The physiological sigh is a breathing pattern that the body performs naturally and that can also be done deliberately to calm the nervous system quickly. It consists of a double inhale through the nose, a normal full breath followed immediately by a second, shorter “top-up” inhale, and then a long, slow exhale through the mouth. The body does this spontaneously throughout the day, often without you noticing, and especially during sleep, crying, or moments of stress. Its physiological purpose is to reinflate the tiny air sacs in the lungs called alveoli, which can collapse over time, and to offload built-up carbon dioxide more efficiently. The two-stage inhale pops these collapsed sacs back open, improving the exchange of oxygen and carbon dioxide.

As a deliberate practice, the physiological sigh has drawn attention as one of the faster ways to downshift from a state of stress or anxiety in real time. The extended exhale is the key part for relaxation, because lengthening the out-breath stimulates the parasympathetic nervous system and slows the heart rate. Even one to three repetitions can produce a noticeable drop in physiological arousal, which is part of why it’s appealing as a quick, portable tool you can use anywhere without any preparation. The pattern was popularized in recent years through neuroscience research and science communicators, and a 2023 controlled study found that a few minutes of daily cyclic sighing improved mood and reduced respiratory rate, comparing favorably to other brief breathing practices and meditation. As with much of this research, the studies are still relatively small, but the mechanism is well understood and the technique carries essentially no risk.