The physiological sigh: two breaths in, one long breath out

How to do a physiological sigh

1. Sit or lie down comfortably and let your shoulders drop.
2. Breathe in through your nose until your lungs feel full.
3. Without breathing out, sneak in a second, shorter inhale through your nose. It’s smaller than the first one, and that’s how it should be.
4. Breathe out slowly and all the way, through your mouth or your nose. The exhale takes clearly longer than both inhales together.
5. One to three sighs are enough in the moment. Then go back to breathing normally.

That’s also how the Stanford researchers taught it: two inhales through the nose, a slow exhale through the mouth. People who preferred to breathe only through the nose were allowed to.¹

Six sighs, one minute

Tap Breathe along when you’re ready

Breathe along

What happens in your body

Nobody invented sighing. Your body does it on its own: every few minutes, the breathing center in your brainstem slips in a deeper breath. These spontaneous sighs reinflate the alveoli, the tiny air sacs in your lungs. We sigh more under stress and when oxygen runs low.² In mice, researchers have found the circuit behind it: about 200 nerve cells in the breathing rhythm generator that turn normal breaths into sighs.²

A sigh also seems to tidy up your breathing. In 42 healthy adults sitting quietly, breathing became more and more irregular before a spontaneous sigh and more orderly after it.³ The research team proposes that a sigh works like a reset button for both breathing and emotions, which is why it brings relief.⁴

1. Calm breathing: small, even breaths.
2. The first inhale through the nose, deeper than usual.
3. A second, short inhale on top, until your lungs are completely full.
4. A long, slow exhale until your lungs are back at rest.
5. Your heart beats slightly faster as you breathe in and slightly slower as you breathe out. A long exhale gives the slower part more time.

Watch again

The second half of the exercise is the long exhale. Your heart speeding up slightly as you breathe in and slowing slightly as you breathe out is completely normal. It’s called respiratory sinus arrhythmia.⁵ In a lab study with 30 adults, people felt more relaxed when they breathed out longer than they breathed in, regardless of whether they breathed fast or slow.⁶

You’ll often read that the double inhale pops open collapsed air sacs so you can offload more carbon dioxide. That’s a plausible idea, but it hasn’t been tested directly for the deliberate exercise. What’s been studied is the exercise as a whole, not that explanation.

What the Stanford study found, and what it didn’t

The best-known study comes from Stanford University and was published in 2023.¹ 108 healthy adults practiced for five minutes every day for a month. They were randomly assigned to one of four groups:

All four groups felt less anxious and less down after their daily session, and by similar amounts. For positive mood, the breathing exercises came out ahead. But only cyclic sighing beat meditation by a statistically clear margin, and its lead grew the more days people practiced. Cyclic sighing also lowered the breathing rate measured daily by a wrist tracker more than meditation did. Resting heart rate, heart rate variability and sleep didn’t change meaningfully in any group.¹ The study tested the technique, not the nowa app.

The study has limits, and the researchers name them. It ran online, with nobody watching people practice. On average, participants practiced on just under 20 of 28 days. It was designed as a pilot for a larger trial, and each group was small. People with heart disease, seizures, glaucoma, pregnancy or certain mental health conditions weren’t included.¹

What newer research adds

Since 2025, two smaller studies have tested the sigh in real-world settings:

• In tense everyday moments: 47 students did one minute of cyclic sighing, one minute of box breathing, or nothing when they felt tense. Both breathing exercises lowered in-the-moment anxious feelings more than doing nothing. Reaction times on an attention test were a bit slower afterward, though.⁷
• After an all-out workout: in 62 military cadets, the calming branch of the nervous system bounced back faster with sighing or box breathing than with normal breathing, measured by heart rate variability. Heart rate dropped about equally fast in all groups.⁸

Both are small studies. They point in the same direction but don’t prove that the sigh beats other slow breathing exercises. In both, box breathing did about as well.

Is it really the fastest way to calm down?

That claim goes further than the evidence. The studies above compare the sigh with a handful of other exercises, not with every way people calm down, and box breathing often kept up. What the research does support is more modest: a meta-analysis of 12 randomized trials with 785 adults found that breathing exercises lower stress by a small to moderate amount on average, and its authors explicitly warn against letting hype run ahead of the evidence.⁹

When it fits, and when something else might be better

The sigh is short and easy to hide. It fits the moments when things get tight: before a hard conversation, after a scare, when your head is too full, while you’re stuck in traffic or in line. You can do it sitting, lying down or standing.

For a longer break or for bedtime, exercises that slow your breathing down over several minutes are often a better fit, such as coherent breathing or these breathing exercises for sleep.

Common mistakes

• Too many sighs, too fast. If you feel dizzy or notice tingling in your hands or lips, you’re probably breathing too much. Exhale slowly, take a break after a few sighs and breathe normally.
• Breathing out between the two inhales. The second inhale goes on top, with no pause and no exhale in between.
• Lifting your shoulders. Let the breath go into your belly and sides, and keep your shoulders down.
• Pushing the air out. Just let it flow out, like a sigh of relief.

Frequently asked questions

How many physiological sighs should I do?

One to three are enough in the moment. In the Stanford study, people did five minutes a day in a row. If you get dizzy, you’re doing too many too quickly.

Should I breathe through my nose or my mouth?

In through the nose and out through the mouth, as in the study. Nose only works, too.¹

Physiological sigh or box breathing?

Both did well in the studies so far. The sigh is quicker and easier to do on the spot, while box breathing has more structure and holds. Try both and keep the one that feels better. Box breathing is free in nowa, too.

Is a physiological sigh the same as cyclic sighing?

Almost. A physiological sigh is a single double inhale with a long exhale. Cyclic sighing means repeating it for several minutes, as in the studies.

Does it help you fall asleep?

That hasn’t been tested directly. In the Stanford study, the sleep data from the wrist tracker didn’t change in any group.¹ For falling asleep, slow exercises over several minutes are a more natural fit.