by Jenny Zheng
figures by Rebecca Clements

With winter soon coming to an end (hopefully), many of us have been plagued by seemingly endless hacking that’s accompanied by phlegm, a type of mucus produced by the respiratory tract. The body starts feeling better after a week of sickness, but even after that “hell-week,” one final foe has to be dealt with: the phlegm. It’s such a nuisance that we probably just wished that all of our mucus would go away, but this overlooks the fact that the creation and coughing up of phlegm is a way for our lungs to get rid of infectious microbes. If we manage to think beyond that disgusting phlegm lodged in our throats, we can start to appreciate that our bodies constantly produce mucus to help keep us healthy. In particular, mucus can assist our immune systems by acting as a natural filter for the bacteria we interact with constantly.

So, what is mucus?

Mucus is a protective substance that’s excreted from multiple areas of the body, such as the mouth, sinuses, throat, lungs, stomach, and intestines (Figure 1). Mucus itself consists of multiple constituents, but its major component is a substance called mucin. The mucins in mucus can work as a selective barrier, lubricant, or viscous material depending on their structure. When mucin structure and production is normal, mucus protects surfaces all over our body, which helps us live alongside many different microbes. However, disease can ensue when mucin structure and production are abnormal.

Figure 1: Protective mucus is found all over the body. The zoomed-in image on the right is a cartoon depiction of the surfaces of those body parts. The pink blobs are epithelial cells, which are the outer layer of cells in many parts of the body. Mucus (the yellow cloud above the pink blobs) covers the cell’s surface and contains mucins (brown lines) that define its properties.

How can mucus prevent disease?

Professor Katharina Ribbeck’s research group at MIT wants to understand the benefits of mucus, and it has uncovered interesting properties of mucins as a result. Ribbeck’s group has purified natural mucus from a pig stomach to obtain a mucin known as MUC5AC. This pig-derived mucin is related to the MUC5AC found in multiple parts of the human body, such as the respiratory tract, stomach, gallbladder, and female reproductive organs. Since pigs and humans are closely related, the function of their respective MUC5ACs should be similar. Using liquids containing MUC5AC, they investigated the interaction between mucin and microbes in our lungs and guts, and whether the mucins might be preventing some of these microbes from causing disease.

One such microbe is a bacterium called Pseudomonas aeruginosa, which lives in our lungs and is often harmless when found in healthy individuals. However, it can cause lung infections in patients with a disease called cystic fibrosis, which is characterized by abnormal mucus production. These infections are exacerbated when P. aeruginosa starts forming sticky groups of bacteria known as biofilms on the surfaces of the lungs. Biofilm formation is often associated with increased virulence (i.e. the ability of a microbe to cause disease), and groups of bacteria in biofilms are more resistant to antibiotics. Therefore, biofilms cause infections to be more aggressive and more difficult to treat. Can we find a way to prevent biofilm formation in order to help these patients?

Voila! Ribbeck’s group found that MUC5AC can possibly prevent lung infections by making surface attachment more challenging, which can prevent P. aeruginosa biofilm formation. Conventional wisdom would lead us to believe that mucus suppresses biofilm formation by trapping bacteria, rendering them immobile, and preventing aggregation. On the contrary, Ribbeck’s group determined that the true mechanism may be opposite of this intuitive thought. In the more viscous MUC5AC solution, they saw that bacteria actually move faster. This increased motility (ability to move) decreases biofilm formation because moving cells are less likely to stick together (Figure 2), which renders the bacteria less dangerous. We are lucky to have mucus protecting us from potentially nasty bacteria.

Figure 2: Mucus disrupts biofilm formation. In healthy individuals (the left box), the bacterium, P. aeruginosa (blue cylindrical objects with tails) can move around because the mucin itself binds to the bacterium, acting as a signal for the bacterium to increase motility through the use of flagella (the tails in the picture). In the diseased state (right box), with either no mucus or abnormal mucus, the cells can stick together and form biofilms.

Another microbe made less dangerous by mucus is a yeast called Candida albicans, which can live in places like the gut, mouth, and vagina. C. albicans can cause an infection called candidiasis (a.k.a. thrush or yeast infection when in the mouth or vagina, respectively), but it is found in the gut or mouth of 80% of adults without causing any harm. However, if a healthy person contracts another sickness that weakens the immune system or changes mucus production, C. albicans can either aggregate in biofilms or form hyphae, which allow the yeast to invade human cells (damaging the cells and providing the yeast access to the bloodstream). When C. albicans is allowed to overgrow in these forms, the result can be fatal. C. albicans’ virulence is tied to its ability to invade cells through hyphae and biofilm formation, so Ribbeck’s group tested the effect of multiple mucins (including MUC5AC) on C. albicans behavior. Much like for P. aeruginosa, they determined that mucin exposure decreases virulence by mitigating biofilm formation. They also observed that it prevents hyphae formation, which further diminishes virulence.

Diagnostic potential

We have seen that mucus is highly beneficial to our health when its structure and production are normal. However, there are times when people get sick and mucin production becomes abnormal. A sick person may be producing atypical mucus, which may manifest as changes in either the amount or structure of its constituent mucins. When mucin’s structure changes, its ability to dampen the virulence of pathogens can be weakened, or the strength (characterized by viscosity and fibrosity) of the mucus itself can change. In these cases, even though mucin may not be protecting us as effectively, it may be used as an indicator of an illness or increased susceptibility to disease. One example of using mucus as a diagnostic tool is the analysis (also done by Ribbeck’s group) of the structural properties of cervical mucus to assess the risk of pre-term birth. If cervical mucus is structurally weaker (thinner and more stretchy) and more permeable—which would allow more bacteria to travel through the mucus—then pregnant women have a higher risk of pre-term birth; stronger mucus, on the other hand, indicates a lower risk of pre-term birth. Just by observing mucus, doctors can more accurately predict which pregnant women should be watched for pre-term birth.

The future

This article about mucus is just the tip of the iceberg; both the lessons we can learn from mucus and its potential uses seem unlimited. Maybe one day we will be able to explore the uncharted territory of healthy donors providing mucus to help prevent P. aeruginosa biofilm formation in cystic fibrosis patients who produce abnormal mucus. This could potentially go a long way in making antibiotic treatments more effective and reducing the chance of infection in the first place.

The more I learn about mucus, the more I realize how important it is. So, the next time we cough up some phlegm, maybe remember how mucus helps us out and appreciate what comes up.

Jenny Zheng is a second-year Ph.D. student in the Department of Molecular and Cellular Biology at Harvard University.

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36 thoughts on “All About That Mucus: How it keeps us healthy

  1. Very interesting. My mucus problem is unusual in that I have MDS with heavy clear mucus draining into my lungs and stomach from my sinus. I am immune deficient but never get colds or infections. I believe my body is making profuse amounts of mucus to help my body filter any infections and therefore I should not try and stop the mucus.

    1. Get more iodine. 300 mcg. a day. Buy sea kelp capsules. Low dose. Like 150mcg of iodine per pill.

  2. My problem for the last couple days has been that my body seems to have stopped making those protective layers, so I can’t keep my mouth moist, my sinuses are rubbed raw and my stomach is all out of whack, it’s truly painful. I can’t seem to drink enough water or get enough moisture in the air to feel comfortable. What do you do to encourage healthy mucus production? I need my natural lubricant back! 😭

    1. As a nutritionist .. I am frequently telling people with too much mucus to lay off certain very common foods. Namely the bread, biscuits, pies and pizza that make up too much of what many consume. So you should do the opposite! Enjoy pasta (wheat) pizza etc. Enjoy a croissant or two, or pancakes etc. If you have wheat or gluten issues this will need more consideration. Oats are also pro mucus. I’m sure being bad for two days is good.

      1. Brilliant! That’s just the information I was looking for. Will this increase mucous in the nose and stomach too because I think I need this . 🤗

      2. Malcolm, thanks for the suggestion. Oats have been helping a bit. I am gluten sensitive. Do you have any other suggestions?
        How about consuming aloe?

  3. What do you all think about eating natto which has nattokinase?, which is a fibrinkinase which breaks down fibrin and biofilm.

  4. I have inflammation in the airways and keep coming every year for the past five years now.
    As described as I have lung fibrosis , I keep coughing for at least 6 to 8 weeks each time I get it. The only solution is to take heavy doses of cortisone and antibiotics for long time and still coming back every year. Any suggestions on what to use naturally to help me with this problems. Thank you in advance for all your help.

    1. Make sure all nutrition needs are met. You could be deficient in B-vitimins, Amino Acids, lipids or minerals. Any other clues (complaints). Get a nutrition or mineral analysis somewhere.

    2. Freshly chopped
      Avoiding dry cold air humidifier
      Rubbing eucalyptus oil on chest

    1. Try simple Jalaneti,
      Physical cleaning of your sinus cavities with Luke warm water with little sea salt through each nostril alternatively.

      This will reduce congestion immediately, clear throat and help reduce any kind of allergies anywhere in your body in the long term.

      For Dry Cough, use above saline water and Gargil and cough out the phlegm.

  5. Kudos to this article and please note/respond to the comment on enzymatic release of biofilm, if you can.

    As our disease defenses evolved, those allowing survival remained in our gene pool pretty much just as they are. They did the job .. despite their non lethal shortcomings. Metabolic energy is incredibly challenged already and does not branch into ‘lablike’ moments of “Hey! Lets make it go faster and better” …unless that translates into outrunning the tigers, right?

    We are so lucky to be graced with an intelligence that can steward and manage our own life processes
    (and other lives and species, for that matter!)
    But we are so doomed if we don’t appreciate our gift of greatness with high honor and deep sense of responsibility.

    Selectively focusing on symptoms of complaint without supporting our long evolved pathways of cure has detoured clinicians and pharmacologists into gurus of wealth not health. Somewhere… (a major medical convention, they say)… the Hippocratic Oath took a hypocritical turn from the famous words,
    “First… Do no harm”
    .. to an inglorious,
    “First… Do business!”

    But that’s probably our fault. Man chronically misinterprets. We quickly pay for the first person who will “just get rid of my pain (or snot) so I can breathe easy and get back to work …I just don’t want to be bothered with it anymore!”
    … erm. Be careful what you wish for!!!

    Thanks for a proper look at this busy monster within us.. All it ever wanted was a little help and understanding.
    The Nosebleed Poem … by Henry Gibson.
    “I THINK my nose is bleeding!!!
    BUT itsnot”

  6. I’m very scared because my body isnt producing any mucus at all. My nose is bone dry. All my organs are starting to shut down
    It started with supposed sinus infections but turns out my sinuses were dry. So can may cavities in mouth and a distal cracked tooth be the cause of no mucus production ?

    1. Hi Tammy

      I had a life threatening seziure last Friday and then something was eating my body I could feel I was dying. No one could fine anything through blood, ecg and x ray. No mucus, cough or sneezes. Now Im well but nooo mucus whatsoever and high blood sugar that spikes instantly as I eat.

      Cant find any info and a bit worried if I had autoimmune disease. You posted in 2020 almost a year ago now, did you find out anything? Did you get your vaccine before these issues? I had mine at start of June

      1. Try drinking about 8oz of pomegranate or cransberry juice (best to make the juice yourself) daily for about 3-4 weeks. Dr. William Li has talked about helping his patients build gut membrane’s mucus using that method, I don’t know if it’ll work for all types of cells or just the gut. But just check out Dr. William Li’s video on Youtube if you’re interested in more healing food.

    2. Dry eye and dry mouth?? Could you have an autoimmune disease known as Sjogrens Just a thought. I have Sjogrens. It’s only a thought.

  7. This article is filled with partial truths and selective thinking
    The vast majority of people need mucus only because they eat foods that cause inflammation and the body is constantly trying to fight it

    Those who describe being very dry simply have gone so acidic that the body is in severe cellular dehydration
    Drinking water won’t do anything for you
    What you must do is alkaline your body by removing the acids

    Since LIVINGMucusFREE I have resolved all my health issues and never get a cold or bug anymore. This does not mean I have zero mucus but rather that I don’t have excess mucus for bacteria to breed and propagate AND my body is predominantly alkaline ~as it should

    Mucus and biofilm is something we want to minimize and get rid of as it is breeding ground for pathogens
    Eating a diet high in fruit and high water content veggies, ideally raw, is THE best way to ensure health

  8. Hi,
    Great article. This sounds like very interesting research.
    I have an issue with too much mucous production in my mouth and nose, which is frustrating as I’m a singer. Could the fact that we have an air conditioning system in the house be drying out my body too much and therefore my body creating too much mucous to protect me from bacteria. With this thinking, is it worth getting a humidifier to reintroduce healthy moisture back into the home environment in an attempt to holt my body into producing the extra bacteria. I’ve tried everything else, as has my doctor.
    Thank you for your research. I know how time consuming it is.

    1. Try simple Jalaneti,
      Physical cleaning of your sinus cavities with Luke warm water with little sea salt through each nostril alternatively.

      This will reduce congestion immediately, clear throat and help reduce any kind of allergies anywhere in your body in the long term.

      For Asthama, repeat Jalaneti every alternative day for few weeks and you will find amazing results.

      Do your basic cleaning activity and allow body to cure on its own.

      Try it.

  9. I’m positive I’m a hypochondriac, but I also have real ailments I’m coughing up phlegm that’s clear with grey spots and/ or at times with little squiggly black fibers. Also I had a tick bite over 10 yrs ago that left a bulls eye I’ve been tested for all sorts of stuff but test came back negative for everything except oral herpes and that makes me feel disgusting inside like I am unable to clean the filth off. I heard that the fibers could be spirochets, and my heart is beating irregular, I can’t get proper health care because I’m not apart of the upper class. I don’t want narcotics I just want cured of my ailments. I can get high off morning glorys or licking a toads ass. I need help and I will take good advice but don’t tell me I need a shrink I actually need to enlarge I’m small enough. I’ve even asked Jesus but it seems he may be to busy at the moment and it’s not pressing enough, if you can help please doo oh my next stop is a voodoo witch doctor. Thanks 😊 and hopefully I get well soon.

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