Emotions and breathing have historically been associated in both animal and human studies. More recent research has shown that a number of respiratory characteristics (speed of breathing, depth, etc.) can vary based on emotional experience. The sigh (a distinct deep breath) is a specific form of respiratory action that is expressed during both positive and negative emotional states, such as those of contentment and frustration, respectively. However, the motivations for sighing have only recently come under examination, and little research has been conducted on the physiological and psychological aspects of the action.

A 2016 study by Elke Vlemincx, Ilse Van Diest, Omer Van den Bergh from the University of Leuven in Belgium investigated the potential effects of sighing on both systems.

“We have proposed that a sigh serves as a psychophysiological resetter, restoring homeostasis both physiologically and psychologically when a homeostatic balance has been compromised,” the researchers said.

Published online in Physiology & Behavior, the described experiment included 34 participants (17 female). They first completed a survey designed to measure trait anxiety, and were then fitted with electrodes and other equipment necessary to track respiration and physiological measures of anxiety/relaxation (skin conductivity, muscle tension, CO2 concentration).

Each subject took part in three different session blocks. No breathing instructions were given in the first block, while the following two included either deep breath (sighing) prompts or breath holding (not sighing) instructions. Instances of spontaneous sighing were also recorded for the instructed sigh group. Relief was self-reported continuously throughout all trials.

Statistical analyses of biological and psychological measures revealed two significant effects of sighing. Reported relief increased in the five seconds following sighs, but not after breath holding or without instructions. Muscle tension decreased moderately in the post-sigh measurement period, signifying a reduction in anxiety and/or increased relaxation.

They also examined differences between subjects who measured high and low in trait anxiety, and discovered that instructed breath holding actually produced minor but significant improvements in self-relief reports, but only in the low anxiety group. Oddly, this group also displayed slight increases in muscle tension after instructed sighs, despite reporting relief.

The act of sighing, both intentionally and spontaneously, appears to induce signs of relaxation in low-anxiety people as well as those with high trait anxiety, but the motivation for sighing can have an impact on the types of benefits experienced. Instructed deep breaths resulted in a similar level of psychological relief as spontaneous sighs, but physiological stress was negatively impacted in those with low-anxiety levels.

This finding may be a result of increased tension in response to the failure of instructed sighing to initially induce physical relaxation, but further research will be needed to uncover any supporting mechanisms. In total, this research demonstrates that sighing can be beneficial and possibly restorative to both psychological and physiological processes in terms of relaxation/anxiety.

“This study is the first to demonstrate that an instructed deep breath increases subjective relief,” the researchers said. “In addition, a spontaneous sigh decreases physiological tension in anxiety sensitive persons specifically.”