In July of 1995, something unprecedented went down in Chicago- a heat wave that ground the entire city to a halt. The heat index, which measures how the temperature feels to us, jumped to a record-setting 126 degrees Fahrenheit.

Chicago was unprepared.  As residents cranked up their air conditioning the spike in electrical use led to power outages across the city.  Cars broke down and the city's emergency response units were overwhelmed.  Ambulance services sometimes took two hours to arrive on the scene, and then had trouble finding somewhere to take people because hospitals were full and closing their doors to new patients. The oppressive heat lasted about week and it's estimated that up to 739 Chicago residents lost their lives from heat-related complications. 

But follow-up reporting revealed that the impact wasn't random.  A map of deaths showed that the communities most affected were those that suffered from a lack of infrastructure and community resources mostly in the south and west of the city. 

Twenty-five years later, Chicago found itself staring down a different headline-grabbing crisis: the COVID-19 pandemic. Eartly in the pandemic, a local news station in Chicago analyzed the number of COVID deaths in different neighborhoods across the city.  And an interesting trend appeared. That map that emerged showed showed similarities to the map of Chicago's death toll from the 1995 heat wave. These maps describe two distinct health outcomes at two different moments 25 years apart. Yet the story they tell is the same: people who live in certain neighborhoods have faced measurably worse heath outcomes than those in other neighborhoods. To help understand why, we need to look at the role that our environment plays in determining our health.

Hi, I'm Vanessa Hill and this is Crash Course Public Health! [INTRO MUSIC]

We often think about environment as the world outside our bodies. Like, we think of ourselves as being in an environment: where our skin stops, our environment begins. But we don't always consider the ways that our environment is sort of... part of our bodies.

Sure, my body is mainly made up of... me. But all that oxygen and water that my body depends on comes from somewhere. Out bodies are biological machines, built to turn our environments into stuff we need to survive. It's what bodies do!

But when that environment becomes contaminated or conditions become too extreme, our health may be put in jeopardy. The environmental factors that affect our health outcomes are what we are calling the environmental determinants of health.

We can divide these determinants into two major categories: the ones related to our natural environment, and the ones related to our built environment.  Our natural environment is all that non-human-made stuff around us, like forests and mountains.  On the other hand, our built environment is is the environment we tend to think of as "human-made," like our homes, streets, or even miniature golf courses! When thinking about our environment, public health experts generally consider how our built and natural environments come together to influence a population's overall health.

For example, while we know that the air we breathe and the water we drink aren't human-made, we can recognize that they are human-influenced!  Like if we take in a deep breath of air, we're mostly breathing in nitrogen and oxygen, but not only those things. A closer look reveals there's a whole bunch of other stuff in that breath too. 

Air pollution is the stuff in the air that is harmful to the health of both humans and the planet. One major airborne pollutant on our public health radar is particulate matter, or PM. These are particles like dust or smoke that are too small to be seen with the naked eye, and come from things like car exhausts and construction sites.

This is small enough to work its way into our lungs or even infiltrate our bloodstream. The smallest of these particles can be 30 times thinner than a strand of human hair. And it turns out when you're that small and light, you can hang around in the air for weeks at a time, sometimes traveling hundreds of mile. Which is how smoke from a wildfire in Callifornia can travel over 2,000 miles to New York City, affecting the air quality across the U.S.

Now, when we picture air pollution, we tend to imagine cities full of gas-guzzling cars and smoke-spewing factories.  But air pollution can come from other, less expected sources that aren't right outside our front door. 

One review found that, because of traffic-related pollution like car emissions, children living as far as 500 meters, or about a third of a mile, of a busy road can experience negative health outcomes, like exacerbated asthma. The same report estimated that as much as 45% of people in large cities in North America live within that distance from a busy road. And the World Health Organization reports that 99% of the global population breathes air that exceeds their guideline limits for outdoor air pollution, which contributes to as many as 4.2 million deaths per year.

And air pollution isn't just outdoors.  It's in our homes too! Some of that can come from outside elements coming in, but some of it is introduced by the activities done inside our homes. As we cook and clean, we're actually introducing potentially harmful particles and chemical compounds into the air, which can hang around long enough to eventually work their ways into our bodies.

Gas-based cooking is one of the biggest culprits, because it releases things like smoke particles and carbon dioxide that cna stick around our homes. Even baking a cake in a gas oven can emit up to double the levels of the potentially dangerous gas nitrogen dioxide (NO₂) that US regulators like the EPA consider safe for our lungs.

Then there's the problem of water. You might have heard of it.  It's, you know, most of what you are. Like air, water is part of our natural environment. But the systems we've developed to deliver water to our homes, like plumbing, come with their own set of risks.

Water pollution happens when our water supply becomes contaminated with harmful substances. Some forms of water pollution feel pretty obvious, like Coca-Cola can bobbing down a river or the oil spill in the Gulf of Mexico back in 2010. But others aren't so obvious, iek when lead leaches out from our pipes and into our drinking water, or when fertilizer runs off into a river.

When it comes to our water supply, one of the major pollutants that have public health experts on high alert are per- and polyfluoroalkyl substances, or PFAS. Sometimes called "forever chemicals," these man-made pollutants have a super strong chemical make-up that prevents them from breaking down naturally in the environment. Over time, these chemicals can seep into groundwater, eventually working their way into our drinking water. And because they're tough to break down, many household water filters struggle to totally eliminate these chemicals from our water supply.

There's a lot we still need to learn about the long-term effects of PFAS on the human body. But early findings suggest that PFAS could trigger negative health outcomes ranging from altered brain development to cancer. More than 4,500 of these chemicals are currently used around the world, in everything from non-stick pans to firefighting foam. 

Now, wen it comes to predicting and improving the health of a population, one of the biggest factors to consider is the environment in which our homes exist: our neighborhoods. For instance, we know that some people living in the West End of Chicago had it worse than others during the 1995 heat wave, but it wasn't the same in every neighborhood in that area.

Let's go to the Thought Bubble to see why. In 2002, American sociologist and urban studies expert Eric Klinenberg published a book comparing two neighborhoods impacted by the heat wave: North Lawndale and South Lawndale. Both neighborhoods had similar populations of elderly people as well as similar levels of people living in poverty- which are factors associated with higher heat-related deaths.

But when Klinenberg looked at the heat-related deaths in the two neighborhoods, he found North Lawndale experienced heat-related deaths at a rate 10 times higher than South Lawndale. Compared to South Lawndale, North Lawndale had significantly more abandoned buildings, empty lots, and shuttered storefronts.  Fewer community buildings like banks and grocery stores meant that residents without air conditioners in their homes likely had difficulty locating air conditioning in public places to find relief from the heat. 

In addition, North Lawndale had sidewalks that were in far worse condition than South Lawndale, which suggested that older residents who don't drive might have been reluctant to leave their homes for fear of falling while walking, or unable to leave their homes because damaged sidewalks can be impossible to navigate with a wheelchair.

North Lawndale also had higher rates of violent crime, which may have meant that residents were less likely to leave their homes for  fear of robbery while they were away.  They were also less likely to crack open the windows or sleep outside- strategies that might have helped them cope with the heat wave.

These infrastructure challenges and high rates of violent crime also had social implications that came into play during the heat wave. The absence of a connected community meant that residents had fewer opportunities to build connections with their neighbors. This lack of social cohesion put the residents at risk of severe social isolation, and made them less likely to have a social network that they could lean on during the heat wave. 

Faced with a lack of suitable options, residents remained in the sweltering heat of their homes. And for many, this proved deadly.  Thanks Thought Bubble.

So there's no escaping the influence our environment has on our health. But we do have some say in how we manage and build our environments- and in who those environments protect. Decades of studies have found that marginalized and low-income populations are disproportionately exposed to environmental pollutants, often because they don't have the support from their government or communities to escape or improve their environments, and because their communities are often targets for things like hazardous waste sites. Enter: environmental justice!

American environmental justice activist Dr. Robert Bullard defines environmental justice as the principle that "all people and communities are entitled to equal protection of environmental and public health laws and regulations." In short, the environmental justice movement calls for us to address our shared history of racism, exploitation, and segregation to create an environment that's healthy for everyone. And just ot be clear, this means improving environments everywhere.
Environmental justice also demands that we find solutions for these unfair and preventable differences in health outcomes. Not tomorrow. Not eventually. Right now.

What makes the environmental justice movement one of the biggest challenges facing our planet. Climate change is the change in average weather patterns in a region over a long period of time. In the last two centuries alone, human activity and growth has caused our climate to change at a faster pace than it has even in the last 65 million years. In fact, the Union of Concerned Scientists estimates that if humans continue to alter the climate at the rate we are now, we could see events like that Chicago heat wave as often as three times per year by the end of the century.

Now, climate change is a global problem, and it affects all of us. But its effects will always weigh most heavily on communities not equipped with the same tools and support as others. These are often groups that have ancestral ties to a particular location, who can't afford to relocate, or who face other health challenges on top of the ones presented by their environment.

The good news here is that today, public health researchers are working to make the environment work for our health- not against it. Policymakers can work with scientists to create regulations around what we put into our water and air. Communities can invest in cooling stations and community centers where people can cool off on a hot summer day.

But maybe most importantly, we can continue to better understand and address the parts of our society that make the environmental determinants of health affect us unequally in the first place- namely the social determinants of health.  More on that in the next episode.

Thanks for watching this episode of Crash Course Public Health, which was produced by Complexly in partnership with the American Public Health Association. If you want to learn even more about Public Health, head over to APHA's YouTube channel (youtube.com/APHAorg) to watch "That's Public Health" a series created by APHA and Complexly.

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