Physiological Sigh: How to Do It and Does It Reduce Stress?

A physiological sigh is two inhales through the nose (one deep, one short top-up) followed by a long, slow exhale. In a 2023 randomized trial, practicing it for 5 minutes a day for a month improved mood and lowered breathing rate more than mindfulness meditation. Wider reviews suggest breathwork has a real but modest effect on stress.

This page is general information, not medical advice. If anxiety is persistent or interferes with daily life, speak with a qualified clinician.

What the physiological sigh is

Sighs are not only emotional. Your lungs produce them on their own every few minutes. A 2016 Nature study from the Krasnow and Feldman labs found that spontaneous sighs help reinflate the lungs’ tiny air sacs (alveoli). The same study traced sighing in mice to a small group of peptide-releasing neurons that signal the brainstem’s breathing rhythm generator. That work explains where sighs come from. It did not test sighing as a way to calm down.

On the Huberman Lab episode “Tools for Managing Stress & Anxiety”, Andrew Huberman describes doing a sigh on purpose, a double inhale followed by a long exhale, as a real-time calming tool, and ranks it as the fastest way to reduce stress in the moment. That ranking is his claim. No study has compared it head-to-head against every other technique.

How to do it

• Inhale: breathe in deeply through the nose.
• Top up: add a second, shorter inhale to fill the lungs fully. It is normal for the second inhale to be smaller.
• Exhale: breathe out slowly and completely, ideally through the mouth, until the lungs feel empty.
• In the moment: Huberman suggests one to three sighs. Heart rate takes a little while to settle, so expect a gradual change rather than an instant one.
• As a practice: the Stanford trial asked people to repeat the pattern for 5 minutes a day, seated or lying down.

Nose-in, mouth-out is the usual form, but the trial told participants they could breathe entirely through the nose if they preferred.

Why exhale-focused breathing may calm you

Your heart rate rises a little when you breathe in and falls when you breathe out. This normal rhythm is called respiratory sinus arrhythmia. A review in Chest describes it as part of the way breathing and circulation are coordinated. Making the exhale longer than the inhale gives the slowing phase more time, which is the basic idea behind exhale-focused breathing. A systematic review of slow breathing linked slow breathing to higher heart rate variability, more parasympathetic (rest-and-digest) activity, and calmer emotional reports.

On the podcast, Huberman gives a more detailed mechanical explanation involving heart volume and blood-flow sensing. Physiology reviews describe the effect mainly as vagal-nerve modulation of heart rate, so treat his version as a simplification.

What the research says

The main trial. Balban and colleagues (2023) randomly assigned 108 adults, mostly Stanford undergraduates, to 5 minutes a day of one of four practices for a month:

• cyclic sighing
• box breathing
• cyclic hyperventilation with breath holds
• mindfulness meditation

Breathwork overall, and especially cyclic sighing, produced greater improvement in mood and a larger drop in resting respiratory rate than meditation. The authors concluded: “Daily 5-min cyclic sighing has promise as an effective stress management exercise.”

Some limits of that trial:

• Huberman was the lead contact author, so the podcast is promoting a study he co-led.
• Physiology was tracked with WHOOP wearables, which participants kept as their reward for taking part.
• The sample was small and mostly students.
• Data were collected remotely during the pandemic.
• It tested a daily routine, not one to three sighs in a stressful moment.

The bigger picture. A 2023 meta-analysis of 12 randomized trials with 785 adults found breathwork lowered self-reported stress with a small-to-medium effect (g = −0.35). Most included studies had a moderate risk of bias, and the authors cautioned against “a miscalibration between hype and evidence.” Breathing techniques look useful, but they are not a substitute for treatment of anxiety disorders.

The four protocols compared

Source: Balban et al., 2023. The headline comparison is breathwork, and especially cyclic sighing, against meditation; treat any ranking among the other three as unsettled.

Why a sigh might act as a reset

A review in Biological Psychology proposed a psychophysiological reset model. In it, sighing “is hypothesized to function as a resetter in the regulation of both breathing and emotions,” restoring balance in breathing variability and bringing relief. It is a model, not a trial result, but it offers a mechanism that fits both the Nature sigh-circuit work and the Stanford findings.

Exhale-focused vs fast breathing

Not all breathwork is calming. Huberman notes that breathing patterns that stress the inhale tend to raise alertness, while those that stress the exhale tend to calm. Fast, repeated breathing with breath holds (often called Wim Hof or tummo style) deliberately triggers an adrenaline response. That style is covered on our short-term vs chronic stress page, together with its safety warnings. If your goal is to wind down for bed, the complete guide to better sleep covers routines with stronger evidence.

Practical notes

• Try a few sighs before a stressful call or presentation, and note how you feel.
• If you want a habit, 5 minutes a day matches what the Stanford trial tested.
• Stop if you feel lightheaded. People with lung or heart conditions should check with a clinician first.
• Breathing is one tool alongside sleep, exercise and social connection. For stress-related supplements, see L-theanine for stress. For the wider focus toolkit, see the focus and cognition guide.

For a longer guided rest, see non-sleep deep rest (NSDR).