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Mucus in the Human Body: Functions and Health Problems

Linda Crampton is an experienced teacher with a first-class honors degree in biology. She writes about 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.

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 some 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. A mucous membrane is also located 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 none 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.

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 accidentally notice that it occasionally has an unusual appearance. The change is usually temporary and harmless, but sometimes it indicates a problem, as described below.


The information in this article is intended for general interest. Anyone who has a problem with the mucus made in their body should consult a doctor for a diagnosis and treatment recommendations.

Mucus activity in the respiratory system

Mucus activity in the respiratory system

The Function of Cilia in the Respiratory Tract

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. In the airways of the lungs, the 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

The Nature of the Sinuses

The paranasal sinuses are hollow spaces in the facial bones. They are lined with a mucous membrane that produces mucus. The function or functions of the sinuses are unknown. 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, act 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.

Grey, White, Yellow, or Green Mucus


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 the colored mucus production is copious or if additional symptoms are present, a doctor should be visited much sooner.

The green color is due to the presence of a colored enzyme called myeloperoxidase (once known as verdoperoxidase), which is released by white blood cells, or leukocytes. Some of these cells actively fight pathogens. Others are involved in the inflammatory response, which often accompanies allergies. Yellow or green mucus may therefore appear due to allergies or infections.

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 Mucus

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.

Mucus in the Mouth and Stomach


Saliva in the mouth contains mucus with a thin consistency. This is an excellent lubricant and makes swallowing food easier. By making the food slippery, the mucus reduces the chance that it will injure the esophagus.


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 that 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.

Intestinal Glands

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 material 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.

The Conjunctiva in the Eye

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 punctum (items b and e in the illustration below). 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.

The illustration below shows the following parts of the tear system or their location in the system. A: lacrimal or tear gland; B and E: lacrimal puncta; C and F: lacrimal ducts or canals; D lacrimal or tear sac; G: nasolacrimal duct or canal

Cystic Fibrosis or CF Facts

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. This results in reduced digestion of foods— especially carbohydrates and fats—and therefore reduced nutrient absorption.

People with cystic fibrosis often 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.

A significant part of each day in a CF patient's life is spent on treatments to clear the lungs. They take many pills a day. They periodically use oxygen inhalers and may wear a vibrating vest to break up mucus in the lungs. In addition, digestive enzymes are taken with all meals and snacks in order to obtain enough nutrients from food.

Cystic fibrosis results from a mutation in both copies of the gene for a protein called cystic fibrosis transmembrane conductance regulator, or CFTR.

Possible health problems associated with cystic fibrosis

Possible health problems associated with cystic fibrosis

Asthma Facts

Asthma is another problem that involves the production of more mucus than normal. People with the disorder have airways that 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. I have asthma, but the treatment prescribed by my doctor is a big help. Sometimes the condition is harder to manage, however. It may occasionally be a medical emergency.

Acute and Chronic 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 sometimes 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 lung damage.

COPD results in excessive mucus buildup and lung damage.

Chronic Obstructive Pulmonary Disease

Chronic bronchitis and emphysema are the two most common diseases classified as a chronic obstructive pulmonary disease or COPD. 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.

A wide range of treatments are available for the condition. The amount of help that they provide depends on multiple factors, including how bad the condition is when treatment begins. As is the case for many illnesses, it's beneficial to get an early diagnosis and to start treatment immediately.

A Friend and a Foe

Mucus is an essential substance in the human body and is usually a friend, despite its unpleasant reputation. Sometimes or in certain people, too much mucus is made and it’s 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.


This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

Questions & Answers

Question: If there is an insufficient amount of body fluid, do the mucous glands produce more secretions or none at all?

Answer: If a person is dehydrated, their body still produces mucus, but the mucus contains less water than usual. This means that it becomes thick and doesn’t flow very well, though the effect depends on the degree of dehydration. If drinking water doesn't solve the problem and the mucus stays thick and relatively immobile, a doctor should be visited.

Question: So many with Lyme disease suffer all of these problems, unfortunately. What's the best way to deal with all symptoms at once?

Answer: You need to consult a doctor in order to find the answer to your question, since I'm a science writer and not a physician. Lyme disease can be a complex condition with many symptoms. In addition, even when someone has been diagnosed with Lyme disease, problems with mucus may be caused by a different condition. A doctor should be able to diagnose the cause of the symptoms and prescribe a treatment that is beneficial for a particular patient.

© 2011 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on August 26, 2019:

You should ask your doctor this question, especially if you are concerned about a real-life situation. Some people have a mucous or mucoid cyst near a finger joint. This may be associated with osteoarthritis. The cyst is sometimes seen on a toe near a joint. Your doctor can offer you advice about these conditions.

FrankiE on August 26, 2019:

I was wondering is there any possibility thats known in a car crash of heavy impact that mucus can get in your bodies joints or any type of bone connection?

Linda Crampton (author) from British Columbia, Canada on May 31, 2019:

Thank you, Shiva. I appreciate your comment.

Shiva yadav on May 31, 2019:

it is very very helpful

Linda Crampton (author) from British Columbia, Canada on May 18, 2019:

You need to consult a doctor, Rambo. Only a physician can diagnose your specific problem.

Rambo on May 18, 2019:

Sometimes I used to caught alot by the problem of mucus and it comes out alot .. sometimes with chest pain . . What might be the reason for this.

Linda Crampton (author) from British Columbia, Canada on December 13, 2018:

I'm a science writer, not a doctor, so I can't answer your question. I'm puzzled by the idea that your cousin doesn't know which doctor to visit. She should visit a family doctor, general practitioner, or whatever a general doctor is known in your country. The doctor will make a diagnosis and if necessary may refer your cousin to a specialist. I hope she finds relief soon.

Asp on December 12, 2018:

Can a person experiencing regular, temporary stomach aches and diarreah are said to show ulcer symptoms? My cousin is experiencing them and unable to decide which doctor to consult as we don't know the problem. She eats balanced foods and stays well too. Can you suggest something? Thank you! :-)

Linda Crampton (author) from British Columbia, Canada on December 12, 2018:

I'm glad the article helped you learn about the mucus lining the stomach. It's very important that you see a doctor about your stomach pain, though. An ulcer or another problem in the stomach can't be self-diagnosed. Your doctor must give you a diagnosis and prescribe treatment.

sru on December 12, 2018:

hey! recently, I haven't been sleeping well due to the pain in my stomach. Think maybe ulcers based on symptoms( but I don't know why I would develop them). This article helped in learning abt lining and thank you!

Linda Crampton (author) from British Columbia, Canada on September 12, 2018:

Thanks for the visit and the comment, Mintu.

mintu on September 12, 2018:

very very helpful

Linda Crampton (author) from British Columbia, Canada on September 04, 2018:

Thank you very much for the comment and for sharing the interesting information, Susette!

Sustainable Sue from Altadena CA, USA on September 04, 2018:

Good article, Linda. Answered all my questions, even beyond the search term I used to find it ("healing properties of mucus"). Showed up on the first search page too!

Linda Crampton (author) from British Columbia, Canada on June 04, 2018:

You're welcome, Shristi.

Shristi on June 03, 2018:

Thanks for the information , Miss

Linda Crampton (author) from British Columbia, Canada on March 19, 2018:

I appreciate the comment, Ahmed. No, mucus and saliva are not the same thing. Saliva is a liquid made by the salivary glands. Saliva contains mucus, however, as well as other substances.

Ahmed on March 19, 2018:

Hey Miss Linda, I just finished reading your article and I have certainly found it interesting and useful for my science subject. By the way, I need to ask a quick question: are mucus and saliva the same thing?

Linda Crampton (author) from British Columbia, Canada on December 10, 2017:

Hi, Mangesh. We frequently swallow our mucus. In general, the acid and enzymes in the stomach destroy pathogens. If you'd like more information, you should consult your doctor.

Mangesh on December 07, 2017:

Please Miss Linda, can you tell me is there any easy and less expensive way to take excess mucus / phlegm out of throat, without spitting it out via mouth? I need help, I can't spit it, it feels so disgusting, but am scared about it! if I never take it out via mouth, will it cause health issues to me?

Linda Crampton (author) from British Columbia, Canada on November 30, 2017:

I think the disorder that you're interested in is bronchiectasis. Information about the disorder is available at major health sites on the Internet. For personal advice, though, you should visit a doctor.

Linda Crampton (author) from British Columbia, Canada on July 25, 2017:

Thank you, Simran. I appreciate your comment.

Simran on July 25, 2017:

Thanks for great information

Linda Crampton (author) from British Columbia, Canada on July 13, 2017:

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.

Linda Crampton (author) from British Columbia, Canada on May 31, 2017:

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

Faustina on May 31, 2017:

Can Epilepsy caused by Mucus

Linda Crampton (author) from British Columbia, Canada on May 17, 2017:

Thank you. I appreciate your comment.

Malar Vizhi Siddharthan on May 16, 2017:

Good article with in-depth information. Thanks for sharing

Linda Crampton (author) from British Columbia, Canada on March 02, 2017:

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

Mary Norton on March 02, 2017:

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

Linda Crampton (author) from British Columbia, Canada on July 17, 2014:

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

Biocurious World on July 17, 2014:

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

Linda Crampton (author) from British Columbia, Canada on March 12, 2012:

Thank you for the comment and the vote, Brinafr3sh!

Brinafr3sh from West Coast, United States on March 12, 2012:

Hi Alicia, Interesting hub, thanks. Voted up.

Linda Crampton (author) from British Columbia, Canada on March 08, 2012:

Thank you for the comment, Lucy.

Lucy on March 08, 2012:

I like your story. Very nice

Linda Crampton (author) from British Columbia, Canada on December 30, 2011:

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.

Demas W Jasper from Today's America and The World Beyond on December 30, 2011:

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.

Linda Crampton (author) from British Columbia, Canada on March 25, 2011:

Thank you very much, James.

James A Watkins from Chicago on March 25, 2011:

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

Linda Crampton (author) from British Columbia, Canada on March 16, 2011:

Thank you, michael hooper.

michael hooper on March 16, 2011:

thanks for info learnt a lot

Linda Crampton (author) from British Columbia, Canada on March 13, 2011:

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

GetSmart on March 13, 2011:

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

Linda Crampton (author) from British Columbia, Canada on February 27, 2011:

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.

Cindy Lawson from Guernsey (Channel Islands) on February 27, 2011:

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 on February 27, 2011:

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.

Linda Crampton (author) from British Columbia, Canada on February 05, 2011:

Thank you for the comment, CMHypno.

CMHypno from Other Side of the Sun on February 05, 2011:

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

Linda Crampton (author) from British Columbia, Canada on February 03, 2011:

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

prasetio30 from malang-indonesia on February 03, 2011:

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

Linda Crampton (author) from British Columbia, Canada on February 02, 2011:

Thank you for your comment, tnvrstar!

tnvrstar from doha, qatar on February 01, 2011:

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