Maybe you’ve taken a deep breath before to calm yourself down—completely intuitively, without giving it much thought. But have you ever asked yourself what your body actually needs in that moment?
When we think of breathing, most of us immediately think of oxygen—the “good gas” that brings life. And CO₂? It’s often seen simply as something that needs to be expelled—a waste product.
But what if that’s not actually true? What if CO₂ isn’t just harmless, but actually crucial to your health—especially your brain?
I’ll share five surprising facts about CO₂ with you. And maybe after reading this, you’ll look at your breathing in a whole new light.
1. It’s not a lack of oxygen, but CO₂ that tells your body to breathe
Do you know that feeling of being short of breath? As if you’re not getting enough air? Most people think it’s caused by a lack of oxygen.
But that’s not true. It’s not the lack of oxygen that triggers the urge to breathe, but the rising CO₂ level in your blood. As soon as this level reaches a certain threshold, your brainstem registers: Time to breathe!
If you have a low CO₂ tolerance, you’ll feel the urge to breathe sooner—you’ll start breathing more shallowly, and often more quickly as well. This is exactly the pattern that emerges during stress or anxiety.
The good news is: You can train yourself to handle this. The more you experiment with your breathing and breathe more consciously, the more your body gets used to CO₂. And you’ll learn to stay calm, even when your CO₂ levels rise.
2. CO₂ Delivers Oxygen Where It’s Needed
You may have also heard that oxygen is important for your energy. Of course! But did you know that without CO₂, the oxygen doesn’t actually get where it needs to go?
That’s because CO₂ helps:
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keep the blood vessels open so that oxygen-rich blood can flow freely
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hemoglobin to release the oxygen again as soon as it reaches the cell (this is called the Bohr effect)
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protect the mitochondria—your cells’ powerhouses—from too much oxidative stress
Simply put: CO₂ acts like a delivery service that ensures the valuable cargo—oxygen—arrives where it’s needed. Without CO₂, oxygen gets “stuck” in the blood.
3. Too much oxygen can harm your brain
Yes, really. This finding surprised even me.
As early as 1946, Kety and Schmidt demonstrated in a study that inhaling pure oxygen reduces blood flow to the brain. Why? Because blood vessels constrict when there’s too little CO₂ present.
In contrast, breathing air with slightly more CO₂ led to significantly better blood flow. The brain’s blood vessels dilated, and more oxygen actually reached the brain.
This means: If you focus only on inhaling as much oxygen as possible without paying attention to CO₂, the exact opposite of what you want happens. Less oxygen reaches the brain, not more.
4. Doctors use hyperventilation to “shrink” the brain
It sounds almost like science fiction, but it’s reality.
During certain brain surgeries, doctors deliberately use hyperventilation—rapid, deep breathing. This causes the CO₂ level in the blood to drop sharply. As a result, the blood vessels in the brain constrict, and the brain becomes smaller and firmer. This creates more space for the surgery.
However, a 2019 study criticizes this practice. Although it’s widespread, there’s a lack of solid evidence supporting its benefits. The researchers describe it as a “double-edged sword.”
In everyday life, this means that if you frequently hyperventilate without realizing it—for example, during stressful moments—you’re literally depriving your brain of oxygen—even though you think you’re breathing “more.”
5. Conscious breathing could help your brain clean itself
While you sleep, something fascinating happens in the brain. A cleansing system—known as the glymphatic system—becomes active. It helps remove waste products like beta-amyloid, which are linked to diseases such as Alzheimer’s.
Here’s the interesting part: Studies show that CO₂ might also support this process during the day. Researchers discovered that rhythmically varying CO₂ levels stimulate the circulation of cerebrospinal fluid—similar to what happens during deep sleep.
What does this have to do with you? Practices such as slow diaphragmatic breathing, meditation, yoga, or tai chi naturally alter the CO₂ levels in your blood. This could help “cleanse” your brain while you’re awake.
Conclusion: Your breath is much more powerful than you think
From the respiratory reflex to cellular cleansing—CO₂ isn’t a waste product, but an important regulator for your body and brain.
We can stop fearing CO₂. It’s not about inhaling as much oxygen as possible. It’s about balance. And about becoming more aware of your breathing again.
Maybe today you’d like to simply observe how you breathe—without changing anything. And feel what changes within you as you do so.
Bonus Tip: Cardihaler for CO₂ Tolerance
If you’d like to dive deeper into this topic and specifically train your CO₂ tolerance, theCardihaler can help. With this portable breathing tool designed for everyday use, you can gently increase your tolerance to CO₂ and make your breathing more mindful in just a few minutes of breathing exercises.
Find out more here: Discover the Cardihaler
Give it a try! Your body will thank you for it.
