Why do we sigh, and does sighing relieve stress?

A sigh is a breath with a job

In a 2016 paper in Nature, researchers at Stanford University School of Medicine and UCLA described sighs as long, deep breaths that also happen spontaneously during normal breathing, at a rate of several per hour in humans and dozens per hour in rodents.

The long-standing explanation is mechanical. During ordinary quiet breathing, some of the alveoli, the tiny air sacs where oxygen crosses into the blood, collapse. A periodic extra-large breath pops them open again. The same paper describes regular sighing as something that improves gas exchange and may help preserve lung integrity by reinflating collapsed alveoli.

The Nature study also found the switch for it, at least in mice. In the preBötzinger complex, the brainstem cluster that sets the rhythm of breathing, about 200 neurons respond to two signalling peptides. Blocking both of their receptors abolished sighing, and removing those neurons stopped sighs while leaving the rest of breathing intact, at least at first. That is animal work, but it suggests sighing is a regulated reflex rather than a habit.

Why sighs show up with feelings

The same reflex is clearly tied to mood. The Nature authors note that sighing increases with low oxygen, with stress, and in anxiety disorders and some other psychiatric conditions. But stress is not the whole story. In three experiments published in Psychophysiology in 2009, a team at the University of Leuven in Belgium exposed volunteers to a loud noise, or to the threat of one, and recorded their breathing. People sighed more when the threat ended than while it lasted. The sigh looked more like relief than tension.

A related Leuven study of 42 healthy people sitting quietly for 20 minutes found a pattern around each spontaneous sigh. In the breaths leading up to it, breathing became more irregular. After the sigh, it settled into a more orderly rhythm. The researchers called this the resetter hypothesis: a sigh may work as a reset button for the breathing system. In a 2018 follow-up, volunteers breathed against a resistance that made breathing feel harder, and they sighed more often at the moment the resistance was removed.

There is a social side too. A 2008 study by Karl Halvor Teigen at the University of Oslo found that people mostly link sighing to low-energy negative states. When others sigh, we read it as sadness; when we sigh ourselves, we tend to describe it as giving something up. In a puzzle task with no solution, participants sighed along with their failed attempts, which Teigen read as a pause before dropping one plan and trying another.

Does sighing on purpose relieve stress?

Here the evidence splits. A 2010 Leuven study in Physiology & Behavior measured muscle tension after a stressful mental task. A spontaneous sigh was followed by a drop in tension, consistent with relief. But when participants were told to take one deliberate sigh during recovery, they recovered less well, not better. A single forced sigh did not reproduce what a natural one seemed to do.

A paced practice is a different thing from one forced sigh. In 2023, a Stanford team published a randomized trial in Cell Reports Medicine that enrolled 108 adults and assigned them to five minutes a day, for about a month, of one of four practices: cyclic sighing (30 people), box breathing (21), cyclic hyperventilation with breath holds (33), or mindfulness meditation (24). All groups reported less anxiety and less negative mood. Cyclic sighing produced the largest daily rise in positive mood and the biggest drop in breathing rate, and both differences were statistically significant compared with meditation. Heart rate variability did not differ significantly between the groups.

The authors are open about the limits. The study ran remotely, so they could not control exactly how people practiced. It lasted four weeks with no follow-up, people with moderate to severe psychiatric or medical conditions were excluded, and the cyclic sighing arm had 30 people. On average, the breathing groups practiced a little under six minutes a day and completed about 20 of the 28 days. It is a promising early result, not proof that sighing treats stress or anxiety.

How the cyclic sighing in that study was done

If you are curious, this is how the Stanford participants were instructed, offered as a description of a research protocol rather than a prescription. They sat in a chair or lay down and set a timer for five minutes. They breathed in slowly, ideally through the nose, and when the lungs felt full, breathed in once more to top them up; the second inhale is usually shorter, and that is expected. Then they breathed out slowly and completely, ideally through the mouth, and repeated the pattern until the timer ended before returning to normal breathing.

The NHS describes a similar, gentler exercise for stress: breathe in through the nose and out through the mouth, gently and regularly, counting from one to five if it helps, for at least five minutes. It notes that you get the most benefit from doing it regularly, as part of a daily routine.

Common mistakes when reading about sighs

Treating one small trial as settled. The cyclic sighing result comes from 30 people practicing at home for a month. It needs repeating in larger, longer studies before anyone calls it a treatment.

Assuming any sigh will do. The Leuven work suggests a spontaneous sigh and a sigh on command are not the same event. The Stanford protocol was slow and paced over five minutes, not a few dramatic exhales in a row.

Ignoring sighs that come with breathlessness. Frequent sighing alongside a feeling that you cannot get enough air is a different situation from a sigh of relief, and it deserves a doctor's attention rather than a breathing trick.

When frequent sighing is worth a check

The Nature authors note that in anxiety disorders and other psychiatric conditions, sighing can become debilitating. The NHS says shortness of breath may be nothing to worry about but can be serious. Its advice is to call emergency services if you have severe difficulty breathing, your chest feels tight or heavy, pain spreads to your arms, back, neck or jaw, your lips or skin turn pale, blue or grey, or you become suddenly confused. It recommends seeing a doctor if breathlessness gets worse during normal activities or when lying down, and it warns against trying to self-diagnose the cause.

If you like the sigh as a small ritual rather than an exercise, Fogglass borrows it as a gesture: you press and hold to fog a window on your phone, draw through the fog with a finger, and watch the line cloud over again. It is a pastime, not a breathing program, and it makes no claim to calm anyone.

This article is general information, not medical advice. If your breathing feels wrong, talk to a doctor, and if you have severe difficulty breathing or chest pain, call your local emergency number. In the US, if you are in emotional crisis, you can call or text 988 to reach the 988 Suicide & Crisis Lifeline.

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