Apocalyptic images of blackened skies and landmarks shrouded in an orange haze have been beamed around the world as toxic smoke from Canadian wildfires blankets the Northeast and Upper Midwest.
Driven south by shifting winds, the smoke has travelled hundreds of miles, engulfing cities from Detroit and Chicago to Washington DC and New York and placing more than 100 million Americans under air quality alerts.
But while the eerie haze has transformed city skylines, doctors warn the greatest danger is invisible – microscopic particles in the smoke that begin infiltrating the body within minutes of being inhaled.
Officials in 19 states have urged residents to stay indoors as pollution reaches hazardous levels.
Air quality is measured using the Air Quality Index (AQI), a scale that reflects the concentration of pollutants in the air, including ozone and PM2.5 – microscopic particles around 30 times thinner than a strand of human hair that are small enough to penetrate deep into the lungs and even enter the bloodstream.
An AQI of 0 to 50 is considered ‘good,’ while anything above 300 is classed as ‘hazardous’ – meaning even healthy people are at risk of serious health effects.
But in parts of the Midwest, the scale has been blown apart. Detroit’s AQI climbed above 700, while Chicago reached almost 600 – among the worst air quality readings recorded anywhere in the world. So, just what does breathing these levels of pollution do to the human body?
Doctors speaking to the Daily Mail have broken down exactly what happens after minutes, hours, days and even years of exposure to toxic air – from the immediate effects on the eyes and lungs to the long-term damage it can inflict on the heart, brain and other organs.
Warnings are in place over toxic air as New York was among the major US cities suffering the effects of Canadian wildfire smoke
WITHIN A FEW MINUTES…
Shortly after stepping into the smoke, pollutants such as PM2.5 and ozone begin attacking the eyes, nose and throat with every breath.
Chris Turner, founder of air quality company Breathe Tech, told the Daily Mail that indoor air quality monitors detect pollution levels rising almost immediately in smoky conditions.
‘Symptom reports from users line up almost exactly with that spike,’ he said.
In the eyes, microscopic particles cling to the surface, disrupting the protective tear film that keeps them lubricated. Within minutes, they can become red, begin to sting and develop the gritty sensation many people describe as feeling like sand is trapped beneath the eyelids. Excessive watering is the eye’s attempt to flush away the irritants.
At the same time, PM2.5 particles and irritating gases scrape against the delicate lining of the nose and throat, causing a scratchy, burning sensation.
‘That’s the smoke particles and gases hitting your mucous membranes directly,’ Turner said.
But the damage does not stop there. Within minutes, the smallest particles travel deep into the lungs, where some pass into the bloodstream, triggering inflammation and oxidative stress that place strain on organs throughout the body – particularly the heart.
WITHIN AN HOUR…
Air quality monitors have deemed the air to be ‘hazardous’ in multiple US cities on as of Friday, July 17
After about an hour, those microscopic particles have accumulated deeper in the lungs, where they begin triggering more noticeable symptoms.
Dr Ahmad Abu Homoud, medical director of the Pulmonary Hypertension Center at Hackensack Meridian Jersey Shore University Medical Center, told the Daily Mail this is when people often develop a persistent cough, worsening sore throat, wheezing and shortness of breath.
‘That’s when you start hearing about chest tightness and shortness of breath rather than just irritation,’ Turner said.
For people with asthma or chronic obstructive pulmonary disease (COPD), the effects can be far more severe.
Their airways are already inflamed and hypersensitive, meaning wildfire smoke can rapidly trigger bronchospasm – a tightening of the muscles surrounding the airways – while increasing mucus production and narrowing the passages through which air flows.
‘People with asthma are hit especially hard,’ Dr Scott Braunstein, chief medical officer at Sollis Health, told the Daily Mail.
‘Wildfire smoke causes a higher level of inflammation than regular air pollution.
‘It can make inflammation harder to control with usual asthma medications such as steroids, and it can quickly cause airway spasm, increased mucus production and reduced lung function.
‘Smoke doesn’t just irritate you in the moment; it also disables your lungs’ natural defense system.’
Dr Abu Homoud added that wildfire smoke is more harmful than typical urban air pollution because it contains higher concentrations of oxidizing chemicals and inflammatory compounds, making it especially likely to worsen asthma, COPD, coughing, wheezing and chest tightness.
WITHIN HALF A DAY…
Residents are pictured out in about in Detroit, which currently has the worst air quality in the world, even with the health warnings in place
After a few hours, many people begin to notice they’re tiring more easily. Climbing stairs can leave them unusually breathless, while even light exercise may trigger chest tightness, headaches and fatigue.
That’s because the lungs have begun mounting an immune response to the pollutants, releasing inflammatory proteins called cytokines. While these proteins normally help the body fight infection, they also spread inflammation beyond the lungs and into the cardiovascular system.
‘In the circulatory system, inflammatory processes triggered early after exposure continue amplifying, leading to what’s referred to as an inflammatory cascade,’ Dr Justin Fiala, pulmonologist at the Northwestern Medicine Canning Thoracic Institute, told the Daily Mail.
At the same time, ongoing inflammation in the lungs makes it harder to absorb oxygen with every breath.
‘These changes decrease the body’s ability to deliver oxygen efficiently during physical activity while ongoing airway inflammation further limits breathing capacity,’ Dr Abu Homoud added.
‘As a result, many people experience reduced exercise tolerance, shortness of breath, chest tightness, headaches and fatigue, with individuals who have existing heart or lung disease facing the greatest risk.’
Reduced oxygen delivery to the muscles and brain can also leave people feeling lightheaded, sluggish and unable to concentrate.
WITHIN 24 HOURS…
Chicago residents are pictured wearing masks to protect against smoke from Canadian wildfires on July 16
By the end of the first day, the body’s inflammatory response is in full swing and the health effects become increasingly difficult to ignore.
‘This is typically when emergency departments start seeing the uptick – more asthma attacks, more COPD flare-ups and more people arriving with chest pain,’ said Turner.
During the 2023 Canadian wildfire smoke crisis, respiratory-related emergency department visits rose by between 17 and 30 percent during air quality alerts, according to Centers for Disease Control and Prevention data.
For people with asthma, sustained exposure can sharply reduce lung function, leading to persistent coughing, wheezing and chest tightness.
In those with COPD, smoke can paralyze the tiny hair-like structures known as cilia that normally sweep mucus and contaminants from the airways, increasing the risk of chest infections.
But the danger extends beyond the lungs. By this stage, prolonged inflammation and damage to blood vessels have also begun raising the risk of cardiovascular emergencies.
‘Cardiovascular risks, including heart attack, stroke, arrhythmias, heart failure, cardiac arrest and cardiovascular death, all rise – particularly in older adults and people with pre-existing heart or lung disease,’ said Dr Abu Homoud.
‘The risk increases as wildfire smoke PM2.5 concentrations rise.’
Dr Fiala notes that even ‘for people without underlying lung disease, breathing may become more labored after a day of PM2.5 exposure, as inflammation in the airways makes it harder to take full breaths.’
AFTER A FEW DAYS…
After several days of breathing polluted air, the lungs’ natural defense system begins to break down.
Dr Abu Homoud said that prolonged exposure damages mucociliary clearance – the process by which mucus traps inhaled particles and tiny hair-like structures called cilia sweep them back out of the airways.
As that first line of defense weakens, the lungs become increasingly vulnerable to infection.
‘The damaged respiratory lining becomes more susceptible to infections such as influenza, pneumonia, bronchitis and COVID-19, especially in children,’ he said.
Children are particularly vulnerable because their immune systems and lungs are still developing, while older adults and people with underlying heart or lung disease also face a greater risk of serious illness.
Meanwhile, inflammation continues to build throughout the cardiovascular system, placing increasing strain on the heart and raising the risk of heart disease and dangerous heart rhythm disorders known as arrhythmias.
Left untreated, severe arrhythmias can reduce the heart’s ability to pump blood effectively, increasing the risk of heart failure, cardiac arrest and sudden death.
AFTER MONTHS OR YEARS…
A Chicago resident bikes along Lake Michigan on July 16 during wildfire smoke warnings
Even after the skies clear, the effects of repeated or prolonged exposure can continue to unfold.
‘Repeated or long-term wildfire smoke exposure contributes to the development of chronic diseases,’ said Dr Abu Homoud.
Persistent inflammation gradually damages the lungs, scarring the delicate air sacs and airways and permanently reducing lung capacity.
In diseases such as emphysema, the smoke destroys the elastic fibers that keep the airways open, trapping stale air inside the lungs and making every breath less efficient.
But the damage is not confined to the respiratory system.
Years of exposure have also been linked to heart disease, stroke and cognitive decline as microscopic particles continue to trigger inflammation throughout the body.
Some of the smallest particles can even travel from the lungs into the bloodstream and, in some cases, reach the brain via the olfactory nerve.
Researchers believe this chronic inflammation may accelerate the build-up of amyloid plaques associated with Alzheimer’s disease, helping explain why long-term exposure has been linked to a higher risk of dementia.
Air pollution is also a recognized cause of lung cancer.
According to the Union for International Cancer Control, long-term exposure increases the risk by up to 25 percent, making polluted air one of the leading risk factors for lung cancer among people who have never smoked.
The consequences may not be purely physical. Dr Scott Braunstein said prolonged wildfire smoke exposure has also been linked to higher rates of anxiety, depression and post-traumatic stress disorder, particularly in communities repeatedly affected by major wildfire events.
‘Additionally, pregnancy, which relies on healthy vessels to deliver nutrients to the developing fetus, may also be riskier with high cumulative wildfire PM2.5 exposure,’ Dr Fiala said.
But much of the picture is still unknown. ‘More research is needed to better understand the long-term health effects of wildfire smoke,’ Dr Jacob Fox, pulmonologist at the University of Colorado School of Medicine, told the Daily Mail
… AND HOW TO PROTECT YOURSELF
‘Wildfire smoke may be most dangerous to children, older adults, pregnant women, and outdoor workers exposed to large amounts of smoke, as well as individuals with underlying chronic lung and heart diseases like asthma and coronary artery disease, respectively,’ Dr Fox said.
The most effective way to reduce your risk is to limit your exposure to polluted air, experts say.
Stay indoors whenever possible, and keep windows and doors closed when AQI readings are in the ‘Unhealthy’ or ‘Hazardous’ range.
If you have air conditioning, set it to recirculate indoor air rather than drawing air in from outside.
A portable air purifier fitted with a HEPA filter can remove most fine particulate matter (PM2.5) from indoor air. If you do not have one, spending time in public buildings with filtered air, such as libraries or shopping malls, can reduce exposure.
If you have to go outdoors, wear a well-fitting N95, KN95 or KF94 mask. Cloth masks and surgical masks offer little protection against the tiny PM2.5 particles found in wildfire smoke.
Avoid strenuous exercise outdoors. Running, cycling or heavy manual work causes you to breathe faster and more deeply, allowing more pollution to reach the lungs.
Keep an eye on the AQI. Check local air quality before heading outside. Once AQI rises above 100, sensitive groups such as children, pregnant women, older adults and people with asthma or heart disease should reduce outdoor activity.
Above 150, everyone should limit prolonged exposure, and above 300, officials recommend avoiding outdoor activity altogether.
‘Because of these risks, symptoms like difficulty breathing, chest pain, inability to move a part of the body, or slurring of words should be taken very seriously and should be evaluated by a medical professional,’ Dr Fiala told the Daily Mail.
