications, it is important to talk to your healthcare provider or pharmacist to understand if you are at greater risk and follow their advice.

In hot weather, it's important to be aware of dehydration and heat illnesses like cramps, rashes, exhaustion, and stroke. These conditions can happen quickly so it's crucial to watch for signs and symptoms and check-in on how you and those around you feel. This can help prevent a medical emergency.

Take quick action to start cooling down if you or people you care for show signs of heat-related illness.

Watch for common symptoms of heat illness, including:

Mild to Moderate SymptomsSevere Symptoms

-  Headache

-  Nausea

-  Weakness, fatigue, or malaise

-  Irritability

-  Light-headed or dizziness

-  Disorientation

-  Extreme thirst

-  Skin rash

-  Muscle cramps

-  Decrease urination with unusually dark yellow urine

-  Increased heart rate

-  Skin feels very warm and sweaty

-  Body temperature over 38ºC

Mild or moderate heat illness can quickly become severe. Take action to cool down. If symptoms get worse or you are unsure, contact a healthcare provider. Call 811 or access digital care here.

-  Severe nausea or vomiting

-  Fainting or loss of consciousness

-  Confusion or disorientation

-  Difficulty speaking

-  Movement and coordination problems

-  Lethargic

-  Not sweating

-  Hot flushed skin or pale skin

-  Not urinating or very small amounts

-  Rapid breathing and/or heart rate

-  Body temperature over 39ºC

Seek help, call 911 immediately if you are caring for someone with severe symptoms. Severe heat illness and heat stroke are a medical emergency. While waiting for help to arrive, cool the person by:

-  Moving them to a cool place if possible

-  Removing excess clothing

-  Applying cold water to the skin

Health Canada provides further information on signs, symptoms, and safety tips during extreme heat.

Hot temperatures can change air, water, food quality and safety. Heat can increase rates of some diseases. Heat events stress our vital community services like healthcare and energy systems. 

Heat events can happen at the same time or close to other health hazards, such as wildfire smoke events or power outages. Understanding potential risks and creating a plan of action to reduce risks is important.

Who is at risk to the impacts of heat?

Heat affects everyone. However, some people are at higher risk. This is due to differences in people's exposure and sensitivity to heat and their ability to take protective measures.

Factors that may make a person at greater risk to heat include:

  • Older adults
  • Infants and children
  • Pregnant people
  • Pre-existing chronic diseases such as diabetes, heart disease, respiratory disease, or cancer
  • Mental illness such as schizophrenia, depression or anxiety, or cognitive impairment such as dementia
  • Reduced or impaired mobility
  • Use of certain medications (e.g., anticonvulsants, antidepressants, diuretics, immunosuppressants, interferons, anticoagulants)
  • Excess use of drugs or alcohol
  • Exercise in the heat
  • Occupational exposure to heat (including hot outdoor and indoor environments)
  • Living alone or are socially isolated
  • Experience of material deprivation (low socioeconomic status)
  • Experience of homelessness or marginal housing
  • Racialized people, newcomers to Canada, people who do not speak English or French
  • Exposure to Urban Heat Island

The more factors someone has, the higher the potential risk. Those without air conditioning and people with multiple risk factors, such as being an older adult and socially isolated, may be at higher risk for health problems. There are ways to prevent heat health impacts for all people.

You should check on your family, friends, and neighbours during hot and humid weather to make sure they're safe. This tool can help you do that. 

There are other things you can do to keep yourself and others safe, which are explained below.

Prevent Heat Health Impacts

There are things you can do before and during the heat to protect yourself and those you care about.

The best time to prepare for an extreme heat event is before it happens.

Understand the risks and make plans for what to do.

  • If you have a health condition or are taking medications, talk to your healthcare provider or pharmacist about your risks to heat. Follow their advice to stay safe.
  • Know the signs and symptoms of heat-health impacts and what to do if they occur. 
  • Identify if it is safe for you to stay home during periods of high heat. If you are at higher risk or your home gets very hot inside, plan to go somewhere else during extreme heat. Indoor temperatures of 31ºC or higher are dangerous. 
  • Know your home's cool spaces. Assess areas of your home that may stay cooler than others. 
  • Find cool spaces in your community you can access to stay cool. For example, a friend or family member's house with air conditioning, a library, community centres, a shopping centre, a movie theatre, religious centres, large parks with lots of tree coverage, and places with water features (public pool, beach, splash pad).
  • If you live alone or need extra help, identify a person who can check in on you during a heat event.
  • Make a plan for when hot, humid temperatures happen at the same time as other health threats like power outages, wildfire smoke, a severe storm. This resource can help you get prepared. 
  • Know what to do to stay safe and cool during extreme heat (see below).

Stay Informed

  • Know where to access more information or help.
    • -    Seek advice from a healthcare provider. If it is a medical emergency, call 911.
    • -    Additional resources can be identified in the resource section below.
  • Stay aware of weather forecasts and heat warnings.
    • -    Monitor weather forecasts and sign up to receive alerts with Environment Canada's WeatherCAN app. Download it now!
    • -    Pay attention to the media, Environment Canada, Simcoe Muskoka District Health Unit, and your local and regional governments for information about heat warnings and extreme heat events.

Be Prepared at Home

  • Make sure air conditioning, fans, and other cooling equipment are working.
  • If you do not have air conditioning, consider getting and installing a portable or window air conditioner.
  • Get a fan to help move cool air indoors in the evenings and mornings.
  • Install thermal curtains or window coverings to help block the sun.
  • Get a digital thermometer to measure indoor temperatures. Make sure to have extra batteries.
  • Prepare to use your home's cool spaces during extreme heat events (e.g., a basement).

Be Prepared at Work

  • If you work in the heat (outdoors or inside) or have a physically demanding job, work with your employer to develop a plan to stay safe in the heat.

There are ways to stay safe from the heat. Consider the following things to help you keep cool:

Protect Yourself

  • Drink lots of water, even if you don't feel thirsty.
  • Dress for the weather. Wear loose-fitted, light-coloured clothing, hats, and sunglasses. 
  • Use sunscreen with at least 30 SPF.
  • Reduce your activity level and avoid intense activity. Readjust your schedule to do activities in the cooler parts of the day.
  • Seek cool spaces. This can include air-conditioned spaces or shaded outdoor areas. Remember, indoor temperatures 31ºC can be dangerous.

Keep Cool

  • Take a cool shower or bath.
  • Make meals you do not need to cook in the oven.
  • Block the sun by closing blinds or curtains during the day.
  • Open windows at night to let cooler air into your home. Shut windows during the day to prevent hot air indoors.
  • If you have air conditioning, turn it on. Air conditioning does not need to be on at full blast to provide health benefits.
  • If you don't have air conditioning, use a fan. Only use fans in the evenings and early morning to circulate cool air from outside. Fans cannot effectively reduce body temperature or prevent heat-related illness. Do not rely on fans as your primary cooling method during extreme heat events.
  • Spend time in cool spaces in the community like shopping centres and libraries or seek cooler, breezier areas outdoors such as large parks with lots of trees and near water to spend time in and cool off.
  • If you live in a building or residence that gets very hot with inside temperatures of 31ºC or higher, plan to go elsewhere during extreme heat events.
  • Spent time in the coolest rooms of your home (e.g., sleep in the basement).

Stay Alert and Informed

  • Monitor for signs and symptoms of heat-related illness and other negative health outcomes.
  • Check temperature forecasts and heat warning alerts.
  • Seek trusted information about local responses and supports (e.g., news, municipal webpages, SMDHU webpage and social media).

Take Care of Others

  • Check on family, friends or neighbours, especially those at higher risk, to make sure they are staying cool and healthy and indoor temperatures are comfortable. Indoor temperatures above 31ºC are not safe. Use this resource to help you do an in-person health check. This resource is available in several languages.
  • Encourage those who may not know they are at higher risk to take steps to cool off (see below).
  • If you have air conditioning and higher-risk members of your family do not, invite them over.

Your voice is powerful! You can influence decision-makers at all levels of government by telling them that you want to see action to make our communities safer in heat events.

Consider these long-term strategies to reduce heat exposure for your home, apartment, or condo:

  • Green your home:
    • -    Plant deciduous trees in front of south and west facing windows.
    • -    If you live in an apartment or condo, add plants to your balcony and large leaf plants in light-facing windows.
  • Choose light-coloured reflective surfaces for outside the house, reduce impermeable surfaces.
  • Ventilation:
    • -    Learn to use windows and doors to naturally ventilate your unit.
    • -    When installing new windows, choose ones that open.
    • -    Get a portable or ceiling fan that increases air circulation.
    • -    Install a heat pump or air conditioner unit (even in one room).
  • Improve insulation:
    • -    Install blinds, heat-resistant curtains or reflective films that block the sun from hitting the windows.
    • -    Shade windows with outdoor shutters and awnings.
    • -    When installing new windows, choose ones with low solar heat grain coefficients that let less heat in.
  • Install temperature and humidity monitors or controls.
  • When possible, choose energy efficient lights and appliances that produce less 'waste' heat.

Check out these links for more information on cost-effective home heat protection strategies for your house or condo/apartment

There are funding programs to support these efforts. Some examples include:

Heat events are becoming more intense, severe, and longer-lasting due to climate change. An intense, extended extreme heat event is when daytime and nighttime temperatures get hotter every day and are well above seasonal norms for 3 or more days. Think of the 2021 heat event in British Columbia which occurred between June 25 and July 1 (8 days).

In addition to measures identified above, there are things you can do to prepare for an intense, extended extreme heat event.

Make plans for an extended extreme heat event. Consider:

  • Those at risk. Everyone can benefit from planning and preparing for an extended extreme heat event, but especially for those at greater risk. Seek or offer support to help others plan and prepare.
  • Assess if you can stay home. If you live somewhere that gets very hot, plan to go elsewhere during an extended extreme heat event. For people at risk to heat, risk increases at indoor temperatures of 26ºC and temperatures higher than 31ºC are dangerous. 
  • Assess your home's cool zones. Some spaces in your home may stay cooler than others. Use these spaces during an extended heat event (e.g., sleeping, day to day living). Focus your attention on keeping these spaces cool.
  • Identify other locations to get cool.
  • Identify an extreme heat buddy if you live alone. Your heat buddy can check in on you when it gets too hot or you can reach out to them for help.
  • Prepare your home. A few modifications can make a big difference during an extended extreme heat event.
    • -    Install a window air conditioner in at least one room.
    • -    Install thermal curtains or window coverings.
    • -    Keep a digital thermometer available to read indoor temperatures.
    • -    Have a fan available to move cooler air indoors during the late evening and early mornings.
    • -    Install a heat pump.
    • -    Install exterior covers or have materials on hand to make temporary window reflectors. Reflective films can block the sun from hitting the windows. This can be simple like putting cardboard on the outside of the window.
  • Have an emergency kit available.
  • Activate your plan to stay cool when temperatures rise.

It is very possible that a heat event overlaps with other health threats. It is important to plan and be prepared for events that can happen at the same time.

Power Outages

During a heat event, severe weather or high demand for electricity can result in a power outage. This may affect access to air conditioning or fans. Take the following steps to prepare and cope with a power outage during a heat event.

  • Take steps to keep cool air in and hot air out. This can include simple things like keeping windows covered with blinds or curtains, outdoor shutters, awnings, weather-strip doors and windows.
  • Have an emergency kit available that includes food, water, and a battery-operated radio and flashlight.
  • Take steps to stay safe and cool identified above.
  • Remember, for people at risk to heat, risk increases at indoor temperatures at 26ºC and temperatures higher than 31ºC are dangerous. If your home becomes too hot, seek cooler spaces including those in your community, or outside areas with lots of shade and near water if possible.

Poor Air Quality

Hot and humid air can bring deteriorating air quality and can result in the Air Quality Health Index approaching the moderate to high-risk category. Extreme heat can also lead to higher risk of wildfires. Check the Air Quality Health Index to help you make decisions about your health. Take steps to prepare for the heat and stay safe and cool as identified above.

If indoor temperatures are comfortable, keep windows and doors closed. For most people, exposure to heat is a bigger risk to health than exposure to wildfire smoke. If you cannot get cool inside, seek cooler spaces in your community or go outside, even if there is wildfire smoke. This is safer than staying in indoor environments that are too hot.

Extreme Heat Alerts

SMDHU alerts the community of extreme heat events that can be harmful to health. This is part of a province-wide system that uses evidence-based triggers to issue a heat warning or extended heat warning. Heat warnings are issued when:

Level Criteria Duration
Heat Warning Temperatures are expected to be at least 31ºC and overnight temperatures are at least 20ºC
Humidex is at least 40ºC
2 days
Extended Heat Warning Temperatures are expected to be at least 31ºC and overnight temperatures are at least 20ºC
Humidex is at least 40ºC
3 or more days 

When a heat warning is issued, SMDHU boosts communication with the public and works with the community to promote actions that protect health. SMDHU monitors heat events Monday to Friday between 8:30 AM and 4:30 PM.

Check Environment and Climate Change Canada's website or mobile app (WeatherCAN) for information on your local forecast and weather alerts.

Climate Health Connection

Climate change harms the health and wellbeing of people in Simcoe Muskoka. The average temperature is getting warmer. Extreme heat events (heat waves) are becoming more common, severe, and longer-lasting. This might sound good in the middle of a cold winter, but it harms our health and communities. Climate change can also make cold events worse.

This webpage shares how extreme heat can be dangerous to health. Rising temperatures can also influence health related to air, water and food quality, infectious diseases, extreme weather, and extreme temperatures (including extreme cold events).

In addition to actions that can help keep you safe from the extreme heat highlighted above, other climate mitigation and adaptation actions can help prevent harm from extreme heat and other climate-related problems in the short and long term. Climate action protects and promotes health and wellbeing but can also provide economic savings.

Everyone can take action against climate change. Examples include efforts to conserve energy, reduce consumption, recycle, planting trees. We can also support large-scale changes by staying informed, getting involved, and speaking out.

SMDHU works with our partners to increase community resilience and reduce the adverse health outcomes of climate change and extreme heat. We collaborate with municipal and community partners to inform healthy community design and climate action. We implement heat warning and information systems, conduct surveillance, increase awareness, and encourage protective measures to ensure that our community is safe and prepared for the impact of climate change.


Information on Weather Forecast and Alerts

Environment and Climate Change Canada:

Most places you get your weather forecast.

Follow SMDHU on Instagram, Facebook, or Twitter to receive communications on extreme heat and other health risks.

Extreme Heat and Health Resources

Health Canada:

Government of Ontario:

Climate Change and Heat:

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