To understand the impact of self-compassion on our bodies, we need to know the neurological basis of our emotion regulation. Research distinguishes between three emotion regulation systems: the threat/defence system, the resource-seeking, drive-excitement system, and the soothing, contentment, safeness and connection system. For simplicity, in the jargon of compassion-focused therapy, the defence system is called red, the resource-seeking system blue, and the soothing system green.
The role of the 'red system' is to quickly detect and respond to threats. This is our default system, genetically programmed and evolutionarily advantageous. When our ancestors were faced with an imminent threat to life, this system was responsible for the fight or flight or freeze response when activated, and for the freeze response when deactivated. In the event of an imminent threat to life, a rapid response and immediate mobilisation of all the body's energy is required. 

To do this, attention and thinking are narrowed down to the only possible response, and physiological processes that are not necessary for escape are slowed down or stopped. The amygdala and the hypothalamo-pituitary-adrenal axis (HPA) are responsible for the red system and are linked to the functioning of the reptilian brain, which is already present in reptiles. Adrenaline plays an important role in this process. The main emotions triggered by the red system are anger, anxiety, fear, shame and disgust.
The 'blue system' is responsible for evoking pleasant emotions, with the aim of motivating and encouraging us to acquire the resources we need to survive and thrive. It involves the brain's dopaminergic system. The emotions it evokes are excitement and exhilaration. It is responsible for self-worth.
The functioning of the blue and red systems are closely linked.
When we strive to achieve our goals, the blue system determines our emotions. It gives us excitement in the struggle and when we succeed, it plays a role in the pleasant emotions associated with positive self-esteem. However, when we encounter obstacles that prevent us from achieving our goals, we perceive this as a threat and the red system is activated.

Another example of how the two systems are closely interconnected occurs when we experience unpleasant emotions regulated by the red system: we feel sad, anxious, dissatisfied with ourselves. We often try to overcome these unpleasant emotions by engaging in some kind of activity. We set out to achieve a goal, and this activates the blue system and reduces the unpleasant emotions generated by the red system. The blue system plays an important role in emotion regulation and therefore psychological well-being, but in the long term it can have harmful consequences if it is the only system we rely on to reduce our unpleasant emotions. The blue system has a danger: if used as the sole regulator of unpleasant emotions, it can lead to the development of substitute actions and addictions.
The functioning of the "green system" is linked to oxytocin. The contentment it induces is a form of happiness, which occurs when we feel safe and have nothing to fight for. It is different from a state of low threat, which is experienced as boredom or a kind of emptiness. The latter system plays an important role in compassion, as it is related to kindness, love and social relationships. The emotions aroused by the green system are: contentment, peace, tenderness, warmth of heart, a sense of freedom.

To experience how these three systems work, it can help to imagine three different situations in succession: a conflict with someone, an experience of success, and being at home in a safe place with loved ones, with nothing to achieve but to relax in their presence. We can pay attention to the emotions we feel, what we feel in our body, whether our heart rate changes, our breathing, our muscle tone.