Lining tissues in the body produce a substance that is slippery and stringy called mucus. The body produces about 1 to 1.5 liters a day to provide many different functions such as moisturizing, lubricating, trapping foreign substances, etc. It is known for protecting and cleansing passageways throughout the body. Mucus, however, can be a factor in many sicknesses relating to the respiratory system such as asthma and bronchitis. Because of this, mucus has a negative reputation even though God made it for a reason that many people take for granted. 
Made of water and different proteins such as mucins, antibodies, antiseptics, and salts, mucus is produced all throughout the body. Mucus is mostly found in the eyes, nose, mouth, throat, lungs, respiratory tract, digestive tract, and reproductive tract. This is all thanks to mucous membranes, also known as mucosa. Some mucous membranes secrete mucus, keeping the surface of the passageways moist. In the eyes, there are mucous membranes over the white parts of the eye, producing mucus. This mucus is thinner than most and is an ingredient in tears. These tears drain through the nose when sleeping, and in the process form into "eye gunk." In the respiratory system, the mucus catches any debris in the air on its way to the lungs such as bacteria and dust. The mucus prevents anything larger than five microns from getting into the lungs.  In the digestive system, mucus is used as a lubricant for the food traveling down from the mouth to the stomach. Starting at the mouth, the mucus helps to dissolve the food, softens it, and acts as a lubricant when swallowing it. In the stomach, hydrochloric acid and pepsinogen are produced to digest proteins. The mucus flows between the lining of the stomach and the hydrochloric acid and pepsinogen to prevent the stomach from digesting itself. After the food is processed into bile, the mucus is, once again, needed in the digestive tract. The mucus serves as a barrier between the intestinal lining and the bile to prevent inflammation and infection in the intestines.  In the reproductive system, females have an organ connecting the uterus to the vagina called the cervix. The cervix has a canal inside which produces mucus. Female hormones control the production of this mucus called cervical mucus, which is made up of mostly water. The main functions of the cervical fluid are to lubricate the vagina and to prevent infection. Many women use cervical fluid to learn more about their fertility and ovulation.  
Mucus needs to be continously transported to the oropharynx in order to function properly. Cilia, small microtubules that are coated in plasma membrane, are rods that have claws at the end. In the respiratory system, they also protect the passageway from debris and provide locomotion for the mucus. While cilia beat in a pattern continuously, it pushes the mucus towards its destination. The cilia also create friction, making it easier for the mucus to travel. Mucus also travels based off of how forced one's breathing may be. Because the airways are compressed during forced expiration, the velocity of the of the air flow increases. This makes traveling of mucus faster. However, diseases such as asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis, and a dysfunctional cough or glottic control may have irregular mucus movement. With asthma, ciliary activity are reduced, slowing down the locomotion of movement. They are even slower when a person with asthma sleeps. Patients with chronic obstructive pulmonary disease have the same issue except the ciliary epithelium deteriorates. This reduces the movement of mucus even more than someone with asthma. In cystic fibrosis, mucus is known to interfere with the airways, worsening the locomotion and the disease as well. When mucus cannot sufficiently transport, it can lead to infections. 
One a person has cystic fibrosis, the mucus in their body is sticker, thicker, and overproduced. It sits in the passageways, and because of its texture, it is unable to move at a regular pace. With all the bacteria it collects protecting the respiratory system, an infections comes from the bacteria in the mucus. Because of this, mucus often blocks digestive enzymes from reaching the small intesine which prevents the body from digesting the carbohydrates and fats. The lack of digestion prevents the body from getting the ideal amount of nutrients. Cystic fibrosis is a genetic disorder, and researchers still look for a cure. However, even though the lifespan of a cystic fibrosis patient is shorter, it improves as the treatments for the disease improve.
Asthma Asthma patients also experience an overproduction of mucus in their respiratory system. An asthma attack is triggered because the passageways are irritated by a particular substance or exercise. During an asthma attack, the passageways are inflamed and swollen, while mucus overproduces. This makes it difficult to breathe, as the mucus blocks what is left of the passageway. Although there is no cure for asthma, the elimination of asthma attacks are possible with the help of a doctor.
Bronchitis, another disese related to the overproduction of mucus, is similar to asthma. The passageways for the respiratory system become inflamed and swollen like asthma. However, bronchitis can be acute or chronic. Acute bronchitis is normally just an infection and is only temporary. Chronic bronchitis is usually permanent, however. It is caused by smoking or the inhalation of certain substances. When suffering from bronchitis, a patient usually experiences color change in their mucus from clear to yellow or green caused by the infection.
Chronic Obstructive Pulmonary Disease (COPD)
Chronic bronchitis is a form of chronic obstructive pulmonary disease. Along with emphysema, they are the most common diseases among the COPD classification. Both chronic bronchitis and emphysema are caused by smoking or the inhalation of a chemical substance. Those who suffer from emphysema also experience trouble with exhalation as oxygen is absorbed into the blood. When their conditions worsen, the patients normally wheeze and cough up mucus. This is damaging to the lung, but seeing a doctor can improve these conditions. 
More detail about the benefits of mucus
- Stöppler, Melissa Conrad What is Mucus MedicineNet. Web. Updated August 30, 2018.
- Lechtzin, Noah Defense Mechanisms of the Respiratory System Merck Manuals. Web. Accessed May 19, 2019
- Hansson, Gunnar Role of mucus layers in gut infection and inflammation NCBI. Web. Published December 14, 2019.
- Escoffery, Liz What’s cervical mucus? Natural Womanhood. Web. Posted June 11, 2016.
- Villines, Zawn What to know about cervical mucus and fertile discharge Medical News Today. Web. Reviewed October 29, 2018.
- van der Schans, Cees Bronchial Mucus Transport RC Journal. Web. Accessed May 20, 2019.
- Crampton, Linda Mucus in the Human Body: Functions and Health Problems Owlcation. Web. Updated May 1, 2018.