Temperatures to ease as week ends, but will jump again on Saturday
This article was written by Daniel Opasinis and was published in the Toronto Star on August 14, 2025.
A heat warning for most of southern Ontario, including Toronto, has finally ended with a wave of cooler air set to bring some relief.
Environment Canada says a less humid air mass is expected to move through the province on the heels of the multiday heat wave.
The cooler forecast also comes as wildfires burn in parts of the province, notably in the region around Kawartha Lakes, which reported one of blazes its battling grew rapidly from five to 33.5 hectares Tuesday.
Thursday marks the first day without a heat warning, bringing a forecast for a daytime high of 27 C, feeling more like 33 with humidity, and a UV index of 8. Expect clear skies and a low of 19 C in the evening.
On Friday, expect a sunny 27 C with a night time low of 22 C.
However, temperatures are expected to spike again.
“It’s definitely possible we could be back in the warning this weekend. It might even be confined to just sort of the urban area of southern Ontario,” said Environment Canada meteorologist Crawford Luke.
The heat will continue into Saturday, with a sunny daytime high of 29 C. But a 40 per cent chance of showers and a 20 C evening low could deter the risk of a repeated heat event.
After Saturday, more comfortable temperatures are on the horizon.
Daytime highs are expected to plummet Sunday, with 27 C forecast along with an evening low of 16 C.
A 40 per cent chance of rain will carry into Sunday, as well. Luke said this is the day that will make or break a heat warning in the GTA, as any delay in Sunday’s expected cold front could create conditions considered a heat event.
Next week will start with a mix of sun and cloud and a high of 22 C with a nighttime low of 17 C on Monday.
So far, Tuesday’s forecast calls for a high of 23 C, continuing the trend of more comfortable weather days in the GTA.
What about air quality?
Wildfires across Canada have kept air quality in a state of limbo in the GTA. However, a decrease in humidity across Ontario could bring improvements.
IQAir forecasts Toronto’s air quality to hover between “good” and “moderate” levels throughout the week.
Luke said smoke from the Kawartha Lakes fires is unlikely to reach Toronto, but a change in wind direction could always send more smoke our way from larger fires in Manitoba and northern Ontario.
“We might notice a bit of haze or smoke tonight, tomorrow, but it should not be anything severe, like we’ve seen at other points this summer,” he said.
Not only can a decrease in smoke increase air quality, but a break from this summer’s back to back heat events could provide relief to many people who experience heatrelated health struggles.
“Take action to protect yourself and others — extreme heat can affect everyone’s health. Determine if you or others around you are at greater risk of heat illness. Check on older adults, those living alone and other atrisk people inperson or on the phone multiple times a day,” Environment Canada’s heat warning stated.
This article was written by Anakana Schofield and was published in the Toronto Star on August 13, 2025.
It is a melancholy object and mighty affront for those who must suffer the suffocation of a heat wave, which currently is most people in Canada and increasingly every single person on planet Earth.
I think it is agreed that, like our longsuffering friends the lobsters, we are all going to boil together but the question is: How can we comfort each other inside life’s bubbling pan?
Once there might have existed those who come to life in the heat, those who rejoice at the mere sight of the sun and those, like me, who manage to get heatstroke and seconddegree sunburns while staying inside, with the curtains closed and the lights turned off. Yet when polling the plain people of the internet this week, I found no one who likes heatwaves.
During a recent stretch in Vancouver, I called my local, heat expert bestie Mome Gul, who was born in Pakistan, raised in Saudi Arabia — she was cooking! On a hot stove! “I love it. I come to life in the heat,” she said between loud sizzles of onion. “I am dying,” I told her. “Something is very wrong with me. My head is leaving my body.”
“I like the temperature to be 25 to 30 C. I feel alive. I think I like heat because I have cheated heat. I lived in Saudi Arabia, which has air conditioning and electricity is heavily subsidized. Put on long flowing, cotton clothes,” she advised. “People make the mistake of thinking the less clothes you wear the cooler you’ll be. Not true.”
Even my son was perplexed, as I staggered about warning him, I might throw up … until I did throw up. “What’s wrong with you, Mammy? You are turning into a physical wreck!” This discombobulation carried on as long it remained above 25 C. If I tried to exit my apartment I couldn’t make it to the end of the block, without feeling my legs give way. If I made it to the supermarket, I had to hold on to the fixtures as if I was on a rushhour bus. My brain could not even form words properly and I wasn’t sure where I was until I stuck my two Hobbity arms into the meat cooler like a zombie and managed to cool down a degree or two.
Finally, since it takes a village to defeat me, a large fuzzy bumble bee entered my shoe and stung me on the toe. I felt like my foot had been amputated with a hot axe, so I laid down and did nothing but eat emergency cherries for 36 hours.
A week later, my GP (gasp! — that rare and highly endangered species) took my blood pressure. I was surprised to learn I have the blood pressure of a six-to-eight-yea-rold child rather than Pompey the Great. On the upside, I could now eat salt and vinegar chips, drink electrolytes and put my legs up in the air. Obviously, a salty novelist is precisely the person to come up with the necessary interventions needed to deliver us to September alive.
And so I laid with my legs up and thought: short of inventing a time machine to excise the hottest hours of the day, I see no path forward for those of us with small veins, bad tempers and hot flashes who do very poorly in the heat. Yet we must do something. Forest fires are raging and workers must fight them. Dishwashers are trapped in local kitchens with no air conditioning. Construction workers are dissolving high above us. Food delivery cyclists are bringing the airconditioned their supper. The poor and our most vulnerable disproportionately die from this heat. Even supplying air conditioners lands them with bills they cannot pay.
Still, my modest proposal for this extended festival of scorching is we should take inspiration from our ursine friends Yogi Bear or Hank the Tank and do an inverse hibernation between July and October.
If this fails: keep an eye on elderlies, the swaying and the bad tempered during these trying times. Offer to shop for them, wave fans on them or buy them air conditioners, and — vitally — give up your seat on transit.
The heat was so bad here recently even my son was feeling weird by the end of the day. If only I could take him to a 24hour library, or an allnight swimming pool. I could just feed him frozen grapes. Maybe that will help.
Keep an eye on elderlies, the swaying and the bad tempered during these trying times. Offer to shop for them, wave fans on them or buy them air conditioners, and — vitally — give up your seat on transit
This article was written by Daniel Opasinis and was published in the Toronto Star on August 13, 2025.
Some relief from the latest blistering heat wave is expected as Environment Canada forecasts the arrival of a cooler air mass.
The weather agency anticipated the slightly cooler air to arrive Tuesday night, but also warned the GTA and eastern Ontario may continue to sizzle in hot and humid conditions into Wednesday.
Environment Canada announced the multiday heat alert on Saturday, warning that temperatures could feel like up to 42 C with humidity.
A 70 per cent chance of precipitation is expected for Wednesday, with a risk of thunderstorms in late morning and afternoon. A high of 28 C will feel like 37 C with the humidex. Wednesday night could see more showers and a possible thunderstorms before skies are expected to clear through the evening. The nighttime temperature is forecast to drop to 21 C.
On Thursday, temperatures are expected to climb back up to 28 C under sunny skies. That will be followed by a clear night with a low of 19 C.
More sun is expected Friday with a high of 27 C and a low of 21 C.
Saturday’s forecast calls for more sunshine and a high of 29 C. There’s a 20 per cent chance of showers at night as some clouds roll back in. The evening will also bring a low of 23 C.
Sunday is forecast to be partly overcast with a 40 per cent chance of showers and a high of 28 C, followed by a cloudy night with a low of 18 C.
Environment Canada offers tips to avoid heatrelated health risks in the city, and warns about deteriorating air quality amid the humidity.
“Check on older adults, those living alone and other atrisk people inperson or on the phone multiple times a day,” the heat warning reads.
The weather agency shared that symptoms of heat stroke and heat exhaustion — headache, nausea, dizziness, thirst, dark urine and intense fatigue — should be closely monitored.
Tips to protect yourself in the intense heat include drinking water before you feel thirsty; limit direct exposure to the sun and try to schedule outdoor activities during the cooler parts of the day; and never leave people — especially young children — and pets inside a parked vehicle.
Kids find a spot to cool off as heat wave settles on southern Ontario
This article was written by Allie Moustakis and was published in the Toronto Star on July 29, 2025.
The Environment Canada heat warning is here to stay, Toronto.
After a sizzling weekend, temperatures held steady near the mid30s Monday, with humidity making it feel significantly hotter. Environment Canada said the humidex hit 41 by the afternoon, and overnight lows of 22 C offered little relief from the sticky conditions.
Cooler temperatures are expected to arrive on Wednesday, bringing an end to the multiday heat event.
The heat warning covers all parts of southern Ontario, stretching from along Lake Erie and Lake Ontario in the west all the way to Cornwall in the east.
A previous heat warning was also issued for Toronto and other parts of the province last Thursday, when temperatures hit the mid30s and similar humidex values in the 40s. The current warning is expected to remain in place through Tuesday.
Dozens of Toronto residents were walking on shaded sidewalks, enjoying lunch on patios and sitting on public wooden benches along Lake Ontario on Monday afternoon.
The sun will be out again on Tuesday when temperatures are expected to hit a daytime high of 30 C. The humidex will sit at 38 C with a UV of nine again. Clouds will roll in at night, bringing with them a 40 per cent chance of showers and a low of 21 C.
With the heat warning expected to be over by Wednesday, the city will see a high of 28 C, a 30 per cent chance of showers and some clouds overhead. The night will be cool and cloudy with a low of 20 C.
By Thursday, temperatures will reach a high of 25 C and a low of 17 C with sunny and clear skies in the day and night. Friday will be sunny with a daytime high of 25 C. Skies will remain clear at night and overnight lows will drop to 11 C.
Temperatures will stay relatively similar over the weekend.
Environment Canada continues to advise caution during extreme heat events, especially for older adults, people with preexisting health conditions and those who are at greater risk.
To help residents beat the heat, several outdoor pools in the city will remain open late, with extended hours at Alex Duff, Fairbank, McGregor Park, Monarch Park, North Toronto, Smithfield and Sunnyside until 11:45 p.m. Halbert Park pool will also stay open until 9 p.m.
High temperatures, humidity expected to last to Tuesday
This article was written by Elissa Mendes and was published in the Toronto Star on July 28, 2025.
Things are sizzling once again in Toronto, as the city is back under an Environment Canada heat warning.
The heat warning is expected to last through Tuesday, Environment Canada said, adding there’s “some uncertainty” about how long it’ll last in other parts of the province.
Central Ontario could emerge from the heat warning Monday night, the agency said, while it could last into Wednesday in other areas.
What’s the Environment Canada forecast for Toronto?
Monday will be sunny as fog patches disappear in the morning, with a high of 33 C feeling like 40 with humidity. The UV index will rise to 9 again. At night, expect a 30 per cent chance of showers with a low of 22 C.
Tuesday — expected to be the tail end of the heat warning — will be partially overcast with a 40 per cent chance of showers and a high of 31 C. Tuesday night will see a 40 per cent chance of showers as temperatures dip to 21 C.
With the heat warning expected to be over by Wednesday, Toronto will see a high of 30 C, a 30 per cent chance of showers and some clouds overhead. Wednesday night will be cool and clear with a low of 17 C.
Thursday will see sunshine and a high of 26 C, cooling to 15 C at night.
Friday will be more of the same with a sunny daytime high of 25 C and nighttime low of 15 C.
Heading into the weekend, Saturday will see blue skies and a high of 26 C.
What are the symptoms to watch out for?
Watch out for early signs of heat exhaustion, Environment Canada urged, which include headache, nausea, dizziness, thirst, dark urine and intense fatigue. If you suspect heat exhaustion, stop your activity and drink water, the agency said.
Heat stroke, however, is a medical emergency, the agency said. Signs of heat stroke include red and hot skin, dizziness, nausea, confusion and a change in consciousness. If a person might have heat stroke, call for emergency medical attention and try to cool them down.
Extreme heat events mean you should check on older adults, people who live alone and other atrisk people inperson or over the phone multiple times per day, Environment Canada said.
How can I keep cool and stay safe?
Environment Canada urged people to drink water often — and before you feel thirsty. You should also close your blinds or shades and open your windows if it’s cooler outside than it is inside.
You should also turn on air conditioning, use a fan or move to a cooler area of your home, Environment Canada added.
If you want to take part in activities, schedule them for the coolest part of the day, Environment Canada said, encouraging people to limit direct sun exposure and to wear light, loosefitting clothing with a widebrimmed hat.
Anyone looking for free ways to cool down can also use the city’s interactive map of community centres, pools, libraries and other heat relief spaces.
This article was written by Anastasia Blosser and Elissa Mendes, and was published in the Toronto Star on July 24, 2025.
It was nice while it lasted.
After nearly a week of temperatures in the low to high 20s, more hot and humid weather is on Toronto’s horizon, according to Environment Canada, which has issued another heat warning for the city.
The weather agency said temperatures will be the hottest Thursday, when the heat event is expected to kick off.
“While daytime high temperatures will not be as extreme on Friday and into the weekend, night time lows are expected to remain warm throughout,” Environment Canada added in its warning.
Temperatures are expected to hover around the high 20s to low 30s but the humidity could make it feel as hot as 44, according to the heat warning. There will also be onandoff rain throughout the next week, the local forecast says.
It has already been shaping up to be a hot summer for the city with there already being multiple stretches of heat warnings over the past month.
The sun will stick around on Thursday with a high of 34 C, which could feel like 42 because of the humidity. At night, clouds will roll in, bringing a 40 per cent chance of showers with them. The low will be 24 C.
Friday will also be cloudy with a 60 per cent chance of showers and high of 29 C. Skies will remain cloudy at night and temperatures will drop to a low of 20 C.
Kicking off the weekend, skies will begin to clear on Saturday with a high of 28 C and low of 18 C.
Sunday will bring a mix of sun and cloud with 30 per cent chance of showers and cloudy periods in the evening. There will be a high of 28 C and a low of 19 C.
Monday will be similar, with a mix of sun and cloud and a high of 30 C. Later in the day, there will be cloudy periods and a low of 20 C.
Tuesday will be cloudy with a 30 per cent chance of showers and high of 28 C.
As temperatures climb, Environment Canada is urging people to drink water often — and before you feel thirsty.
As well, you should plan outdoor activities for the coolest parts of the day, limit direct sun and heat exposure and wear light and loose clothing with a widebrimmed hate.
Open your windows if it’s cooler outside than indoors, but otherwise, keep your blinds and shades closed, the agency said. You should also turn on air conditioning or a fan, or move to a cooler part of your home.
Also, watch out for signs of heat exhaustion, which might include a headache, nausea, dizziness, thirst, dark urine and intense fatigue. People who suspect heat exhaustion should stop activities and drink water, the agency said.
On the other hand, heat stroke is a medical emergency, with signs including red and hot skin, dizziness, nausea, confusion and a change in consciousness. If you see signs of heat stroke, call for emergency medical attention and try to cool the person down.
Torontonians can also use the city’s interactive cool spaces map to find public pools, community centres and other free spots to beat the July heat.
This article was written by Allie Moustakis and was published in the Toronto Star on July 5, 2025.
Toronto is moving back into the heat (and humidity) this weekend.
The second heat warning of the summer was issued Friday for the Greater Toronto Area and much of the province as humidex values are expected to exceed 40 later this weekend.
Temperatures are expected to climb up to the low 30s on Saturday and Sunday, feeling hotter with the humidity.
Environment Canada said the heat warning will be in effect for much of Saturday and last until Sunday night.
Don’t let the clouds fool you. Saturday will be sticky, hitting a daytime high of 31 C, which will feel closer to 41 with the humidity. Winds will gust to 20 km/h and there’s a 30 per cent chance of showers plus a risk of thunderstorm heading into the afternoon. The UV index is expected to be high, reaching past nine, before temperatures drop to a low of 23 C at night.
Sunday will be similar with a mix of sun and cloud, a 30 per cent chance of showers and a high of 33 C. Chances of rain will jump to 40 per cent at night with a low of 20 C.
The beginning of next week is expected to see slightly cooler temperatures — with a 28 C daytime high on Monday and 27 C high on Tuesday.
Humidity can make temperatures feel warmer, trapping moisture on your body and making it difficult to dry off after sweating, according to Environment Canada, who urge people to avoid exerting themselves and head for cooler temperatures when they overheat.
Toronto offers an interactive cool spaces map, but people can also protect themselves by taking a cool shower, using a fan, drinking extra water and avoiding alcoholic, caffeinated and sugary beverages, an expert previously told the Star.
This article was written by Dean Flannery and was published in the Toronto Star on June 25, 2025.
It’s been hot in Ontario, and dangerously so. For the past few days, my phone has been blasting out regular health warnings about the extreme temperatures.
Not that I’ve needed the reminder. Opening my front door this week has been like opening the oven door when the broiler is running. On Monday, temperatures hovered between 33 and 36 C. With the humidex, it felt as hot as 46 C at times, the kind of heat that can make you feel ill fast if you don’t take steps to cool yourself — assuming you have the means to do so.
But what about those who depend on others to keep their environment healthy?
That’s the situation for students across Ontario, where heat waves can occur even in spring and fall and most public schools lack air conditioning. This week, thousands of kids are spending their last week of school in spaces that are uncomfortably hot and offer limited opportunities for cooling.
In Toronto, only 30 per cent of public schools have central air conditioning. In Hamilton, it’s 50 per cent — and the more than $50 million it would take to fix that state of affairs is beyond the school board’s budget.
Yet instead of investing in cooling infrastructure, Premier Doug Ford’s government has taken to blaming school boards for excessive classroom heat. Meanwhile, kids are left with a patchwork of protocols to help them cope, which can include being kept indoors and cycled in and out of designated cooling spaces such as libraries and gyms.
So just how hot is too hot for classrooms? Some school boards give administrators the option to cut the day short if outdoor temperatures reach the high 40s — but even the Toronto District School Board acknowledged this week that it was unlikely to do so, because of the burden on parents.
As kids can’t simply leave class and call it a day, they have to endure real harms to their wellbeing, not to mention their ability to learn and write exams. You may be inclined to shrug off these harms, given the limited duration of heat waves. But you’d also be shrugging off the province’s obligation to provide students with fundamentally safe learning spaces all year long, not just when the cost of doing so is convenient.
There’s also the fact that schools are workplaces, where putting teachers in the position of having to deal with naturally distressed kids and inadequate options for relief is not only an unjustifiable occupational burden but also a gendered one: 76 per cent of teachers in Ontario are women.
The need for investment is urgent, and it’s not going away. Kids today are dealing with heat events that are more frequent and more intense than what their parents or grandparents dealt with. In an April 2025 report on the need for better cooling in childcare spaces, the Canadian Environmental Law Association estimates that a 10yearold in 2024 would’ve experienced 36 times more heat waves than a 10yearold in 1970.
In recognition of this increased exposure, CELA and the Canadian Partnership for Children’s Health and Environment are calling on the federal and provincial governments to create a comprehensive plan to address the need for investment in healthier, more climateresilient schools and childcare spaces.
These calls for leadership rather than excuses come at an opportune time. Queen’s Park and Ottawa, so often engaged in stultifying jurisdictional battles, have been uncharacteristically aligned in their desire to fasttrack infrastructure projects. In an era of sweeping power moves, they’d be wise to apply some of this energy to cleaning up the lingering messes that have been exacerbated by chronic underfunding of our social infrastructure.
Building climate resilience in schools starts with establishing a legal maximum for indoor temperatures. CELA and CPCHE want Ontario to amend the Education Act or pass regulations to set the threshold at 26 C in both schools and childcare spaces, and they want it to offer dedicated infrastructure funding to make this a practical reality. Far from arbitrary, the proposed threshold is based on BC Centre for Disease Control analysis of the heat dome that struck British Columbia in 2021, killing hundreds.
Amid a rapidly warming climate, air conditioning in schools can no longer be considered a luxury. It’s an essential public health intervention — one that Ontario politicians enjoy in their workplaces and that kids deserve, too.
This article was written by Dr. Shazma Mithani and was published in the Globe & Mail on June 24, 2025.
Few people expect to end up in the emergency department because of hot weather, but heat-related illness sends many people to the hospital every year.
During the summer months, I frequently see patients suffering from heat exhaustion and dehydration. Many who come in are surprised at how quickly their symptoms develop after feeling well spending time outdoors for hours. In more serious cases, patients arrive dangerously close to heat stroke – a life-threatening condition requiring immediate medical attention.
According to data from the Canadian Hospitals Injury Reporting and Prevention Program, extreme heat events are contributing to a rise in emergency visits, particularly among vulnerable populations. And the Canadian Medical Association has said: “Illness from extreme heat waves places extra demands on a system already strained by a lack of primary care access and record ER wait times.”
As temperatures rise this summer, here are some things to know about heat-related illness and how to lower your risk.
HEAT STROKE IS MORE THAN JUST ‘OVERHEATING’
Heat-related illness happens when the body can’t regulate its temperature properly. Although mild overheating might seem like no big deal, progression of this overheating, while failing to cool down, can lead to serious health complications.
The term heat stroke is often misused to describe much milder heat-related illness. If you’ve ever overheated or felt drained after a hot day, this is almost certainly not heat stroke. True heat stroke is a medical emergency characterized by confusion, loss of consciousness and a dangerously high body temperature. It requires emergency department care and rapid treatment; failing to recognize it can be fatal.
HOW TO SPOT THE WARNING SIGNS
Heat-related illness exists on a spectrum, so recognizing early symptoms is key to avoiding progression:
Heat rash: A red, raised rash in areas of sweat production (armpits, elbow creases, knee creases and neck) that typically occurs several hours after heat exposure. The rash is usually itchy and takes a few days to resolve.
Heat cramps: Painful muscle spasms, usually in the legs or abdomen. Heat cramps can occur during exertion in hot conditions owing to a disproportionate loss of electrolytes compared with water (in sweat). They are easily treated with hydration, electrolytes and rest.
Fainting: Heat can cause the blood vessels in the body to dilate and decrease blood pressure. This drop in blood pressure can lead to fainting episodes (or heat syncope) that are managed with hydration, electrolytes and removal from heat.
Heat exhaustion: This consists of heavy sweating, dizziness, nausea/vomiting, headache and a fast heartbeat. It often occurs with prolonged or vigorous exertion in hot conditions. Without intervention, this can escalate to heat stroke. If any of these symptoms occur, it’s important to immediately get to a cool environment, and replace fluids and electrolytes. If symptoms don’t improve rapidly, this means progression to heat stroke is likely and the patient needs to go to the hospital emergency department immediately.
Heat stroke: This is a medical emergency that is the progression of heat exhaustion. It consists of severe confusion, loss of consciousness or even seizures. The skin is typically hot and dry (with no sweating). This is a true medical emergency: Call 911 immediately.
WHEN TO SEEK MEDICAL CARE
While mild symptoms can often be managed with cooling strategies, some situations require urgent medical care:
Dizziness, nausea or weakness that persists after rest and hydration.
Any signs of heat stroke as outlined above.
Individuals with underlying conditions such as heart disease, high blood pressure, diabetes and kidney disease who have prolonged symptoms of heat illness.
WHO IS MOST AT RISK?
Some groups are more vulnerable to heat-related illness owing to their body’s inability to regulate temperature effectively or other factors such as socio-economic conditions. These include:
Older adults: Aging affects the body’s ability to cool down efficiently.
Infants and young children: Kids lose body fluids more quickly and may not be able to express discomfort from the heat clearly.
People with chronic medical conditions: Underlying health conditions such as heart disease, diabetes or respiratory illnesses make temperature regulation more challenging.
Outdoor workers and athletes: Exposure to extreme temperatures for long periods without adequate hydration or cooling breaks leads to increased risk.
Certain medications: Medications such as diuretics, betablockers and antihistamines can impair heat tolerance.
Unstably housed: Lack of access to air-conditioned spaces and exposure to extreme heat can increase risk.
PREVENT HEAT ILLNESS BY STAYING COOL AND MONITORING FOR SYMPTOMS
The most important factors in avoiding heat illness start with awareness, preparation and recognizing symptoms early to help keep yourself and your loved ones safe.
Hydrate, hydrate, hydrate: Drink plenty of water and don’t wait until you’re thirsty. Electrolyte-rich drinks (such as Pedialyte, Skratch Labs drink mix, low-sugar Gatorade or Powerade, or equivalent drinks) can help replace lost salt in sweat during extreme heat or exertion in the heat. Avoid caffeine (including energy drinks) and alcohol as much as possible, since both can lead to dehydration.
Dress appropriately: Lightweight, light-coloured and loose clothing helps your body regulate heat better. Hats and sunglasses also provide protection.
Limit time outside during peak hours and stay cool: The hottest hours (10 a.m. to 4 p.m.) are when heat exposure is most dangerous. Limit outdoor activities, especially exertion and exercise, during this time. When you are outside, take regular breaks indoors (ideally in airconditioned spaces) or in the shade if you can’t get indoors. While outside, consider cool misting and cool compresses to help decrease body temperature.
Pay attention to symptoms: Feeling lightheaded or nauseous? Stop what you’re doing, move to a cool place and rehydrate. Ignoring the early symptoms of heat exhaustion can quickly turn dangerous.
Dr. Shazma Mithani is an emergency physician working with adult and pediatric patients in Edmonton. Mithani is actively involved with the Canadian Medical Association, Alberta Medical Association and Sexual Assault Centre of Edmonton. She is also co-host of The Doc Talk Podcast.
Ask a Doctor is a series of physician-authored columns offering insights and advice on common health topics.
Doctors share tips to stay cool as city faces high temperatures and humidity
This article was written by Kevin Jiang and was published in the Toronto Star on June 19, 2025.
It was the height of an exceptionally humid heat wave last July when an elderly patient was rushed to the emergency room with what looked like a heart attack.
Pain coursed through their chest and they could hardly breathe, said Dr. Edward Xie, the emergency physician who treated the patient. It was the end result of several days spent mired in extreme heat and humidity.
“They needed to be admitted to the hospital for basically the equivalent of a heart attack,” Xie, who is also an associate professor at the University of Toronto, said. “It was a lot of strain on the heart. Their body was basically shutting down because it couldn’t keep up with cooling itself.”
Like many Torontonians, this elderly patient lived in an apartment without air conditioning, Xie said. With no way to escape the oppressive heat and humidity, they were left to grow “sicker and sicker” over the course of several days — made worse by their preexisting heart and lung conditions.
“I basically have the same story every year,” he continued. “On very hot days, this is the most common presentation of people who don’t have heat pumps or air conditioning.”
Like clockwork, a stream of patients present to the emergency room whenever the thermostat breaches 30 C, especially when it’s humid out, Xie said. Studies suggest an average of 120 people die of heatrelated incidents every year in Toronto — and the danger only escalates the more humid it gets, experts say.
Our bodies have two main methods of cooling down when it’s hot out.
We wet our skin with sweat, dissipating heat when the perspiration evaporates. At the same time, our hearts beat faster and our blood vessels just under the skin dilate, sending hot blood coursing toward our skin and outer extremities where it can cool off, explained Dr. Samantha Green, a family physician and expert on the health consequences of climate change.
Humidity throws both those mechanisms out of whack.
It becomes far more difficult for sweat to evaporate when the air is already filled with moisture, Green said. With its ability to cool down diminished, our bodies heat up quicker, raising our risk of heat stroke.
“As humidity increases, the effectiveness of sweating decreases. And at around 90 per cent humidity, (sweating becomes) ineffective,” Green said.
This comes with another problem. Our bodies sweat more when it’s humid out, to compensate for the reduction in efficiency, Xie said.
Excess sweating can also damage our kidneys, which require us to be properly hydrated to function properly.
Elsewhere, our hearts are straining harder than usual to pump blood toward the skin and extremities to make up for our dwindling ability to cool ourselves, Green said.
There’s a complicated method of measuring temperature while taking into account humidity — as well as wind and solar radiation — called wet bulb globe temperature.
It’s generally believed a wet bulb reading greater than 35 C is the upper limit for human survivability, said Peter Crank, an assistant professor of geography and environmental management at the University of Waterloo.
“At that point, the environment around you is essentially so warm and so humid in combination, that your body is no longer able to maintain thermal regulation,” he said.
For reference, Wednesday, when temperatures climbed above 28 C with a relative humidity above 80 per cent, had a wet bulb of around 20 C, according to weather forecasting tool Meteologix.
The people at greatest risk of high heat and humidity include the elderly; people with chronic heart, lung and kidney conditions; people who work outdoors; and people without air conditioning, the experts say.
These individuals must take extra care to cool down, Green said. If possible, she advises finding a cool space near you and visiting regularly — the City of Toronto has an interactive map of cool spaces on its website. “If that’s not possible, stay cool by taking a cool shower,” she said. If your home has no air conditioning, consider installing window covers to block out the sun during the day and keep your windows open during the night, she said.
A fan can help as well, so long as the indoor air temperature remains below 35 C.
It’s important to drink extra water when it’s hot out, Xie said. Just avoid alcoholic, caffeinated or sugary beverages, as these can dehydrate you further.
You may also consider applying an ice pack to areas of the body with more blood supply, such as the back of the neck, under the armpits or near the groin, Green added.
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