“ACHOO” is more than just the sound made when sneezing; it is actually the acronym for the Autosomal-dominant Compelling Helio-Opthalmic Outburst syndrome, in which one sneezes upon sudden exposure to bright light.
When people think of sneezing, the most common causes people relate it to are colds or irritations in the nose, such as pepper. This is logical, considering the function of a sneeze (also known as a sternutation) – to cleanse the nasal passages by expelling foreign particles through an expulsion of air. However, there are many unexpected causes of sneezing: exposure to bright light, excessive eating, sexual excitement, and even eyebrow plucking.
The basic sneeze reflex begins with an irritation in the nasal passages, triggering the release of histamines. These in turn excite the fifth cranial nerve: the trigeminal nerve responsible for sensation in the face. Impulses travel through the trigeminal nerve network to a set of neurons in the brainstem known as the “sneezing center.” In response to these signals, the brain activates the muscles required to open the nasal and oral cavities, releasing a powerful burst of air and bioparticles in the process. The full mechanism uses a wide range of muscles, including those of the abdomen, chest, diaphragm, neck, face, and eyelids. The combined strengths of these muscles result in sneezes so powerful that they can reach speeds of up to one hundred miles per hour.
The overstimulation of any nerve associated with the trigeminal nerve can result in the sneeze reflex. In the case of the ACHOO syndrome, also known as the photic sneeze reflex, the overstimulation of the optic nerve triggers the trigeminal nerve, resulting in a series of impulses that causes one to sneeze. Sneezing as a response to overeating is a medical disorder known as snatiation. This is thought to be a genetic condition which is passed on as an autosomal dominant trait. Eyebrow plucking, oddly enough, causes sneezes quite commonly. The plucking of hairs excites a branch of the nerve that is in close proximity with the nasal passages. Although the impulses do not come directly from the nose, the act of eyebrow plucking causes the entire nerve to become more sensitive, allowing enough impulses to reach the sneezing center to generate a sneeze.
As a semi-autonomous reflex, sneezing is not a mechanism that is thought about often. Analyzed in greater depth, however, sneezing becomes an intricate miracle – a chain of reactions within a network of nerves that cleanses the nose in a matter of seconds.