Mucus in the Human Body

Mucus is a slippery liquid made by mucous membranes. These membranes line the passageways inside our bodies that connect to the outside environment, including the nose, the mouth, the respiratory passages, the digestive tract and the reproductive tract. Mucus may destroy bacteria and viruses, trap particles such as dirt, prevent water loss, humidify a passageway, lubricate the movement of materials or protect surfaces from damaging substances.

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

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 and its contents up to the back of the throat, where the mucus may be swallowed or released into the nose. Smoking can damage the cilia, resulting in a build-up of mucus in the respiratory tract.

Saliva in the mouth contains mucus, which is an excellent lubricant and makes it easier to swallow food.

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, which 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 is thinned or removed, which may happen during a stomach 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.

Glands in the lining of the small intestine and the large intestine also produce mucus. There is generally some mucus in stool, but usually not enough to be noticed. Noticeable amounts of mucus 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.

The cervix is the lower end of the uterus and produces 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 prevent infection and supports or inhibits sperm movement.

After menstruation, there is usually very little cervical mucus made. As the cycle progresses, the amount of mucus produced 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 cervical mucus is most abundant, but 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.

The conjunctiva is a mucous membrane that covers the white part of the eye (the sclera) and the inside of the eyelid. The conjunctiva produces a thin mucus that lubricates the eye, as well as some tears, although most tears are produced in the lacrimal glands. Once mucus and tears have spread over the surface of the eye they drain into the nose. Some people wake up in the morning with dried particles of mucus in the corner of their eyes.

Mucus may be colorless, white, gray, yellow, green, brown, black, orange, pink, red or a rust color.

Gray Mucus

Mucus cleared from the nose is often gray in color due to the trapped dust and dirt that it contains.

Yellow or Green Mucus

Infections can produce yellow or green mucus. People suffering from bronchitis caused by a viral infection may produce mucus of these colors in their airways. Mucus coughed up from the respiratory system is sometime called phlegm. Sputum is phlegm mixed with saliva.

The sinuses are hollow spaces in the facial bones. Sinuses are lined with mucous membrane. A sinus infection, called sinusitis, involves inflammation of the sinus lining. During a sinus infection, the mucus produced in the sinus may be green or yellow-green and is discharged through the nose or into the throat through post-nasal drip.

Brown or Black Mucus

Brown mucus can be produced by an infection. Tars obtained from cigarette smoke can stain mucus in the respiratory system brown or black. Coal miners may develop black mucus too due to the inhalation of coal dust.

Orange, Red or Rust Colored Mucus

People with pneumonia may produce orange mucus in their respiratory systems. Pink, red or rust colored mucus indicates the presence of blood.

Cystic Fibrosis

Cystic fibrosis is a genetic disorder in which the body makes mucus that is much thicker and stickier than normal mucus. The thick mucus cannot move easily and collects in body passages. Mucus in the breathing tubes makes it difficult to breathe and frequently leads to bacterial infections. In cystic fibrosis, mucus also 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.

Asthma

People with asthma have airways which are sensitive to allergens or irritants such as house dust, 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.

Bronchitis

Bronchitis also involves inflammation of the airways and excess mucus production. Acute bronchitis is generally caused by a virus infection, while chronic bronchitis usually results from smoking or chronic inhalation of certain chemicals or pollutants.

Mucus is an essential substance in the human body. However, at times, or in certain people, too much mucus is made and the mucus is transformed from a useful material into a dangerous one. Hopefully medical research will continue to discover improved ways of dealing with excess mucus and its consequences.