The sneeze, medically known as sternutation, is a rapid, involuntary reflex action designed to forcefully expel irritants from the nasal passages. This protective mechanism begins with a sensation that signals the presence of an unwanted particle, triggering a complex chain reaction in the body.
The frustrating experience of feeling the intense urge to sneeze only for the sensation to vanish before completion is common. Understanding the mechanics of this reflex and the ways it can be interrupted offers insight into this physiological phenomenon.
The Physiology of the Sneeze Reflex
A successful sneeze is a coordinated, three-phase reflex arc orchestrated by the nervous system. It begins when an irritant, such as dust or pollen, stimulates the sensory nerve endings lining the nasal mucosa. These signals are then rapidly transmitted along the trigeminal nerve to the brainstem.
The brainstem houses the “sneeze center” within the medulla oblongata that processes the incoming signal. Once the irritation threshold is reached, this center initiates the motor phase of the reflex. This motor response involves a deep inhalation, followed by the coordinated contraction of numerous muscles to generate the explosive expulsion of air. This forceful blast is intended to clear the foreign substance from the airway.
Common Reasons for Interrupted Sneezes
The most frequent causes of a “stuck” sneeze are temporary and relate to the disruption of the reflex arc before the brainstem can execute the motor phase. One common reason is conscious or unconscious suppression, where a person deliberately tenses their facial or respiratory muscles to try and hold the sneeze back. This action interferes with the building physiological pressure required for the final expulsion, causing the urge to dissipate.
Another factor is a nerve distraction, which occurs when a person quickly shifts their focus to a different sensation. Pinching the nose or pressing the tongue hard against the roof of the mouth can introduce a new, competing sensory signal to the trigeminal nerve pathway. This secondary signal can effectively divert the brain’s attention, causing the original sneeze impulse to fade away.
The initial trigger itself might also be too weak or too fleeting to sustain the full reflex arc. If the irritant is quickly moved or neutralized by the nasal mucus, the sensory input to the brainstem ceases prematurely. Without continuous stimulation, the sneeze center does not receive the signal strength needed to launch the forceful clearing action.
Medical Conditions That Impair Sneezing
Chronic or underlying structural issues can severely inhibit the ability to sneeze, a condition sometimes referred to as asneezia. Structural deformities, such as a severely deviated nasal septum or the presence of nasal polyps, can prevent irritants from reaching the sensory nerves. These physical blockages mean the necessary trigger never makes contact with the nasal mucosa to initiate the reflex.
Neurological damage can directly impair the sneeze center in the brainstem. For instance, a lesion or stroke affecting the medulla oblongata can disrupt the transmission of signals, preventing the brain from executing the final, forceful expulsion. Even if the initial sensory urge is felt, the motor command is unable to be sent.
Certain systemic nervous system disorders can also interfere with the complex neural pathways that govern the sneeze reflex. Furthermore, surgical procedures carry a small risk of inadvertently damaging the fine nasal nerves. This damage can interrupt the sensory input that joins the trigeminal nerve, leading to a decreased or complete inability to sneeze.
Techniques for Triggering a Sneeze
When a sneeze feels “stuck” mid-process, several techniques can be used to provide the final necessary boost to the trigeminal nerve. The photic sneeze reflex, or ACHOO syndrome, is a genetically inherited trait. For these individuals, looking directly at a bright light source, such as the sun or a lamp, can stimulate the trigeminal nerve and complete the sneeze. This is believed to happen due to a cross-wiring of the visual and sneeze pathways in the brain.
Mechanical stimulation of the nasal area is another effective method to provide the final sensory input. Gently tickling the inside of the nose with a clean tissue can directly stimulate branches of the trigeminal nerve. This action mimics the original irritant, pushing the signal past the necessary threshold for the reflex to fire.
A change in temperature or the introduction of a strong scent can also help to complete the reflex. Stepping into a colder environment from a warm one can stimulate the nasal nerves. Similarly, inhaling a small amount of a strong scent, like a spice, can provide the final chemical irritation needed to trigger the protective expulsion.