When most people think about carbon dioxide, they associate it with pollution, breathlessness, or the waste product we exhale. But there's much more to CO₂ than meets the eye. In fact, this often misunderstood gas plays a subtle but powerful role in how our nervous system regulates stress, calmness, and emotional well-being.

At the center of this connection lies the autonomic nervous system, which is divided into two main branches: the sympathetic and the parasympathetic. The sympathetic system gears us up for action, referred to as the fight-or-flight response. The parasympathetic system helps the body relax, recover, and return to balance. It's the calm side of the nervous system, responsible for digestion, rest, and repair. The sympathetic system is stepping on the gas pedal whereas the parasympathetic system is like hitting the brakes.

Now here's where CO₂ comes in. Carbon dioxide isn't just a waste product. Our bodies actually rely on a certain level of it to function properly. In particular, mild increases in carbon dioxide can trigger the parasympathetic system. This happens because CO₂ has a direct influence on the respiratory control centers in the brainstem. These centers are constantly monitoring CO₂ levels in the blood, adjusting our breathing rate accordingly. In fact, the need to breathe is not from a lack of oxygen because we don’t have oxygen sensors. We have CO₂ sensors, so as CO₂ rises, that is what stimulates us to breathe.

When we breathe slowly and gently through the nose or practice controlled breath-holding, CO₂ levels rise slightly. This modest rise doesn't create stress but instead reduces the drive to over-breathe. As the body senses that it's safe to slow down, parasympathetic activity increases. Heart rate lowers, muscles relax, and the mind becomes more centered. This is one reason breathwork techniques are so effective at calming anxiety and reducing stress-related symptoms.

Physiologically, when CO₂ rises we become slightly more acidic and the CO₂ sensors tell the vasculature to dilate so as to get rid of too much CO₂. So if you’ve ever been dizzy from breathwork, it’s because blood is draining from your head. Conversely, if you don’t have enough CO₂, the vasculature constricts as an attempt to hang on to more CO₂. So blood pressure rises, and this can also cause dizziness.

However, the relationship between CO₂ and the nervous system isn't entirely one-sided. If CO₂ levels rise too much or too quickly, the effect is very different. Instead of promoting calm, it triggers a sympathetic response. This happens because a sharp rise in CO₂ causes air hunger and a sense of suffocation, which naturally activates a fight-or-flight reaction. On the flip side, if CO₂ levels fall too low, such as during hyperventilation, the body may also become anxious and restless, again stimulating the sympathetic nervous system. This shows us that balance is key. A slight increase in carbon dioxide can help settle the nervous system, but extremes in either direction lead to instability.

The takeaway here is that carbon dioxide plays a regulatory role in our nervous system that goes far beyond its role in respiration. When managed gently through breath awareness or guided breathwork, CO₂ becomes a tool for encouraging parasympathetic dominance. This can result in a calmer mind, a more stable mood, and even improved physical health.

The majority of people in western society live in a chronic sympathetic state. Getting more parasympathetic activity is likely a good idea if this is you. In fact, the rise in autoimmunity we are seeing is a result of the dysregulation of the nervous system. For some, breathwork may be a beneficial adjunct in helping to regulate the nervous system.

There are several ways to do this. We like to do box breathing. This is how to do it:

You can do this while laying down, or to add a bit of challenge, you can do it while walking like I did in the video.

Improve Vagal Tone with Breath Holds