The sneezing is an innate reflex which consists of the very rapid expulsion of air from the lungs through the nose and mouth. It is a defense reflex that clears the airways from foreign bodies such as dust and allergens. When we hold it, however, the air that would normally be expelled from the nose can accumulate causing damage. In these cases, in fact, the pressure of the air we hold increases significantly in the lungs, chest and head, and, if it is not releasedcan also damage blood vessels, leading to hemorrhages or even brain damage. Additionally, the pressure can damage the rib cage, causing fractures or lung injuries. Although these injuries are rare, the risk exists, especially in people who may have pre-existing conditions. So rather than holding back it is always better to sneeze.
What is sneezing and what is it due to
Sneezing serves a function similar to that of a coughor the liberation of the airways, through the expulsion of an intense flow of air: it is in fact a defense mechanism of the body. In the nose there are nerve endings capable of signaling the presence of foreign bodiessuch as dust, allergens and more. When these elements are present, the trigeminal nerve sends a signal to specific centers in the brain, which relay it to the lungs, diaphragm and other muscles. This passage of information starts a sequence of involuntary actionsautomatic, which are not under our control.
First of all, it happens an inspiration more or less deep. Immediately afterwards the glottis closesa set of muscles that separate the pharynx from the airways. Then one happens compression of the lungs with the glottis closed and the air contained in the lungs reaches a considerable pressure. In the end, the sudden opening of the glottis will allow this compressed air to escape at great speed, coming out of the mouth and nose, freeing them from any foreign bodies.
So sneezing, as annoying as it may be, actually is a defensive reaction fundamental, without which potential upper airway pathogens could end up in our lungs, exposing us to the risk of serious damage and infections. In theory, therefore, holding back a sneeze prevents this defensive function from taking place, and furthermore the consequences can be much more concrete and immediate.
What happens in the lungs when you sneeze: the physics of sneezing
To understand the concrete risks that arise from a held sneeze, we must refer to one famous physical law and return to the sequence of actions that generate the airflow. The lBoyle’s lawor isotherm law, relates the volume and pressure of a gas explaining that, at constant temperature these two parameters are inversely proportional.
In practice this means that, by keeping the temperature constant, the increase in the volume of a gas leads to a decrease in the pressure it exerts, and vice versa: compressing a gastherefore reducing its volume, the pressure increases. When we close the glottis, we isolate the air in the lungs and then compress it, reducing its volume via the intercostal, abdominal and neck muscles. By doing so, increases the air pressure in the lungswhich pushes with greater force against the glottis, the only possible outlet.
Normally, as soon as the glottis opens, the pressure vents outwards. But if we cover our nose and mouth, the pressure it redistributes internallyand can thus cause dangerous effects.
What happens if we hold back our sneezes: the consequences
Sneezing without putting up resistance is far safer than holding it in, because, even if rare, the risk of internal damage exists: in fact, several injuries caused by held sneezes, the extent of which depends on the pressure that the sneeze generates.
Lesions can be grouped into cardiovascular and non-cardiovascular. The injuries cardiovascular derive from the fact that the pressure of the sneeze, if not vented, increases the intra-thoracic pressure, making blood flow to the chest is difficult from districts such as the abdomen and head. In fact, the blood in these districts must overcome a pressure much higher than normal.
This sudden increase in venous pressure can affect the ocular capillaries, leading, in the most extreme cases, to minor hemorrhages or microfractures in the eye sockets. Sometimes effects on the brain can also be observed: blood pressure which can’t get down to the chestcan be diverted towards the nasal sinuses and small arteries of the skull, which thus risk being damaged, causing, in rare cases, intracranial hemorrhages.
In lesions non-cardiovascularat chest level, the danger comes from the fact that the pressure can push against the very structure of the lung and rib cage. In some cases, the result can be a small lung collapse or the formation of small air pockets under the skin, a phenomenon called emphysema subcutaneous. They have even been reported rib fractures.
Although these injuries have sometimes occurred in the presence of risk factors, such as previous fractures of the skull bones or in patients with lung diseases, according to a review published inAmerican Journal of Rhinology and Allergy, the majority (65%) is occurred in individuals without risk factors.
