Most of us sigh without thinking about it.
You might sigh after a stressful phone call, when you sit down after a long day, when you’re frustrated, or simply when you’ve been concentrating for a while. Sometimes you don’t even realise you’ve done it.
Interestingly, sighing is a normal part of how the respiratory system works. Your brain actually generates spontaneous sighs throughout the day, and they serve a useful physiological purpose.
A sigh is essentially a larger-than-normal breath, usually involving a deeper inhalation followed by an exhalation. Research has shown that spontaneous sighing helps keep the tiny air sacs in the lungs, called alveoli, functioning properly.
Sighing helps reset the lungs
Your lungs contain millions of tiny alveoli where oxygen enters the blood and carbon dioxide leaves it. Some of these air sacs can gradually become less inflated, particularly when we take shallow breaths for extended periods.
A sigh provides a larger breath that helps reopen these areas.
Think of it a little like stretching the lungs. A normal breath may not fully expand every part of the respiratory system, whereas a sigh gives the lungs a bigger movement.
This is one reason sighing happens automatically. Your brain periodically triggers these deeper breaths without you having to consciously decide to do it.
Why do we sigh when we're stressed?
There’s another interesting connection between sighing and stress.
When we're under pressure, our breathing can change. We may start breathing faster, holding our breath intermittently, or taking smaller, shallower breaths. This can happen while we're working at a computer, driving, competing, having a difficult conversation, or simply worrying about something.
A deliberate sigh can interrupt that breathing pattern.
One particularly interesting type is the physiological sigh: two consecutive inhalations followed by a long exhalation.
The first inhale is relatively normal. The second, smaller inhale helps inflate areas of the lungs that may have become underinflated. The long exhale then helps empty the lungs.
Research from Stanford and other laboratories has looked at this type of breathing and found that repeated physiological sighs can influence both breathing patterns and subjective stress levels.
The long exhalation is important here.
When you extend the exhale, you generally slow the breathing cycle and give your body a little more time between inhalations. This can be useful when you've become tense and your breathing has become rapid or erratic.
There’s also a carbon dioxide connection
Breathing has a constant relationship with carbon dioxide.
We often think of breathing primarily as a way of getting oxygen into the body, but carbon dioxide is equally important. The amount of CO₂ in your blood influences breathing rate, blood pH and how strongly your brain signals you to breathe.
During stress, breathing can become faster than the body's actual metabolic needs require. If you continue breathing rapidly, you can remove CO₂ faster than your body is producing it.
A slow, controlled breath can help bring the breathing pattern back towards a more appropriate level.
This is one reason breathing exercises can feel surprisingly effective when you're tense. You're directly influencing a system that is constantly communicating with the brain.
Why does a sigh sometimes feel so good?
There’s a reason people often describe a big sigh as a feeling of release.
After holding tension or concentrating for a long time, a deeper breath followed by a slow exhale can change the rhythm of your breathing almost immediately.
You may notice your shoulders drop. Your jaw may relax. Your breathing may become quieter. You may simply feel that you have more space to breathe.
And sometimes, your body does this completely by itself.
That spontaneous sigh may be your respiratory system adjusting your breathing pattern and maintaining healthy lung function.
Try it yourself
The next time you notice yourself feeling tense, try a physiological sigh.
Take a normal breath in through your nose.
Then take a second, smaller inhale on top of it.
Follow that with a slow, relaxed exhale through the mouth.
You don't need to force a huge breath or repeat it twenty times. One or two sighs may be enough to interrupt a tense breathing pattern.
Then return to normal breathing and notice what has changed.
Sighing is a simple example of how closely breathing, the lungs and the brain are connected. Something as ordinary as a spontaneous sigh has a surprisingly sophisticated job to do.
And sometimes your body knows exactly when it needs one.
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