A sigh is an audible exhalation of breath—a groan, an expression of sadness, grief, yearning, resignation, or frustration. Why do we sigh?
Usually, a negative mood motivates a sigh, though sighs can also be a simple expression of relief. When we have negative emotions, our brain may trigger the release of “sigh neuropeptides” that cause us to sigh. Scientists suggest that a sigh might serve as a “reset button” for the respiratory system.