What happens during fight and flight?

The "fight and flight" response is an evolutionary mechanism in the brain that helps humans survive. This response developed significantly during hunter-gatherer times when humans lived in more dangerous environments. It allows individuals to become significantly stronger and faster in a split second—an advantage when fighting off a wild animal or escaping danger. Stories of people demonstrating superhuman strength to save their loved ones illustrate the "fight and flight" response in action.

We speak to a leading consultant psychiatrist who explains what happens during this response.

The brain mechanism

At the core of the "fight and flight" response is the amygdala, a structure within the limbic system—the brain's most ancient and instinctive part. The amygdala governs fear responses, reacting to perceived danger before any other part of the brain can assess the threat. This quick reaction means the body prepares for action without fully evaluating whether the danger is real.

What happens in the body?

When the "fight and flight" response is triggered, several physiological changes occur:

Breathing and oxygen: The body takes in more oxygen by breathing faster and shallower, while expelling less carbon dioxide.

Heart Rate and circulation: The heart pumps blood more rapidly to deliver oxygen to the muscles, making them stronger and ready for action.

Stress hormones: Adrenaline and cortisol are released, heightening alertness and energy.

Meanwhile, non-essential bodily functions slow down. For instance, digestion halts, causing the "butterflies in the stomach" sensation. Less oxygen is directed to the brain, leading to feelings of light-headedness, dizziness, or difficulty concentrating. Although anxiety may make some people feel faint, the elevated blood pressure during the "fight and flight" response makes fainting unlikely.

Modern-day triggers

Although the "fight and flight" response is a powerful survival mechanism, it is often activated in situations where it is unhelpful. In today's world, immediate physical danger is rare, but the response still occurs in scenarios perceived as "social danger." For example, many people experience intense anxiety when public speaking, even though no physical threat exists. Research has shown that fear of public speaking is sometimes greater than the fear of death.

This reaction stems from an ancient survival instinct: if we embarrass ourselves and are rejected by others, we might risk social isolation, which historically reduced survival chances. As a result, the "fight and flight" response is often triggered by cultural fears of shame and rejection.

The response is also activated in situations involving health concerns—our own or that of loved ones—where a strong physical reaction is not particularly helpful. Unfortunately, this misplaced activation means we experience anxiety in circumstances where it would be far more beneficial if the response did not occur.