Mucus in the human body serves many vital functions. Most importantly, mucus protects the body from harmful substances by acting as a barrier and by facilitating the removal of such substances. The presence of thick mucus is often an indication that the body is fighting infection, trying to rid the body of harmful substances or responding to the ingestion of certain foods.
For animals in the vertebrate phylum, mucus is produced by mucous membranes that are located in various places within the body of the animal. In humans, mucous membranes are located on cavities of the body that come into contact with the outside world. These include the nostrils, mouth, ears and genitals.
Mucus is made of water, carbohydrates, proteins, cells and salt, and it serves many important functions for the human body. Mucus protects organs by acting as a barrier that prevents any foreign matter from making its way into the body. For example, mucus in the nasal cavity traps allergens and dust particles before they can make their way into the lungs. This helps prevent humans from inflammation or infection that can be caused by common irritants such as smoke, mold and many bacteria and viruses.
In carrying out its protective function, mucus also removes harmful particles. Thus, when the mucous membranes come into contact with an infectious agent such as a bacteria or virus, they begin to increase mucus production to increase the efficiency of removal. This results in the production of thick mucus. For instance, when the nose is infected with the common cold virus, the nasal and sinus membranes increase the production of mucus in order to remove the virus from the body, thus resulting in the thick nasal mucus commonly experienced during a cold.
The same phenomena takes place when the body comes into contact with an allergen. For many people who suffer from allergies, the presence of the trigger allergen on their mucus membranes causes an increase in the production of mucus, resulting in thick mucus meant to eradicate the pollutant from the body. Increased mucus production can occur in any part of the body that has mucous membranes and comes into contact with an allergen.
In some people, thick mucus can be the result of a food sensitivity or allergy. This is often the case with dairy products. Many times, the fat in dairy products increases the viscosity of mucus, and some people notice an increased amount of thick mucus in their nasal passages and lungs shortly after consuming these foods.