The practice of covering one’s mouth while yawning is a widespread custom with roots stretching back over two millennia, stemming from a combination of health concerns, spiritual beliefs, and eventually, social etiquette.

Historical Background: The superstition’s origins can be traced to at least two distinct theories. The first, prevalent in earlier times, centered around the potential for transmitting fatal diseases through a yawn. As noted by the Italian historian Polydore Vergil in his 1499 work, De Rerum Inventoribus, yawning was linked to deadly plagues, leading people to protect themselves with the sign of the cross to ward off illness. Vergil mentions the custom of ‘crossynge of our mouth’ which aimed to provide a religious barrier against the potential spread of sickness.

Cultural Beliefs: Parallel to concerns about physical health were beliefs relating to the spiritual vulnerability experienced during a yawn. The ancient Greeks and the classical Maya believed that the act of yawning could allow spirits, either malevolent or benign, to enter or leave the body. One specific notion posited that the Devil instigated the yawn, creating an opening for demons to infiltrate the yawner’s body while their mouth was agape. Another perspective suggested that the soul itself might escape during a yawn, and covering the mouth was the only way to prevent its departure. This concern for the soul’s safety underscored the importance of physically guarding the mouth during this seemingly innocuous act.

Evolution of the Superstition: The belief that yawning was a dangerous act was seemingly supported by observations of newborn babies. Physicians in antiquity, attempting to understand infant mortality (estimated between 50-200 deaths per thousand births), noted that infants who did not survive often yawned excessively. This observation was interpreted by some as evidence that the infants’ souls were indeed escaping through their open mouths. Consequently, new mothers were advised to closely monitor their infants and physically cover their mouths whenever they yawned as a protective measure. Over time, these beliefs evolved and intertwined with burgeoning social norms.

Modern Interpretations: By the seventeenth century, these superstitious beliefs had merged with a growing sense of social decorum. Yawning was increasingly perceived as impolite, prompting individuals to conceal the act out of consideration for others. In 1663, Francis Hawkins, an English Jesuit and translator, advised against yawning openly and loudly, further solidifying the social stigma associated with the act. While modern science offers theories about yawning, primarily suggesting it’s a mechanism to increase oxygen intake when tired or bored, the exact reasons remain unclear. Despite these scientific explanations, the deeply ingrained habit of covering the mouth when yawning persists in many cultures, a testament to the enduring power of historical beliefs and social conventions.