Have you ever stepped outside on a cold winter morning and suddenly let out a loud sneeze?
On the other hand, when you enter a dusty room or when you have a cold, you may find yourself coughing uncontrollably.
Both are reactions that the body tries to expel foreign substances, but why does it sometimes come out through the nose and sometimes through the mouth?
Sneezing and coughing are both defense mechanisms for protecting the respiratory tract.
However, their mechanisms and roles are surprisingly different.
Although we produce these reactions unconsciously, there are actually sophisticated mechanisms at work in our bodies.
Knowing the difference between coughing and sneezing may give you insight into how your body fights off external invaders.
Let’s start by looking at how sneezing works.
“Instantaneous defensive reaction” and “sustained defensive reaction”
Although sneezing and coughing may seem similar, they have very different functions.
What’s similar is that both attempt to push out foreign objects that have entered the body by using the force of air released from the lungs .
But beyond that, sneezing and coughing have very different purposes.
Sneezing is a spontaneous defense mechanism that is triggered when a foreign object gets into your nose .
Pollen, dust, smoke, and even sudden changes in temperature can all make you sneeze.
The nasal mucosa contains sensors called “mechanoreceptors,” and when these detect a foreign object, they send a signal via the trigeminal nerve to the “sneezing center” in the medulla oblongata of the brain.
Upon receiving this signal, the brain draws a large amount of air into the lungs in one go, closes the glottis to increase pressure, and then releases it explosively in an instant.
Air is then expelled from the nose at speeds of over 100 miles per hour , expelling any foreign objects.
It is said that when you sneeze, approximately 40,000 droplets are produced .
These droplets contain relatively large particles, so although they do not remain in the air for long, they have the tendency to spread rapidly and over a wide area.
On the other hand, coughing is a defense mechanism to expel foreign objects that have entered the trachea and lungs .
It can occur when you have a cold, when food particles get stuck in your throat, or even when you inhale smoke or cold air.
Like sneezing, coughing is controlled by signals sent through the vagus nerve to the cough center in the brain.
When sensors in the airway detect a foreign object, a command is sent to the brain to “expel it!”, causing the diaphragm and intercostal muscles to contract and the glottis to close, causing the pressure of the air trapped in the lungs to suddenly rise.
When the glottis opens, air is expelled at speeds of over 100 kilometers per hour .
This powerful airflow pushes out mucus and foreign objects that have accumulated in the airways.
It is estimated that approximately 3,000 droplets are produced when a person coughs .
Although the number of droplets produced by a sneeze is smaller than that produced by a sneeze, a cough tends to expel very small particles.
Therefore, droplets produced by coughing tend to remain suspended in the air for long periods of time, which may increase the risk of infection, especially in enclosed spaces.
From what we’ve heard so far, coughing and sneezing seem to be almost the same reaction.
However, while we can consciously cough by clearing our throats, we cannot consciously sneeze even if we try. What is the reason for this?
Why it’s easy to hold a cough but hard to hold a sneeze
The main difference between sneezing and coughing is how easily you can control it .
For example, if you try to refrain from coughing in public, you can suppress it to some extent.
However, since sneezing is almost entirely a reflex, it can be quite difficult to consciously stop it .
When a foreign object irritates the nasal mucosa, the brain reacts instantly, causing a sneeze.
On the other hand, coughing is a mechanism for pushing out foreign objects that have entered the airways or lungs , and is basically a reflex action; however, because the cerebral cortex is also involved, it can be consciously controlled to some extent .
This is the same principle that enables us to consciously control breathing and blinking, which are normally done unconsciously.
So why do sneezing and coughing work via different mechanisms and elicit different responses?
Sneezing and coughing are reflex actions that occur when a foreign object is inhaled.
However, unlike a sneeze, a cough not only has a momentary role but also a sustained role in keeping the airways clear .
Because the airway is an important area involved in breathing, it is necessary to ensure airflow at all times, even in cases other than when foreign objects enter the airway, such as when the trachea narrows or phlegm becomes trapped.
This task cannot be performed by a simple reflex: coughing requires conscious control.
Stimuli in the airway are transmitted via the vagus nerve to the cough center, in which the cerebral cortex is also involved.
So coughing, unlike sneezing, is a flexible system that can adjust strength and frequency as needed.
Coughing has evolved as a means of communication
Because coughing can be controlled at will, it eventually evolved into a means of communication in human society .
Coughing to cover up situations that are difficult to express with words, such as clearing your throat when you feel awkward or using coughing as a way to subtly make your presence known, is a usage that arose naturally from the aspect that coughing can be used both as a reflex and to control it.
Coughing has also come to reflect a person’s psychological state .
Many people clear their throat before giving a presentation, but when we are stressed, the sympathetic nervous system becomes activated. When the sympathetic nervous system becomes dominant due to tension, breathing becomes shallow and the airways become narrow, making us more likely to cough.
If you see someone repeatedly clearing their throat while giving a speech, you can tell they are nervous, and in human society coughing has come to serve as a psychological sign as well.
Coughing has a similar function to sneezing, but because it can be controlled consciously, it has come to play a different role in human society.
When you think about it, the way the human body functions is fascinating.