Physiological sigh

What the sigh is and why the body does it

Sighs are long, deep breaths with which we express sadness, relief or exhaustion. But they also occur spontaneously every few minutes without any emotion at all, to reopen collapsed air sacs in the lungs. They become more frequent with oxygen deficiency and stress. In 2016, a research group found the switching point in the brainstem of mice: small groups of neurons that, via two messenger substances from the family of bombesin peptides, control the respiratory rhythm generator and turn normal breaths into sighs.

In humans, it was mainly the research group around Vlemincx that studied what sighs do. Their thesis: a sigh is a reset that brings a stuck breathing pattern back into balance and triggers relief. In the laboratory, the sigh rate rose exactly when an unpleasant situation ended, and after a guided deep breath, participants reported more relief than before. In anxiety-prone people, muscle tension also decreased after a spontaneous sigh.

What the exercise makes of it

Cyclic sighing repeats this pattern deliberately: breathe in until the lungs feel full, add a second, shorter breath on top, then breathe out slowly and completely. The emphasis is on the long exhalation. The Stanford study compared this with two other breathing patterns: box breathing with equally long inhalation and exhalation and holding, and cyclic hyperventilation with breath retention, a pattern similar to Wim Hof breathing. Mindfulness meditation with passive observation of the breath served as the comparison.

What the studies show

Stanford study, Cell Reports Medicine 2023

Randomized remote study in summer 2020 with 108 participants, predominantly students in a psychology course: 30 practiced cyclic sighing, 21 box breathing, 33 cyclic hyperventilation with breath retention, 24 mindfulness meditation, each five minutes daily for 28 days. All groups became calmer and less anxious after the exercise. Positive mood rose per practice day by an average of 1.89 points in the sighing group and by 1.22 in the meditation group, and only for sighing was the difference from meditation significant. For state anxiety and negative mood, there was no difference between breathing exercise and meditation, and for sleep no change in any group. The resting breathing rate fell more under sighing, resting heart rate and heart rate variability did not. The study was designed as a pilot study and was registered only retrospectively; a co-author became an advisor in 2022 to the manufacturer of the measurement wristbands used.

One minute in everyday life, 2026

Preregistered pilot study with 47 students: in an acutely stressful situation, they did one minute of box breathing, one minute of cyclic sighing, or nothing. Both breathing exercises lowered state anxiety more than the control condition. Box breathing additionally led to fewer errors in an attention test, but both exercises led to longer reaction times.

Four minutes in the waiting room, 2025

Randomized pilot study in the X-ray waiting area of an orthopedic outpatient clinic: four minutes of guided cyclic sighing versus information of equal duration on dealing with the injury. The sighing group reported less pain intensity and less pain unpleasantness. Anxiety and depressiveness did not differ.

Meta-analysis on breathing exercises, 2023

12 randomized trials with 785 adults, mostly with a moderate risk of bias. Breathing exercises lowered self-reported stress with an effect size of −0.35, anxiety with −0.32 and depressiveness with −0.40. The authors explicitly warn that enthusiasm and evidence are diverging. The analysis contains no data specifically on sighing.

Sighs and relief in the laboratory, 2016 and 2017

In an experiment with uncertain and then resolved picture stimuli, participants reported more relief after a guided deep breath than before; in anxiety-prone individuals, tension in the forehead muscle decreased after a spontaneous sigh. In a second experiment with 29 healthy people, participants sighed more often during the transition to a safely pleasant situation than in the comparison phases, and in anxiety-prone individuals more sighs were associated with a steeper drop in cortisol.

What users report

At the end of the Stanford study, participants filled in a voluntary questionnaire, analyzed for all four groups together. 90 percent reported positive experiences during the exercises, 10 percent negative ones. 96 percent found the video instructions easy or fairly easy, 74 percent the exercises themselves. On average, the breathing groups practiced on just under 20 of the 28 days.

Where the data stop

The popularity rests essentially on one study with 30 people in the sighing group, predominantly young students, without preregistration and with a four-week duration without follow-up. The authors themselves write that the groups were too small to reliably compare the breathing exercises with each other, and that the remote study did not control how exactly people practiced. Against anxiety, sighing was no better than meditation, and nothing changed in sleep.

The two follow-up studies are pilot studies with short measurement immediately after the exercise. That the sigh is the fastest way to calm has not been tested against other methods by anyone; in the everyday study, box breathing lowered anxiety as well. For anxiety disorders, high blood pressure or heart rate variability as a treatment goal, there are no data.

How to do it

Sit or lie down. Breathe in through the nose until the lungs feel full, and add a second, shorter breath on top; that the second one is shorter is normal. Then breathe out slowly and completely through the mouth. That is one round. In the Stanford study, this was repeated for five minutes at a stretch, after which participants breathed normally again. If exhaling through the mouth does not suit you, you may breathe entirely through the nose; this was explicitly allowed in the protocol. More on breathing through the nose is on the page on nasal breathing.

For the acute moment, one minute was already enough in the everyday study; in the waiting room it was four. The effect on mood grew in the Stanford study with the number of practice days, so regular practice pays off more than occasional practice. Unlike Wim Hof breathing or CO2 tolerance training, this exercise does not involve holding the breath. If you feel dizzy, breathe more slowly or stop.

Safety

Cyclic sighing is a natural breathing pattern without breath holding. Systematically collected side-effect data nevertheless do not exist. The Stanford study excluded pregnant women as well as people with heart disease, a history of seizures, glaucoma, psychoses, bipolar disorder, addiction or suicidal thoughts, so data are missing for these groups. In the final survey, 10 percent across all groups reported negative experiences with the exercises.

Sources

• Stanford study on cyclic sighing — Balban et al., Cell Reports Medicine 2023, randomized, 108 participants
• Trial registry ClinicalTrials.gov NCT05304000 — protocol, groups and exclusion criteria of the Stanford study
• One minute of sighing or box breathing in everyday life — Riedl et al., Anxiety, Stress, & Coping 2026, 47 students
• Cyclic sighing in the waiting room against pain — Hanley et al., Journal of Behavioral Medicine 2025, randomized pilot study
• Meta-analysis on breathing exercises and stress — Fincham et al., Scientific Reports 2023, 12 studies, 785 participants
• The control of sighing in the brainstem, mice — Li et al., Nature 2016
• Sighs as a reset of breathing, review model — Vlemincx et al., Biological Psychology 2013
• Relief through deep breaths — Vlemincx, Van Diest, Van den Bergh, Physiology & Behavior 2016
• Sigh rate during relief and cortisol — Vlemincx, Meulders, Abelson, Biological Psychology 2017, 29 participants