Physiological Sigh

What Is the Physiological Sigh?

The physiological sigh is a natural, powerful breathing reflex: a double inhale followed by a slow, full exhale through the mouth. It happens spontaneously every few minutes and helps reopen tiny lung air sacs (alveoli), improving oxygen exchange and clearing carbon dioxide.

Performing this sigh on purpose was popularized by Dr. Andrew Huberman, a Stanford neuroscientist known for translating brain science into practical tools, and Dr. David Spiegel, Stanford’s Associate Chair of Psychiatry and expert in mind-body medicine.

How It Helps Manage Stress

When done intentionally, it creates a powerful calming effect by:

• Reinflating collapsed alveoli: The first deep inhale expands most of the lungs. The second, shorter inhale helps open the remaining air sacs that didn’t fully inflate. This “last sip” of air boosts oxygen exchange and helps clear carbon dioxide more effectively.
  

• Lowering carbon dioxide (CO₂) levels: High CO₂ in the blood is associated with feelings of stress and anxiety. The extended exhale that follows a physiological sigh helps expel excess CO₂, leading to an immediate sense of relief.
  

• Activating the parasympathetic nervous system: The long, slow exhale stimulates the vagus nerve, which helps shift the body out of “fight or flight” and into a more relaxed “rest and digest” state.

Together, these changes help regulate your internal stress response within seconds.

This simple technique has been shown in clinical studies to lower stress, improve mood, and even enhance heart rate variability with just a few minutes of daily use.

How to Perform It

1. Breathe deeply in through your nose.

2. Immediately take a second, smaller sip of air through the nose to fully inflate your lungs.

3. Exhale slowly and completely through your mouth.

4. Repeat this cycle as needed until you feel grounded.

   
   

Watch health coach Robert demonstrate it below:

Huberman, A., Spiegel, D., Kwon, D., & Mishra, J. (2023). Brief structured respiration practices enhance mood and reduce physiological arousal. Cell Reports Medicine, 4(2), 100895. https://doi.org/10.1016/j.xcrm.2023.100895

Huberman Lab. (2022, December 19). Breathwork protocols for health, focus, and stress relief [Podcast episode]. Huberman Lab. https://www.hubermanlab.com/episode/breathwork-for-health-focus-and-stress-relief

Liang, F., Marks, W. D., & Feldman, J. L. (2022). Circuitry underlying the control of sighing in mammals. Nature, 610(7933), 413–418. https://doi.org/10.1038/s41586-022-05200-5