Sneezing, a sudden and forceful expulsion of air from the lungs through the nose and mouth, is a reflexive response to irritants in the nasal passages. Typically, when awake, any foreign particle or excessive mucus detected by the nasal mucosa triggers a reflex that is sent to the brain, specifically to a region called the medulla. The brain then responds by organizing a complex series of actions that results in a sneeze, expelling the irritants from the nasal cavity.
However, when people are asleep, the body enters a state of muscle relaxation due to a decrease in neurotransmitter activity that reduces overall bodily responses to stimuli, including those that would otherwise trigger a sneeze. The sneeze reflex pathways in the brain are less reactive due to the decreased level of cortical control during sleep. This means that even if irritants are present in the nasal passages, the reflex is not activated the way it is when you are awake.
Additionally, during the rapid eye movement (REM) stage of sleep, most of the body’s voluntary muscles are paralyzed, including those involved in the mechanism of sneezing, as a means of preventing the body from acting out dreams. This paralysis contributes to the suppression of many reflexes, including the sneeze reflex. Thus, even if the nerves that facilitate sneezing were active, the body's inability to execute the physical action of a sneeze due to muscle paralysis would still prevent sneezing during REM sleep.
Despite this general cessation of sneezing during sleep, some people might wake up from sleep in order to sneeze. This interruption of sleep usually occurs if the nasal irritants are sufficient to break the threshold of the decreased sneeze reflex sensitivity, potentially combined with a shift out of the REM stage, wherein muscle tone begins to return to the body.
Understanding this functionality is not only interesting but also beneficial as it illustrates one of the many ways our bodies work to achieve restful and uninterrupted sleep, essential for overall health and well-being.
