Biology of Anxiety

Updated: Jul 3, 2019

Anxiety developed for a good evolutionary reason, if we go into an unfamiliar situation, or one that might be dangerous, it’s wise to be extremely careful and ready to deal with whatever might happen.

Our unconscious mind has two roles:

1. To keep us alive

2. To reduce our anxiety

However they are in this order and therefore if our unconscious mind has a belief that the anxiety will keep us safe, then it will create anxiety.

Anxiety makes us ‘hyper-vigilant’, in other words we are super-sensitive to changes around us, especially noises and movement, this means we are more likely to detect a threat or predator if there is one around and we can bring about a ‘stress response’ quickly to help us avoid it or protect ourselves.

In short bursts and appropriate circumstances, anxiety is a survival strategy. However, in inappropriate circumstances or experienced consistently over long periods of time, it ceases to be a beneficial process and begins to erode our physical and emotional health and well-being.

Most of the stresses faced by our primitive ancestors were short, sharp shocks: the sort of danger that occurs if a predator attacks or a rock fall happens. To survive, they either had to be able to escape as quickly as possible or to fight off the threat.

Over time they evolved what we now refer to as ‘the stress response’ or otherwise known as ‘fight or flight’, to help them to do this.

This reaction is still a part of us; in times of stress, our bodies release stress hormones which make physical changes in the way our bodies operate. The stress response triggers the release of chemicals called catecholamines; these include hormones like adrenaline and cortisol which affect many different systems within the body:

The Short-term Effects of Stress:


  • Digestion of sugars – To get as much sugar into the blood as possible to give a surge of energy

  • Heart rate and blood pressure – To get as much blood pumping around the body as quickly as possible

  • Breathing rate – To get as much oxygen around the body as quickly as possible

  • Blood supply to muscles, especially in the arms & legs -the muscles required to either fight or flight

  • Blood clotting ability - To reduce lethal bleeding


  • Sensitivity to pain

  • Digestion (except sugars)

  • Blood supply to the skin

  • Blood supply to the ‘modern’ parts of the brain (language/logic/planning)