You are probably aware of the concept of second-hand smoke, which increases the risk of disease and death. You should probably be aware of another deadly scourge: second-hand stress.

Natural selection has wired us to sense the stress of others and make it our own. If you are a gazelle and you don’t freak out when others around you do, then you might be the one about to be consumed by a predator you haven’t seen yet. Animals detect the stress of others through various sensory signals such as alarm calls, olfactory cues, or visual behaviors. Plants detect distress signals of others in the form of ethylene gas that activates their own stress response (fittingly, second-hand smoke contains ethylene). The ability to detect second-hand stress is a survival instinct that can promote evolutionary fitness.

Since our culture is evolving faster than our ability to biologically evolve, our tendency to absorb surrounding acute stress cues to activate our own stress response can produce maladaptive responses. We rarely face actual threats to our survival anymore, but illegitimate cues of stress abound around us, triggering our inherited factory settings. For example, we helplessly rubberneck trainwreck events—often contrived by media for attracting attention and profit—despite their remote connection to our personal survival.

Chronic stress is already known to contribute to disease and death. Second-hand stress can render such disease contagious. That means that the second-hand stress you get from a chronically stressed-out co-worker can adversely affect your health, not unlike that from a nearby smoker. Similarly, bringing distress home can activate stress response—and potentially, disease—in loved ones through second-hand stress.

You’ve probably been asked by your doctor at annual checkups about any family history of chronic diseases such as heart disease, hypertension, and diabetes. The common assumption is that these diseases get transmitted through our genes. No doubt, genes play a role in these diseases, but be aware that second-hand stress may be an additional way that such stress-mediated diseases follow familial lines.

On the flip side, certain social behaviors such as humor and altruism can spread stress reduction among others in the group. In a way, these behaviors represent contagious therapies that can spread improvements of chronic, stress-mediated diseases. The contagious nature of this kind of socially-spread clinical benefit contrasts with the mainstream model of treating chronic diseases with drugs, a benefit that is not contagious.

Bottom line, be mindful of second-hand stress. If you can, try to reduce exposure to chronically stressed out people to protect yourself. And protect others by not emitting your stress to them.

Originally published in This View of Life.