All that glistens is snot gold (or green, or yellow) 


    By Lauren Donley 

    Cold and flu season is upon us, which means that noses across the west are running wild. But have you ever stopped to consider where all that excess mucus comes from? And then, where it goes? Well, make yourself a steaming hot lemon and honey drink, and let’s wade through the thick and thin of it all. 

    Mucus is a slimy secretion produced in the areas of your body that come into contact with the outside environment, either directly or indirectly. This includes your nose, sinuses, throat, lungs and stomach. The role of mucus is to keep these tissues lubricated, and to help prevent foreign substances from passing deeper into your body and circulation. Around 95 percent of mucus is water; the rest is mainly antibodies, salts and a protein called mucin. 

    Up until now, you’ve probably had no reason to consider the fact that phlegm, snot and boogers are all different types of mucus. Phlegm is the thick mucus made by cells lining your lungs and upper airways. Once phlegm travels up from your lungs into your nose, it’s referred to as snot (or nasal mucus). As it hardens, mucus turns into boogers (or dried nasal mucus). 

    Given its sticky consistency, mucus is very effective at trapping potentially harmful substances such as viruses, bacteria, dust and dirt. These substances are then pushed up and out of your airways by tiny hair like structures, known as cilia. As this transport of mucus occurs against the force of gravity, it’s also sometimes called the mucus escalator. Obscurely, studies have shown that the mucus escalator travels at an approximate speed of one millimetre per minute. 

    Although this might not sound like much, your nose actually produces over 100 millilitres of mucus on a typical day (and night), which is nearly half a cup. If this volume seems surprisingly high, it’s probably because you’re blissfully unaware of this slow moving mucus. Most of it simply flows straight back down your throat and into your stomach, where it’s treated like any other waste product. 

    However, this constant stream of mucus becomes much more apparent during illness. In fact, the changing colour and consistency of your mucus can provide some handy insights into the type and stage of your illness (although this is by no means an exact science, so please see your doctor for a definitive diagnosis). 

    For example, at the beginning of a cold, your mucus usually changes from thin and watery, to sticky and white. This is because the common cold virus triggers the release of histamine – a chemical that inflames the mucus membranes lining your nose and airways. Mucus flows more slowly through inflamed and swollen nasal passages, so it becomes thick and cloudy as it loses moisture. 

    As a cold progresses, your inflamed membranes produce more mucus in an attempt to engulf invading viruses and bacteria, to push them out of your nose and sinuses. An increasing number of white blood cells also flood into your nasal passages to help fight the infection, which causes the colour of your mucus to change from white to yellow or green. A few days into a cold, the colour of your mucus usually changes back to clear, and the flow returns to normal, a sign that your body is effectively clearing the infection. And you will go back to quietly swallowing that half cup of mucus from your nose without even noticing. 

    Human Interest
    Human Interest
    Welcome to your regular column on the science of human beings…and being human. Brought to you by Lauren Donley, an unashamed science nerd who never misses an opportunity to share a story about bodily functions. Please note that this article is for general interest and is not a replacement for medical care. If you have any questions or concerns about your health, please contact your doctor.

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