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Mucus in the Human Body: Functions and Health Problems

Updated on January 24, 2017
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Linda Crampton is a teacher with a first class honors degree in biology. She writes about human biology and the scientific basis of disease.

A human's eyes, nose and mouth contain protective mucus.
A human's eyes, nose and mouth contain protective mucus. | Source

Mucus in the Body

Mucus has a reputation as a gross substance and is one that many people would like to avoid. It's actually a very useful material with important functions. It destroys bacteria and viruses, traps particles such as dirt, prevents water loss, humidifies passageways, lubricates the movement of materials, and protects surfaces from damage.

Mucus is a slippery liquid made by mucous membranes, or mucosas. The membranes line the passageways in our bodies that connect to the outside environment. These passageways include the nose, the mouth, the airways, the digestive tract and the reproductive tract. There is also a mucous membrane over the white part of the eye and on the inside of the eyelid.

Mucosas consist of thin surface layers on top of a supporting layer of connective tissue. Many contain glands that produce mucus, but some-including those in the urinary tract-—make no mucus or only a tiny amount.

We produce extra mucus when we have a cold or the flu.
We produce extra mucus when we have a cold or the flu. | Source

Composition and State of Mucus

Mucus contains water, proteins such as mucins, antibodies, antiseptics, and salts. Mucins are glycoproteins, which are proteins with attached carbohydrates. The carbohydrate coating gives mucin molecules a large ability to absorb water. Antibodies help the immune system to attack pathogens (organisms that cause disease), while antiseptics kill pathogens directly.

Although mucus is important in many places in the body, for most of us its presence is most obvious in the nose and the respiratory tract. People may not deliberately look at their nasal mucus, or snot, but they may accidently notice that it occasionally has an unusual appearance. The change is usually temporary and harmless, but sometimes it indicates a problem, as described below.

Mucus function in the respiratory system
Mucus function in the respiratory system | Source

We produce between one and two liters of mucus in our respiratory tract each day. If we have a respiratory infection we produce even more.

The Role of Cilia in the Respiratory Tract

In the airways of the lungs, mucus traps inhaled particles and humidifies the air. Tiny hair-like structures called cilia line the airways. The cilia beat in a coordinated pattern, sweeping the mucus up to the back of the throat, where it's swallowed or released into the nose.

Smoking can damage the cilia, resulting in a buildup of mucus in the respiratory tract. The collection of mucus can make breathing difficult and cause a person to cough frequently in an effort to remove the blockage.

The Paranasal Sinuses

1 - frontal sinus, 2- ethmoid sinuses or ethmoidal air cells, 3 - sphenoid sinuses and 4 - maxillary sinuses
1 - frontal sinus, 2- ethmoid sinuses or ethmoidal air cells, 3 - sphenoid sinuses and 4 - maxillary sinuses | Source

The Sinuses

The paranasal sinuses are hollow spaces in the facial bones. They are lined with a mucous membrane that produces mucus. The function of the sinuses is unknown, but there are several theories about their job. They may humidify the air that we breathe, protect sensitive areas such as the roots of the teeth from rapid temperature changes, lighten the skull, acts as crumple zones during an impact, or increase the resonance of our voice.

Sinuses aren't isolated but are connected to other structures in the face, including the nose. This means that bacteria can travel into a sinus and cause an infection. A sinus infection is called sinusitis. It involves inflammation of the sinus lining and excessive mucus production. The mucus may be yellow or green in color and is discharged through the nose or into the throat through post-nasal drip.

Colored Nasal Mucus or Snot

Mucus freshly produced by the respiratory system is colorless. When it's removed from the nose, it may be grey, white, yellow, green, brown, black, orange, pink, red, or a rust color. Colored snot sometimes indicates a health problem, but this isn't always the case.

Some common reasons for changes in mucus color are listed below. There are other reasons for some of the changes, though. A doctor should be consulted if someone is concerned about the appearance of their nasal mucus.

The nose of humans and other mammals contains snot.
The nose of humans and other mammals contains snot. | Source

Grey, White, Yellow, or Green Snot

Grey

Trapped mucus that is removed from the nose is often grey in color due to the dust and dirt that it contains and the fact that it has partially dried out. The dried clump of mucus is colloquially known as a "booger".

Cloudy or White

A cloudy appearance suggests that tissues are inflamed and swollen, causing mucus to move more slowly, lose moisture, thicken and become cloudy. The inflammation may be due to an infection or an allergy. Mucus that is white rather than cloudy may indicate an infection such as a cold.

Yellow or Green

Yellow or green mucus doesn't necessarily indicate that an infection is present. If the colors are persistent, however, a viral or bacterial infection may exist. The Cleveland Clinic recommends that people see a doctor after twelve days with green mucus. Harvard Health Publications recommends a doctor's visit after ten days. If other symptoms are present in addition to the colored mucus, however, a doctor should be visited much sooner.

The green color is due to the presence of a colored enzyme called verdoperoxidase, which is released by white blood cells, or leukocytes. Some of these cells actively fight pathogens. Others are involved in the inflammatory response.

Medical sources sometimes differ in their ideas about the significance of mucus color. They all agree on the following points, however. If an unusual color persists, or if the change is accompanied by other symptoms such as a fever, a doctor should be consulted.

Brown, Black, Orange, or Red Snot

Brown or Black

Brown mucus can be caused by dirt in the nose or by the presence of blood. Black mucus may be produced by a major fungal infection that requires medical treatment. Tars obtained from cigarette smoke can stain mucus in the respiratory system brown or black. Coal miners may develop black mucus as well due to the inhalation of coal dust.

Orange, Red or Rust-Colored

People with pneumonia may produce mucus with a burnt orange color, which is produced by the presence of blood. Anyone with pneumonia should be under a doctor's care. Pink, red or rust-colored mucus also indicates the presence of blood. In these cases the blood may be produced by a minor wound in the nostrils. If the red color persists or if a large amount of blood is released, however, a doctor's advice should be sought.

The digestive tract is lined with a mucous membrane that produces mucus.
The digestive tract is lined with a mucous membrane that produces mucus. | Source

Mucus in the Mouth and Stomach

Mouth

Saliva in the mouth contains mucus with a thin consistency. This mucus is an excellent lubricant and makes swallowing food easier.

Stomach

The stomach lining is covered by a protective layer of mucus. Glands in the stomach produce mucus, hydrochloric acid and an inactive enzyme called pepsinogen. In the stomach cavity, the hydrochloric acid changes the pepsinogen into an active digestive enzyme called pepsin. This enzyme digests proteins. The mucus layer acts as a barrier which prevents the stomach lining from being attacked by pepsin and acid.

If the mucus layer in the stomach is thinned or removed, which may happen during an infection by a bacterium called Helicobacter pylori, pepsin and acid may be able to attack the stomach lining. The infection can cause inflammation (gastritis) and sores called ulcers.

This is part of the mucosa lining the small intestine. The folds are known as villi. They increase the surface area for the absorption of digested food.
This is part of the mucosa lining the small intestine. The folds are known as villi. They increase the surface area for the absorption of digested food. | Source

The Intestine

Glands in the lining of the small intestine and the large intestine also produce mucus. There is often some mucus in stool, but generally not enough to be noticed. Noticeable amounts may appear in intestinal problems such as the diarrhea-predominant form of irritable bowel syndrome (IBS). The mucus looks like a thin, glistening jelly. In ulcerative colitis, the lining of the large intestine is inflamed and ulcers develop. Mucus and blood are often released into the stool in this disorder.

The Reproductive Tract

The cervix is the lower end of the uterus. Glands in this area produce cervical mucus. The consistency of this mucus changes during a woman’s monthly cycle as the reproductive hormone levels change in her body. Cervical mucus helps to prevent infection and supports or inhibits sperm movement.

After menstruation, very little cervical mucus is made. As the cycle progresses, the amount increases. The mucus is white or cream in color and is sticky. Around the time of ovulation, when an egg is released from an ovary and a woman is most fertile, the mucus is most abundant and is colorless, thin and often stretchy. This is the best texture to allow for sperm penetration. After ovulation, the mucus decreases in amount, becomes cloudy and develops a sticky texture again.

Mucus is important in the eye.
Mucus is important in the eye. | Source

The Eyes

The conjunctiva is a mucous membrane that covers the white part of the eye (the sclera) and the inside of the eyelid. It produces a thin mucus that lubricates the eye and contributes to tear formation. Tears have three layers—an inner mucus layer made by the conjunctiva, a watery middle layer made by the lacrimal gland and an oily outer layer made by the meibomian glands in the eyelids.

Once tears and mucus have spread over the surface of the eye, they drain into the nose through small openings at the inner corner of the eye. Each opening is called a lacrimal puncta, or a puncta lacrimalia. Some people wake up in the morning with dried particles of mucus in the corner of their eyes due to inadequate drainage while they are asleep and not blinking.

Surface structure of the eye
Surface structure of the eye | Source

An abnormally large amount of mucus is made in some health disorders. Cystic fibrosis results from a mutation in both copies of the gene for a protein called cystic fibrosis transmembrane conductance regulator, or CFTR. A major symptom is excessive production of a thick mucus.

Health problems associated with cystic fibrosis
Health problems associated with cystic fibrosis | Source

Cystic Fibrosis or CF

Cystic fibrosis is a genetic disorder in which the body makes mucus that is much thicker and stickier than normal. The thick material can't move very easily and collects in body passages. Mucus in the breathing tubes makes it difficult to breathe and frequently leads to bacterial infections. In addition, mucus often blocks the tube that transports digestive enzymes out of the pancreas to the small intestine, resulting in reduced digestion of foods— especially carbohydrates and fats—and therefore reduced nutrient absorption.

People with cystic fibrosis generally have a shortened life. However, the good news is that the average lifespan for patients is increasing rapidly in many countries due to improved treatments. The goal of research is to give patients a normal lifespan and a better quality of life.

As the teenager in the video below describes, a significant part of each day in a CF patient's life is spent on treatments to clear the lungs. Hospitalizations are sometimes necessary to accomplish this process. In addition, digestive enzymes must be taken with all meals and snacks in order to obtain enough nutrients from food.

Living With Cystic Fibrosis

Asthma

Asthma is another problem that involves the production of more mucus than normal. People with the disorder have airways which are sensitive to specific allergens or irritants. The irritants include dust mites, cold air, cigarette smoke, certain food components, or exercise. During an asthma attack, the airways become inflamed and swollen, restricting the passage of air. The airways produce extra mucus, which further blocks the passage of air. In addition, the muscles that surround the airways contract, constricting the air passages. A wheezing or whistling sound is often heard as the person breathes.

Asthma can be treated and managed, but it can't be cured. Many asthmatics find that with their doctor's guidance they can reduce, weaken and even eliminate asthma attacks. Sometimes asthma is harder to manage, however, and may occasionally be a medical emergency.

What Happens During an Asthma Attack?

Bronchitis

Bronchitis involves inflammation of the airways and excessive mucus production. Acute bronchitis lasts for only a short time and is generally caused by a viral infection. Chronic bronchitis lasts for a long time and is often permanent. It usually results from smoking or from chronic inhalation of certain chemicals or pollutants.

People suffering from acute bronchitis may produce colored mucus in their airways. This mucus may be white at first and then change to yellow or green. The color may indicate the presence of white blood cells associated with inflammation rather than a bacterial infection. As always, if symptoms persist or get worse, a visit to a doctor is in order.

Mucus coughed up from the respiratory system is sometimes called phlegm. Sputum is phlegm mixed with saliva.

COPD results in excessive mucus buildup and serious lung damage.
COPD results in excessive mucus buildup and serious lung damage. | Source

Chronic Obstructive Pulmonary Disease or COPD

Chronic bronchitis and emphysema are the two most common diseases classified as a Chronic Obstructive Pulmonary Disease. Both are caused chiefly by smoking but may be worsened by inhaling polluted air. Symptoms include wheezing, shortness of breath, and coughing up mucus. Unfortunately, the trigger that causes the disease damages the lungs and the disorder is progressive. The sooner the condition is diagnosed and the trigger avoided, the better the outcome.

People with COPD can have either chronic bronchitis or emphysema, but they often have both conditions. The alveoli are tiny air sacs in the lungs in which oxygen is absorbed into the blood. In emphysema, the walls of alveoli break down, making exhalation difficult.

Mucus: Friend and Foe

Mucus is an essential substance in the human body and is usually a friend, despite its unpleasant reputation. However, at times, or in certain people, too much mucus is made and the mucus is transformed from a useful material into a dangerous foe. This is especially sad in diseases that affect the quality of life. Hopefully medical research will continue to discover improved ways of dealing with excess mucus and its consequences.

© 2011 Linda Crampton

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    • AliciaC profile image
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      Linda Crampton 4 weeks ago from British Columbia, Canada

      Thank you, Simran. I appreciate your comment.

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      Simran 4 weeks ago

      Thanks for great information

    • AliciaC profile image
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      Linda Crampton 5 weeks ago from British Columbia, Canada

      Hi, Teshome. A soft spot or fontanel on a baby's head does sometimes pulse as the heart beats. The soft area is a place where the skull bones haven't yet fused. The sinuses or air spaces are located further away in the forehead and face.

    • AliciaC profile image
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      Linda Crampton 2 months ago from British Columbia, Canada

      No, not as far as I know. Epilepsy arises due to an electrical disturbance in the brain.

    • profile image

      Faustina 2 months ago

      Can Epilepsy caused by Mucus

    • AliciaC profile image
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      Linda Crampton 3 months ago from British Columbia, Canada

      Thank you. I appreciate your comment.

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      Malar Vizhi Siddharthan 3 months ago

      Good article with in-depth information. Thanks for sharing

    • AliciaC profile image
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      Linda Crampton 5 months ago from British Columbia, Canada

      Thank you very much, Mary. I appreciate your visit.

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      Mary Norton 5 months ago

      Your article clearly explains to me many things I just took for granted before. I wish these things were taught to us in school.

    • AliciaC profile image
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      Linda Crampton 3 years ago from British Columbia, Canada

      Thanks for the comment and for sharing the information, Biocurious World.

    • profile image

      Biocurious World 3 years ago

      Well expressed and nicely explained..good one..at the time of pregnancy also mucous secreation increases.

    • AliciaC profile image
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      Linda Crampton 5 years ago from British Columbia, Canada

      Thank you for the comment and the vote, Brinafr3sh!

    • Brinafr3sh profile image

      Brinafr3sh 5 years ago from West Coast, United States

      Hi Alicia, Interesting hub, thanks. Voted up.

    • AliciaC profile image
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      Linda Crampton 5 years ago from British Columbia, Canada

      Thank you for the comment, Lucy.

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      Lucy 5 years ago

      I like your story. Very nice

    • AliciaC profile image
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      Linda Crampton 5 years ago from British Columbia, Canada

      Hi, Perspycacious. Thanks for the note, which I've edited. I check my hubs many times after I write them, but this word slipped by me! I'm glad that you found help for your sinusitis.

    • Perspycacious profile image

      Demas W Jasper 5 years ago from Today's America and The World Beyond

      Well proofread for such a long, informative article. One I noticed was: "red or rust colored mucus indicates the present of blood." Some present!;o) I used to have lots of sinusitis until I had a sinusectomy as part of fixing a deviated septum from a broken nose achieved from playing football. Since then, few problems. Wonderful blessing.

    • AliciaC profile image
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      Linda Crampton 6 years ago from British Columbia, Canada

      Thank you very much, James.

    • James A Watkins profile image

      James A Watkins 6 years ago from Chicago

      I found your article on mucus to be quite enlightening. Thank you for the education. It is very good.

    • AliciaC profile image
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      Linda Crampton 6 years ago from British Columbia, Canada

      Thank you, michael hooper.

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      michael hooper 6 years ago

      thanks for info learnt a lot

    • AliciaC profile image
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      Linda Crampton 6 years ago from British Columbia, Canada

      Thank you, GetSmart! It's nice to meet you too.

    • GetSmart profile image

      GetSmart 6 years ago

      This is a very informative hub. I am very glad I found you here and look forward to reading more!

    • AliciaC profile image
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      Linda Crampton 6 years ago from British Columbia, Canada

      Hi, toknowinfo. Thank you very much for the comment and the rating.

      Hi, mistyhorizon2003. I suffer from asthma so I‘m familiar with mucus as well! Thanks for your comment.

    • mistyhorizon2003 profile image

      Cindy Lawson 6 years ago from Guernsey (Channel Islands)

      Excellent hub and on a topic that is important, (spent a large chunk of my childhood suffering from chest infections, colds and asthma so know a lot about being 'full of Mucus'). Well written. Thanks

    • toknowinfo profile image

      toknowinfo 6 years ago

      Great hub. My whole family and I have the flu so mucus is on my mind. Thanks for an informative article. Rated up and useful.

    • AliciaC profile image
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      Linda Crampton 6 years ago from British Columbia, Canada

      Thank you for the comment, CMHypno.

    • CMHypno profile image

      CMHypno 6 years ago from Other Side of the Sun

      Never really given much thought to mucus before, so thanks for all of the great information AliciaC.

    • AliciaC profile image
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      Linda Crampton 6 years ago from British Columbia, Canada

      Hi, Prasetio. Thank you for your kind comment and vote. Best wishes to you.

    • prasetio30 profile image

      prasetio30 6 years ago from malang-indonesia

      Good information. Very well written and useful for us. I always care with healthy life and you gave valuable information about "Mucus in the body". Thanks for writing this. Vote up. Take care!

      Blessing and hugs, Prasetio

    • AliciaC profile image
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      Linda Crampton 6 years ago from British Columbia, Canada

      Thank you for your comment, tnvrstar!

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      tnvrstar 6 years ago from doha, qatar

      great article thanx for sharing it :) your article remembered my past classes of biology where i have to learn a lot of things about mucus membrane