Climate

How to watch for the hidden symptoms of extreme heat

Climate change is making summers in Canada hotter, with more days of extreme heat and fewer nights that let our bodies cool down. That can have serious health consequences, and doctors say people aren't fully aware what to watch for.

Heat stroke is rare, but there are other symptoms doctors say people often aren't aware of

Forehead with sun superimposed on top of it.
Heat-related illness can have a number of symptoms doctors say people may not recognize, from rash and swollen feet to confusion and loss of consciousness. (CBC Graphics Illustration, Shutterstock)

Climate change is making summers in Canada hotter, with more days of extreme heat and fewer nights that let our bodies cool down. 

The consequences of extreme heat can be severe: last year, more than 600 people died during the heat dome in British Columbia and, in 2018, up to 70 deaths in Quebec were linked to a heat wave there. 

Research suggests Southwestern Ontario experienced a 22 per cent increase in emergency department visits during periods of extreme heat, according to data analyzed from 2002 to 2019.

What temperature threshold triggers a heat warning varies depending on your location, but the symptoms of heat-related illnesses remain the same — and doctors say people aren't fully aware what to watch for.

"Heat-related illnesses arise when an individual is exposed to environmental heat and their own body is not able to accommodate or acclimatize quickly," said Dr. Justin Yan, an emergency physician in London, Ont.

Yan has treated several patients experiencing heat-related illnesses in the emergency room. He says these symptoms are potentially life-threatening and should be taken seriously when they happen. But he cautioned that it's not just about heat stroke.

"There's a spectrum of heat-related illness symptoms." 

Some cities open emergency cooling centres during heat waves, like this one in Toronto in May 2020, recognizing the impact of extreme heat on human health. (Michael Wilson/CBC)

A spectrum of symptoms

Heat-related illnesses can range from mild, requiring cooling and rehydration, to severe — requiring emergency medical treatment. 

Yellow zone: Mild heat-related illness

  • Heat edema occurs when blood vessels dilate and blood accumulates in the hands and feet due to gravity, says the U.S. Centers for Disease Control and Prevention (CDC). People with diabetes, cirrhosis, and heart conditions are at a higher risk. The treatment is to elevate the swollen area to drain it.
  • Heat rashes occur when sweat glands get blocked or inflamed, so the CDC recommends keeping the rash area dry and applying powder to increase comfort.  Yan says he's seen babies in the ER with heat rashes because they are bundled up a bit too much. "Not just babies, but adults as well can get rashes more commonly in sweaty areas like your groin, your neck, or your armpits." 
  • Heat cramps happen when the body loses salt and water, and is treated by replenishing carbohydrates and electrolytes with a snack, water or sports drink.
Swollen ankle, rashes on arm, women holding stomach

Orange zone: Moderate to severe heat-related illness

  • Heat syncope, when someone feels light-headed after standing up, is treated with rest and relief from heat, sitting or laying down in a cool place, and slowly drinking water, clear juice or a sports drink. 
  • Heat exhaustion happens when you experience an excessive loss of water and salt, usually through sweating. It is treated by cooling down with cold packs, washing the head, face, and neck with cold water, and frequently sipping cool water. 

Yan says the most common symptom he sees is heat exhaustion. 

"People will feel lightheaded, they might have a bit of a headache, feel tired and weak, they may feel nauseated. They could pass out," he described. 

"What is actually happening is the body is sending a message to drink some water and get to a cool environment."

Man holding forehead and woman sitting at bench looking tired

Red zone: Severe heat-related illness 

  • Heat stroke happens when the body's cooling mechanism fails so you stop sweating, and internal temperature heats up. Emergency medical care is required at this point. It helps to cool down with cold water, an ice bath, and soaking clothes with cool water. 
woman passed out with person holding her head and hand.

Outdoor exertion in the heat is risky

We may be tempted — or required — to be outside during hot, sunny days, but too much exertion can be dangerous, doctors say.

"I've had a patient work a very physical job in the heat and describe feeling just terrible, almost passing out. They may have actually experienced a heat-related illness by definition but were not aware of it," said Dr. Kristin Clemens, an endocrinologist and clinician-researcher at Western University in London, Ont.

Someone working outside during periods of high heat may not be able to respond to their body's desire to seek a cooler environment. 

"Construction workers, people who are working outside, roofers, people who don't have the ability to say, 'I need to cool off, or get some water, or get to a colder environment.'"

Yan says the most severe cases he's seen are "people who are fainting while on the job during construction."

A construction worker uses a misting fan to cool down at a work site in Vancouver during B.C.'s deadly heat dome on June 28, 2021. (Ben Nelms/CBC)

Diabetes is impacted by high heat

Patients with endocrine disease, including diabetes, are at higher risk of heat-related illness, says Clemens.

She previously published research on seeing more cases of low blood sugar during hot months. Though the reason is scientifically complex, she says "we know that insulin absorption, metabolism, and diabetes supplies are impacted by heat."

Dehydration and kidney injury due to high heat exposure can lead to a change in medication metabolism, which then leads to low blood sugar levels, she said.

Some patients also struggle to properly store their medication.

"Sometimes I've prescribed particularly effective medications to patients, but they have had difficulty finding a place to store it safely from heat exposure, particularly where their housing conditions are poor." 

WATCH | Your neighbourhood can determine how hot your home is:

Why your neighbourhood may determine how hot your home is

2 months ago
Duration 5:28
Extreme heat exacerbated by climate change is killing Canadians in their homes. But how well equipped you are to combat rising temperatures has a lot to do with your income level — and that of your neighbourhood.

Feeling bad? It could be the heat

Clemens suspects people may not understand their symptoms are due to the heat because they may not know what a heat-related illness is. 

Mild heat-related illness has a simple solution: a cool environment. If people aren't acknowledging their symptoms due to work expectations, because they don't realize their symptoms are due to the heat, or because they simply don't have access to a cooler area, they may not seek this easy fix. 

"There are some vulnerable and marginalized populations that are coming in more often. The elderly and some of our large homeless population," said Yan.

Some of these patients find relief in the waiting room of the hospital without a need for treatment from a physician.

"There are some people who do feel dizziness or cramps and after waiting in our emergency departments for a couple of hours they feel perfectly fine," said Yan.

Rather than going to the ER, recognizing these symptoms are due to heat means seeking a cooling station instead, provided they're accessible. According to Yan, this also means less panic over mild heat-related symptoms.

Dr. Justin Yan sitting at his work desk in London, Ontario, with a stethoscope around his neck. He is writing clinic notes. and smiling into the camera.
Dr. Justin Yan, an emergency physician in London, Ont., regularly treats patients with heat-related illness. (Submitted by Justin Yan)

Heat stroke is rare and deadly

Yan says there is a misunderstanding about heat strokes and that the term is often misused by the public. They're rare, very serious — and require emergency medical care.

"People with heat stroke come in with such a degree of heat-related illness that their bodies are no longer able to do anything to cool themselves off."

"It takes quite a bit to cool someone down if they have a true heat stroke."

It is a life-threatening emergency, with symptoms of confusion, loss of consciousness, and very high body temperature with skin that's either dry or sweating profusely.

"If they come into the emergency department with organ dysfunction, that's not reversible. People certainly can die from that."

The CDC advises that if you suspect someone has heat stroke, you should call 911 and take immediate steps to cool them down.

 

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