Why Do We Gasp When We're Surprised or Alarmed?

If you get caught off-guard by a sudden bang, or an unexpected tap on the shoulder, or the sight of a spider high-tailing it across the floor of your shower, there’s a good chance that you’ll let out an audible gasp. That sharp intake of breath is often an involuntary reaction to surprise and alarm. But why do we do it?

Gasping is tied to an innate survival mechanism, hardwired into humans through evolution: the fight-or-flight response. When faced with a potential threat, our bodies start preparing to react, either by engaging with the danger or getting away as quickly as possible. Within an instant, a complex chain of biological events takes place—and a small, almond-shaped region of the brain called the amygdala is responsible for ringing the first alarm bell. 

When we hear or see something threatening, the amygdala sends distress signals to the hypothalamus, known as the brain’s “command center” because it helps regulate important bodily functions. The hypothalamus triggers the sympathetic nervous system, which is the driving force in our reaction to danger or stress. 

Once the sympathetic nervous system is activated, the adrenal glands start pumping hormones, including adrenaline, into the bloodstream. Driven by this surge in adrenaline, the body undergoes numerous changes designed to help us think or act quickly. Our pupils dilate to let in more light and allow us to see better. We breathe more quickly so we can take in as much oxygen as possible. Our hearts start racing, pushing oxygen to major muscle groups and other organs that might need to kick into high gear to deal with a possible threat. 

Gasping in shock—an emotion that is closely linked to fear—may similarly prepare us for go time. The physiologic changes that are triggered by the fight-or-flight response cause the body to use oxygen more quickly, according to BBC Science Focus Magazine; a deep inhale may provide an extra jolt of oxygen in these moments of heightened stress.

Since the days of our ancient ancestors, humans’ fight-or-flight response has helped us survive dangerous situations. But it can get triggered by things that don’t pose any real threat. So after that initial gasp of surprise, take a deep breath and try to make peace with the creepy crawly invading your space—it’s probably pretty keen to get away from you, too.

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