Toronto to see heat wave with 'extremely hot' conditions: What are the risks?

This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis or treatment. Contact a qualified medical professional before engaging in any physical activity, or making any changes to your diet, medication or lifestyle.

As temperatures continue to rise in parts of Canada, a family physician says people should be aware heat is the deadliest of the extreme weather events.

Knowing how to stay safe is important.

"Extreme heat can cause direct heat-related illness, so it can cause heat exhaustion or the more serious — a heat stroke," said Samantha Green, a family physician at Unity Health Toronto, who added that a heat stroke has a 50 per cent mortality rate.

Environment Canada sent out a heat warning for Toronto on July 26, noting that temperatures are expected to reach 30 degrees Celsius on Wednesday.

The heat and humidity is expected to continue through the week, with slightly cooler temperatures but humidex values in the upper thirties on Thursday. On Friday, the humidex values are expected to reach 40 in many areas. By the weekend, cooler conditions are expected.

"Drink plenty of water even before you feel thirsty and stay in a cool place," Environment Canada added. "Check on older family, friends and neighbours. Make sure they are cool and drinking water. Never leave people or pets inside a parked vehicle."

According to the World Meteorological Organization, June saw the warmest global average temperature on record, which continued into July.

"The extreme weather – an increasingly frequent occurrence in our warming climate – is having a major impact on human health, ecosystems, economies, agriculture, energy and water supplies," said WMO Secretary-General Prof. Petteri Taalas in the blog post.

What does extreme heat do to our bodies?

According to the government of Canada, common symptoms of hot weather illnesses include heat cramps, heat exhaustion and a heat stroke.

Heat cramps are described as "having sharp pains in the muscles caused by salt imbalance resulting from the failure to replace salt lost with excessive sweat."

Heat exhaustion symptoms include "heavy sweating, weakness, dizziness, headache, diarrhea, muscle cramps, cold and clammy skin, low blood pressure, disorientation and possible vomiting," it said. "These are caused by excessive loss of water and salt."

Heat stroke includes "a core body temperature greater than 40ºC, complete or partial loss of consciousness, reduced cognitive function and cessation of sweating (hot and dry skin), dilated pupils and elevated blood pressure. Skin may be flushed at first, later ashen or purplish," it claimed.

Green explained not only can heat cause heat exhaustion or a serious heat stroke, but it can also exacerbate underlying health conditions, like heart and lung disease and mental illness.

"An increase in temperature has been correlated with an increase in depression symptoms," she added.

Heat can also cause symptoms of anxiety, an increase in violence and an increase in suicide tendencies.

Why do our bodies react that way to extreme heat?

Green explained the human body has an internal temperature regulation system. Essentially, the brain "acts as a thermostat."

The skin also acts as a coolant through perspiration or sweating.

"That system can be overwhelmed when the temperature and humidity exceed a threshold, a particular threshold. So when our body temperature exceeds 37.5 degrees, that is called hyperthermia," Green said.

She said at first, it's "compensatory hyperthermia" where our body reacts by increasing the heart rate, sweating and breathing faster to keep the air.

"That is in an attempt to cool our bodies down," said Green. "But when the body temperature exceeds 40 degrees, it's just too much. So, our bodies are incapable of the mechanisms that we normally have."

What are the treatments for heat-related illnesses?

When it comes to treating heat exhaustion, cramps or stroke, people must move to a cool, shaded area to rest and recover, according to the Government of Canada.

If a person is suffering from heat cramps, they must have two glasses of salty water. The government advises mixing five milliliters of salt with one liter of water — at 10 to 15 minute intervals between each glass if cramps persist.

While those who become exhausted from the heat are asked to rest in bed, if they don't recover, they must seek medical attention.

"Heat stroke is very serious. Call 911 immediately," the government advised.

As the person waits for help, it's recommended they sponge the body with cool water while letting the water evaporate to reduce body temperature.

Who is at risk during heat warnings?

People who experience the most exposure to heat, as well as youth and seniors, are the ones who are at most risk of getting a heat related illness, according to Green.

When it comes to the very young and old in particular, she explains that their "compensatory mechanisms" don’t work as well and so their body might get overwhelmed pretty easily and not be able to balance itself.

People with underlying health conditions are also more at risk such as those with breathing or heart problems and mental illness.

"The chronic condition that was correlated with death the most in the 2021 B.C. heat dome was schizophrenia," said Green.

"We don't know exactly why, but likely it's a combination of behaviors associated with the disease itself…People with schizophrenia actually had a three times mortality rate compared to the average British Columbian," she added.

During this time, western Canada "experienced temperatures up to 20°C above normal. Some provinces recorded more than 103 all-time heat records, including Canada's highest temperature ever measured in Lytton, BC (49.6°C on June 29, 2021)," the government of Canada website stated.

Other people who are at risk are those who work outdoors like construction workers, and people in the gig economy like Uber Eats.

Green added common medications like blood pressure pills and allergy medications can also affect the body's ability to regulate heat.

"It's not something that health professionals often talk about."

Anti-seizure, antidepressants and antipsychotic medications can also put people at risk. Green explained some of the medications affect cardiac output, or the person's sweat rates, and can impact fluid balance and dehydration.

"People should just be aware of that. And I'm not suggesting that anyone make any medication changes, but it just means that the person might be more vulnerable to heat-related illness and should be paying closer attention," said Green.

How to stay safe? Plan ahead

Green said it's helpful for people to develop a heat plan, especially for people who may not have air conditioning or have active cooling in their homes.

"Think ahead of time before there's an extreme heat event, what you will do in the event of extreme heat? Do you have a place where you can go that has active cooling?" she noted.

She said places like public libraries and malls have active cooling systems in place that can help protect people from the heat.

Green said people can actively cool themselves down by using wet clothes or going in the shower.

"If you have to go outside, stay in the shade and be aware, again, of the cooling centers or places that are cooled in your neighbourhood,” said Green.

During heat waves, the Government of Canada also recommends people drink fluids, especially water, and to slow down.

"Your body can’t function as well in high temperatures,” the government added.

Green said it's important that people and societies adapt to increasing temperatures that are induced by climate change and have a heat plan in place, but that shouldn't be the only focus.

"We have to tackle climate change at its roots, and that means we need to stop burning fossil fuels," she said.

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