How Cities Make Us Sick (& How to Get Better)

Is your lifestyle too clean? A researcher from the University of Colorado at Boulder and his colleagues say maybe. They’re basing the claim off the “hygiene hypothesis,” which states some microbes and infections that interact with the immune system to suppress inflammation. A lack of exposure to these microbes and infections could be hazardous to your overall health.

Inflammation is never a good thing, and an inability to suppress inflammation naturally can lead to lifelong health problems.

“Chronic inflammation can lead to all kinds of problems from irritable bowel syndrome to asthma to allergies and even depression,” Christopher Lowry, an associate professor in the CU-Boulder Department of Integrative Physiology said. “The rise of chronic inflammation and these associated disorders, especially among people living in the cities of developed countries, is troubling.”

It seems more people living in cities may be part of the problem. Lowry and his fellow researchers believe people who live in urban centers and have less access to green spaces may be more inclined to have chronic inflammation.

They hypothesize that this happens in part because people living in cities are not exposed to some infections that may help improve the immune system in the long run. These infections help prevent the immune system from triggering unnecessary inflammation like what happens during an asthma attack or allergic reaction.

The researchers aren’t condoning the abandonment of all health practices, but rather stating some exposure to certain kinds of infections will do more good than harm, while still others do more harm than good.

“The idea that we’re too clean – that gives the wrong impression,” Lowry said. “You want people to wash their hands because hygiene is important to avoid infections that are harmful.”

A key difference is the kind of infections modern city-dwellers are exposed to. Over our evolutionary history, humans were exposed to microbes and infections in three ways: from family members, from the environment, from chronic infections. These “old infections” were tolerated by the body for long periods of time – without triggering inflammation. Additionally, people picked up harmless environmental bacteria that were tolerated by the immune system.

Now, those “old infections” have been largely eliminated in developed countries, leading to more modern “crowd infections” such as measles or chicken pox that don’t lead to lower instances of inflammatory disorders.

“You don’t want the crowd infections,” Lowry said. “But you do want to find ways to increase your exposure to ‘old friends.’”

Researchers believe these “old friends,” old infections and microbes, are important to overall health. Exposure to them can help guard against inflammatory disorders. The researchers feel the best way to get exposure to the environmental microbes is to spend more time in rural environments like farms and other green spaces.


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Christine Jones
Christine J2 years ago

Makes a lot of sense to me. Many years ago in my school class of 40 kids only one kid had asthma and there were none with allergies, apart from mild hay fever. Now classes of 20 kids have several kids with serious asthma, food intolerances, severe allergies to cats and life-threatening peanut allergies. At the same time homes have smaller gardens, less pets, and are filled with anti-bacterial products. Kids are driven everywhere and don't get to splash in muddy puddles, play with neighbourhood dogs and generally be kids. Not a coincidence IMHO.

Janice Thompson
Janice Thompson3 years ago

Don't breath "City Air".

Melania Padilla
Melania P3 years ago


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ANA MARIJA R3 years ago

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Hazel G.
Hazel G3 years ago

Thanks for posting.

Rhonda B.
Rhonda B3 years ago

Thank you.

Nils Anders Lunde
PlsNoMessage se3 years ago


Marion Zerrenthin