What Is the Physiological Sigh?
The physiological sigh is a breathing pattern of two quick inhales through your nose followed by one long, slow exhale through your mouth. It uses your body’s natural sigh reflex to calm the stress response faster than a single normal breath. Researchers at Stanford also call the repeated version of this pattern “cyclic sighing,” and it’s one of the few breathwork techniques that has been directly tested in a peer-reviewed randomized study.
This article covers how to do it, what the Stanford research actually found, how it compares to other breathing techniques like box breathing, and who should be careful before trying it.
How to Do a Physiological Sigh
- Inhale through your nose until your lungs feel comfortably full
- Without exhaling, take a second short “top-up” inhale through your nose
- Exhale slowly and completely through your mouth
- Repeat 1 to 3 times for in-the-moment stress, or continue for a few minutes for a longer practice
The double inhale is the key difference between this and other slow-breathing techniques. It’s meant to briefly reopen small air sacs in the lungs before the long exhale that follows.
What the Stanford Research Actually Found
The main evidence for this technique comes from a 2023 study published in the peer-reviewed journal Cell Reports Medicine by researchers at Stanford University, including neurobiologist Andrew Huberman and psychiatrist David Spiegel. The study randomly assigned about 100 adults to one of four daily 5-minute practices for one month: cyclic sighing (repeated physiological sighs), box breathing, cyclic hyperventilation with breath retention, or mindfulness meditation as a comparison group.
All four groups reported improved mood and reduced physiological arousal by the end of the month. Cyclic sighing showed the largest improvement in mood and the biggest drop in resting breathing rate compared with meditation. The exhale-focused pattern outperformed the inhale-focused pattern (cyclic hyperventilation) on these measures.
This aligns with the broader category of relaxation techniques that groups like the National Center for Complementary and Integrative Health (NCCIH) have studied for decades, which generally link slow, controlled breathing to lower heart rate and blood pressure by activating the body’s relaxation response.
Why the Long Exhale Matters
Your autonomic nervous system runs two main modes: the sympathetic branch (fight-or-flight, which speeds up heart rate and breathing) and the parasympathetic branch (rest-and-digest, which slows things down). Extending your exhale is thought to shift activity toward the parasympathetic branch, partly through increased vagus nerve activity, the main nerve connecting the brain to the heart, lungs, and gut. This is the same general mechanism behind other slow-exhale breathing techniques, not something unique to the physiological sigh.
Physiological Sigh vs. Other Breathing Techniques
- Physiological sigh (cyclic sighing): Double inhale, long exhale. In the Stanford study, this produced the largest improvements in mood and the largest reductions in respiratory rate among the techniques tested. Works in as little as 1 to 3 breaths for in-the-moment calm.
- Box breathing: Four equal phases — inhale, hold, exhale, hold — each for the same count. Often used for focus and steadiness rather than fast stress relief. Read more in our box breathing and 4-7-8 breathing guide.
- Cyclic hyperventilation with retention: Emphasizes a longer, deeper inhale followed by a breath hold. In the same Stanford study, this group showed smaller mood benefits than the sighing group.
- Mindfulness meditation: Passive observation of the breath without controlling it. All groups in the study improved, but meditation showed a smaller mood boost than the breathwork techniques over the month.
When to Use It
Based on how the research was designed, there are two different ways to use this technique:
- In-the-moment stress: A few physiological sighs (1 to 3 breaths) may help you feel calmer within about 30 seconds, though this specific quick-dose use was not the main outcome tested in the Stanford trial.
- Daily practice: The study’s main results are based on 5 minutes of cyclic sighing per day for 28 days, which is the routine most directly supported by the data.
Evidence Limits
This is encouraging early research, but it has real limits worth knowing before you treat it as a proven fix:
- The key study included roughly 100 participants — a modest sample size for drawing firm conclusions
- It is one randomized trial; results have not yet been widely replicated by other research teams
- Mood outcomes were based on participant-reported questionnaires, not objective medical measures
- The study ran for one month, so it doesn’t tell us about effects over a longer period
- It measured mood and physiological arousal, not treatment of diagnosed anxiety disorders or other medical conditions
Who Should Be Extra Careful
Slow-breathing techniques are generally considered safe for healthy adults. However, the double-inhale and breath control involved can feel uncomfortable for people with respiratory conditions like asthma or COPD. As with other breath-holding or controlled-breathing practices, there have been rare reports that certain techniques may trigger symptoms in people with epilepsy, some psychiatric conditions, or a history of trauma.
If you’re pregnant, have a diagnosed health condition, or feel dizzy, lightheaded, or unusually anxious while practicing, stop and talk with a healthcare provider before continuing. This technique is not a replacement for treatment of an anxiety disorder, high blood pressure, or any other diagnosed condition.
A Simple Way to Try It
- Sit or stand somewhere you can breathe through your nose comfortably
- Try 1 to 3 physiological sighs the next time you feel stressed and notice how you feel afterward
- If you want to try the daily practice from the Stanford study, set aside 5 minutes once a day
- Keep your shoulders relaxed and let the exhale be slow, not forced
- Stop and check in with a healthcare provider if anything feels off, especially breath-holding discomfort
Frequently Asked Questions
Is the physiological sigh actually backed by research?
Yes, more directly than many breathwork trends. It was the specific technique tested as “cyclic sighing” in a 2023 randomized study published in Cell Reports Medicine by Stanford researchers, and it outperformed box breathing, cyclic hyperventilation, and mindfulness meditation on mood and respiratory rate in that trial.
How is this different from just taking a deep breath?
The double inhale is the distinguishing feature. The first inhale fills the lungs, and the second short “top-up” inhale is thought to briefly reopen small air sacs before the long exhale. A single deep breath doesn’t include this second inhale.
Can it replace anxiety medication or therapy?
No. The research shows improvements in mood and physiological arousal in generally healthy adults, not evidence that it treats diagnosed anxiety disorders. Don’t start, stop, or change any treatment without talking to a qualified healthcare provider.
How often should I practice it?
The Stanford study tested 5 minutes daily for 28 days for its main results. For quick, in-the-moment stress, 1 to 3 sighs is the commonly described dose, though that specific short use wasn’t the primary focus of the trial.
Related Reading on Make Time For Wellness
- Breathwork for Stress: Box Breathing, 4-7-8 and What Research Supports
- Progressive Muscle Relaxation: Technique, Sleep Applications and Evidence
- Stress and Sleep: How Worry Disrupts Rest and What Evidence-Based Steps Can Help
- Beginner Meditation: What Evidence Supports and Realistic Expectations
Educational Disclaimer
This article is for general educational purposes only and is not medical advice. It does not diagnose, treat, or promise to relieve any condition, and it should not replace guidance from a qualified healthcare provider. If you have a health condition, are pregnant, or experience worsening anxiety, dizziness, or other unusual symptoms while trying breathing exercises, stop and consult a healthcare professional.
Make Time For Wellness shares evidence-informed lifestyle and wellness guidance — not medical advice. We’re wellness educators, not doctors. For anything clinical or personal, please talk to a qualified healthcare provider. See our medical disclaimer.