The Physiological Sigh: A 30-Second Breathing Exercise to Lower Stress 

• A physiological sigh is a simple breathing exercise, recently popularized, that can lower stress, improve your mood, and restore a feeling of calm.
• To perform the physiological sigh, take a deep inhale followed by a short second inhalation, and then an extended exhalation. Repeat one or two more times.
• If you’ve noticed your stress levels are rising in Oura’s Daytime Stress feature, try to practice a physiological sigh or another breathing exercise and watch how your body responds. 

You see your stress levels spike in the Oura App’s Daytime Stress feature. But you only have a couple minutes before your next meeting. What can you do to lower your stress? 

Sigh. 

No, really — how about a sigh? You’ve probably sighed several times today already without realizing it, as the average person sighs about once every five minutes.

But a certain type of voluntary sigh, called the physiological sigh, has been shown in recent research to be an effective way to alleviate stress quickly. This is called the physiological sigh. 

READ MORE: Track, Understand, and Manage Your Stress With Oura

What is the Physiological Sigh?

A sigh is defined as an involuntary deep breath, controlled by two small clusters of neurons in the brain stem. “A sigh starts out as a normal breath, but before you exhale, you take a second breath on top of it,” as UCLA neuroscientist Jack Feldman, PhD, explained in an interview. This is then followed by an extended exhalation.

The physiological sigh was discovered by scientists in the 1930s, but has recently been popularized as a way to lower stress by neuroscientist Andrew Huberman, PhD. “Physiological signs were discovered in the 1930s as a pattern of breathing that people go into spontaneously when they are in claustrophobic environments, or in deep sleep,” Huberman explains on his podcast.

He also notes that the physiological sigh is an excellent “in-the-moment” tool to combat stress. While there are powerful tools to combat stress like meditation, breathwork, good nutrition, good social connections, and avoiding all bad things in life, these types of tools require that people step away from the stress-inducing activity.

“By contrast, my lab and other laboratories have been very interested in developing tools that allow us to push back on stress… in real time, meaning without having to disengage from the stress-inducing activity,” Huberman says. “The best way that I am aware to do that is called the physiological sigh.”

The Science Behind the Physiological Sign 

The purpose of the sighing reflex is to protect your lungs. The delicate sacs in your lungs, called alveoli, can collapse, compromising the exchange of oxygen and carbon dioxide (CO2). That’s why every five minutes or so, sighing happens, to bring in twice the volume of a normal breath to inflate the alveoli.

You can leverage this reflex to combat stress. Stress causes a change in your breathing rate and pattern. As your sympathetic nervous system — aka your “fight or flight” response — starts to dominate, your breathing becomes fast and shallow.

When you deliberately alter your breathing pattern with a sign, it interrupts this threat system, overriding your sympathetic nervous system and helping you self-soothe.

READ MORE: How Stress Works: The Mind-Body Connection

How to Perform the Physiological Sigh

Based on Huberman’s technique outlined in his video (see below), here’s how you can perform the physiological sigh for stress relief.

1. Inhale deeply: Take a deep breath in through your nose, filling your lungs with air. Allow your diaphragm to expand as you breathe in.
2. Inhale again: Take a second breath – it will be shorter and your diaphragm won’t expand as much.
3. Exhale completely: Release the air through your mouth.

Repeat for two or three more times. 

Here’s a video from Huberman to see it in action:

The Benefits of a Physiological Sigh

Performing a series of physiological sighs lowers your stress arousal in real-time, you may feel immediately calmer and more clear-headed as you breathe more deeply and slow your respiratory rate down.

Last year, a randomized controlled trial led by Huberman and colleagues was published in Cell Reports Medicine comparing the efficacy of controlled breathing exercises for stress.

In the study, just over 100 participants were split into four groups and asked to perform five minutes a day of one of the following four practices: the physiological sigh, box breathing, cyclic hyperventilation, or mindfulness meditation (for a control).

The result: All four groups reported a reduction in their anxiety, an improvement in their mood, and reduced physiological arousal (a lower heart rate and improved HRV).

However, physiological sighing came out on top as the most effective practice. It led to the greatest improvement in the participants’ moods and the greatest reduction in their breathing rate.

Here are four reasons why physiological sighing is so effective for stress management.

1. It lowers your breathing rate quickly.

During times of stress, the sympathetic nervous system takes over. This causes an involuntary chain of physiological responses, including rapid and shallow breathing (hyperventilation). This can exacerbate stress sensations and reduce blood flow to your brain.

The quicker you can slow your breathing rate, the better. In fact, Huberman’s study found that cyclic sighing improved the participant’s baseline respiratory rate over the course of the study.

READ MORE: Understanding Your Respiratory Rate While Sleeping

2. It regulates CO2 levels, which can help balance your emotions.

There’s a link between different emotional states and breathing patterns. According to research, too much or too little CO2 in the body can trigger feelings of anxiety, fear, and panic. When you breathe rapidly in response to stress, you disrupt the balance of CO2 and oxygen in your body – and are likely to feel the effects of this on your emotions.

Regulating and slowing down your breath, on the other hand, regulates your CO2 levels and improves your mood.

3. Deep breathing activates the parasympathetic nervous system.

The double inhale of a physiological sigh increases the depth of your inhalation, followed by an extended exhalation. This is particularly effective for combatting stress.

As noted in Huberman’s study: the extended exhalations of sighing activate the parasympathetic nervous system by increasing vagal tone. It triggers the release of neurotransmitters like acetylcholine, which in turn promotes various physiological responses like higher HRV, and an overall calming effect on the body.

When you cyclically sigh with an extended exhale, you deliberately override the fast shallow breathing pattern characteristic of the fight or flight response. In other words: You put yourself back in the driver’s seat, rather than being driven away by stress.

4. It’s easy and simple to do – which helps you stay consistent.

When a habit is easy to adopt with fewer barriers to entry, people tend to be more consistent, establishing a routine that becomes ingrained over time. As Oura’s behavioral scientist Sofia Strömmer, PhD, says, “When you’re trying to start a new habit, the easier it is, the better.” 

“Some of our members have already told us that they can see their Daytime Stress lower (indicating that they are less stressed) in response to short breathing exercises,” says Strömmer. Seeing this positive change in real-time data is a motivating way to keep up the habit!

When five-minute breathing exercises become an established response to stress, you might start to notice an increase in your resilience to stress. Stress resilience refers to how effectively you can bounce back from stress – and that all depends on having the right tools at your disposal.

RELATED: Resilience: Improve Your Ability to Recover From Stress

About the Oura Expert

Sofia Strömmer, PhD, is a behavioral scientist at Oura. She is from Finland, but lived in the UK for 16 years before moving back to join Oura. She is a Chartered Psychologist and has a PhD in Psychology focusing on the motivational determinants of exercise behavior. Her area of expertise is in motivational aspects of health behavior change and how motivation for health behaviors arises and is maintained. Before joining Oura, Sofia worked as a researcher at the Medical Research Council at the University of Southampton.