Strictly speaking, stress doesn’t cause ulcers. A bacterium does. Robert Sapolsky, author of the highly influential book Why Zebras Don’t Get Ulcers, has been clear about that. But his famous phrase was never really about ulcers. It was about something more fundamental: why the human stress response is so easily, and so chronically, activated—long after any real danger has passed, and even in the absence of any danger at all. Unlike zebras, we humans get stressed by the mere thought of future threats—events that haven’t occurred and may never occur. And while the zebra stress response is primarily triggered by real and immediate threats to their physical survival (e.g., a lion or other predator), we humans also get stressed by threats to our psychological well-being—a verbal slight, a conflict with our partner, being ghosted on a dating app, or a humiliation at work. We even get stressed by situations that are simply inconvenient but not actually threatening, like sitting in traffic, waiting in line to get a new driver’s license, or missing a bus.

We have become masters at becoming stressed and remaining stressed for long periods of time. That may sound harmless or merely annoying, but it’s far more serious than that: Chronic stress weakens the immune system, leaving us vulnerable to illness and premature death. It increases the risk of substance abuse and chronic insomnia, impairing everyday functioning. Neurologically, chronic stress is related to the death of neurons in the hippocampus, a brain structure critical to healthy memory. And it has been linked to shortened telomeres, the caps on our chromosomes that protect our DNA. Telomere erosion leaves us vulnerable to a host of age-related diseases. And finally, stress harms........

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