A person might think that their body only makes mucus in response to illness, allergens, or irritants. But the body is always producing mucus, which is crucial for the functioning of several organs and the immune system.

Many health issues can lead to a buildup of mucus, drawing a person’s attention to this key bodily fluid. Most healthy people never notice that they are continually producing and swallowing it.

Below, learn what mucus is, how it forms, and what causes a buildup. We also explore tips for clearing it and when to contact a doctor.

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Mucus is a fluid that the body produces to line moist areas, such as the:

  • eyes
  • mouth
  • nose
  • sinuses
  • lungs
  • throat
  • stomach
  • intestines
  • reproductive organs

Most people only notice mucus when they are ill or exposed to allergens or irritants in the air. But glands in the areas listed above make mucus continually, secreting around 1–2 quarts daily.

Mucus helps with crucial functions, such as:

  • adding moisture to inhaled air
  • preventing moist organs from drying out
  • filtering, trapping, and eliminating inhaled microparticles or microorganisms, such as allergens, dust, smoke, pollution, viruses, bacteria, and fungi
  • fighting infection

Mucus helps trap microorganisms and microparticles on the surface of the lungs. Tiny hair-like appendages that line the lungs, called cilia, then beat in unison, creating a pulse that moves the entrapped particles up and out of the lungs.

Once the particle-filled mucus reaches the back of the throat, it typically moves down the throat without the person noticing.

After traveling down the throat, the mucus reaches the stomach, where it is digested and eliminated from the body in feces or urine. Mucus in the throat can also be coughed up and spit out.

Mucus is mostly made of water, but it also contains important proteins and sugars. The cells that make mucus also produce molecules that support immune function, and these become incorporated into the mucus.

The molecules in mucus include:

  • antimicrobial molecules
  • immune-modulating molecules
  • protective molecules

The tissues lining the airways, nose, sinuses, and mouth contain two primary cell types: secretory cells, which release the components of mucus, and ciliated cells. These are covered with tiny hair-like projections called cilia.

Mucus is mostly water and a gel-forming molecule called mucin.

Special secretory cells called goblet cells are the predominant producers and releasers of mucin. A goblet cell is shaped like a medieval goblet, and it is not covered with cilia.

Goblet cells and other secretory cells also release a range of proteins, salts, fats, and immune molecules that mix with mucin and are incorporated into mucus.

Submucosal glands, found in the airways, mouth, and gastrointestinal tract, also produce and release mucin and mucus.

Ciliated cells use their tiny projections to move mucus throughout the body. The cilia move in a way that creates a unified pulse, pushing mucus along in waves.

Infections and irritants

When the airways are exposed to irritants, goblet cells and submucosal glands produce extra mucus to clear the airways.

In addition, infections can cause inflammation in airway tissues, which can likewise trigger the submucosal glands to produce more mucus. During an infection, mucus thickens because it fills with immune cells and entrapped foreign particles.

Allergic reactions occur when the immune system responds excessively to a harmless substance. The reaction triggers the release of histamine — a compound that can cause the airway linings to swell and stimulate the submucosal glands to produce more mucus.

Most healthy people are unaware that they are continually producing and swallowing mucus.

Several health issues can cause mucus to build up, either by stimulating excessive production, blocking or reducing mucus elimination, or causing the mucus to thicken.

Factors associated with mucus buildups include:

  • allergies, especially to dairy
  • bacterial, viral, or fungal infections
  • breathing in very cold or dry air
  • inhaling irritating particles such as pollution, smoke, dust, dander, or mold spores
  • hormonal changes that occur with aging
  • certain medications that can thicken mucus, including birth control pills and high blood pressure medications
  • gastroesophageal reflux
  • pregnancy
  • asthma
  • vasomotor rhinitis, having an extra-sensitive nose
  • nasal growth or polyps
  • irregular nasal cartilage structure
  • cystic fibrosis
  • non–cystic fibrosis bronchiectasis and panbronchiolitis
  • chronic obstructive pulmonary disease, commonly called COPD
  • primary ciliary dyskinesia
  • hypogammaglobulinemia
  • HIV
  • organ transplantation
  • blood cancers
  • issues that disrupt the mechanics of the lungs, such as paralysis, intubation, surgery, or immobilization

The best way to clear a buildup depends on the underlying cause and contributing factors.

Common home care strategies include:

  • using an over-the-counter (OTC) saline nasal spray
  • taking OTC nondrowsy decongestants or antihistamines
  • rubbing a product that contains eucalyptus oil on the chest and throat or inhaling it
  • avoiding all allergens, including those in foods
  • gently pounding or tapping on the back and chest repeatedly to loosen the mucus
  • adding humidity to the air — using a humidifier or taking a warm shower or bath
  • applying a warm, moist washcloth over the face
  • covering the nose with a scarf in cold weather
  • not smoking and avoiding secondhand smoke

Many natural products can reduce mucus buildups or treat the respiratory conditions that cause them. Natural remedies with some scientific backing include:

Learn more about how to clear mucus here.

If a buildup of mucus is severe or persistent, it can lead to:

  • dehydration
  • postnasal drip
  • a sore throat
  • sinus or nasal pain or pressure
  • jaw pain
  • dry mouth
  • a cough
  • lung, nasal, sinus, or throat infections
  • digestive problems
  • weight loss
  • trouble breathing
  • reduced oxygen levels and increased circulating carbon dioxide levels
  • atelectasis, in which the lungs cannot fully expand or collapse
  • respiratory failure
  • heart failure

When excessive mucus production or buildups happen with no clear cause, contact a healthcare provider.

Also seek professional care if mucus:

  • is very thick
  • has a color — healthy mucus is clear
  • interferes with breathing
  • does not respond to home treatment
  • lasts longer than a week or two

Also, talk to a doctor if troublesome mucus occurs with:

  • a fever or chills
  • unexplained exhaustion
  • trouble sleeping
  • wheezing or noisy breathing
  • breathing changes, such as rapid, shallow breathing or shortness of breath
  • a lack of appetite or weight loss
  • chest pain or pain when breathing
  • pus or blood
  • a cough
  • nausea and vomiting
  • acid reflux
  • a severe sore throat
  • rash on the chest, throat, or neck
  • bluish or pale coloring of the skin, especially around the fingers, toes, and lips
  • swelling of the throat, neck, head, feet, or ankles
  • confusion or other changes in mental functioning or state

Mucus is key to the functioning of vital organs and the immune system, so the body is continually producing it.

Several health issues can lead to a buildup of mucus or cause the body to produce excess. This can lead to complications.

Usually, OTC products and home care techniques can clear excess mucus. Contact a doctor if a mucus buildup has no clear cause, does not resolve with home care, or occurs alongside any other concerning symptoms.