Rhinotillexomania

Nose-picking is the act of extracting nasal mucus with one's finger (rhinotillexis) and may include the succeeding action of ingesting the mucus picked from the nose (mucophagy). This action is condemned in most cultures; societies try to prevent development of the habit and attempt to break it if already established. Mucophagy is a source of mockery and entertainment in the media.

However, some scientists argue that mucophagy provides benefits for the human body. Friedrich Bischinger, an Austrian doctor specializing in lungs, advocates using fingers to pick nasal mucus and then ingesting it, stating that people who do so get "a natural boost to their immune system." The mucus contains a "cocktail of antiseptic enzymes that kill or weaken many of the bacteria that become entangled in it", so reintroducing the "crippled" microorganisms "may afford the immune system an opportunity to produce antibodies in relative safety."

Nose-picking is an extremely widespread habit: some surveys indicate that it is almost universal, with people picking their nose on average about four times a day. A 1995 study of nose-picking, requesting information from 1,000 randomly selected adults, gathered 254 responses. It defined nose-picking as "the insertion of a finger (or other object) into the nose with the intention of removing dried nasal secretions". Of those who responded, 91% said they were current nose-pickers (but only 75% of these believed everyone did it), and two respondents claimed to spend between 15 and 30 minutes and between one and two hours a day picking their noses.

Mucous membranes in the nasal cavity constantly produce a wet mucus that removes dust and pathogens from the air flowing through the cavity. For the most part, the cilia that also line the cavity work to move the mucus toward the throat, where it can be swallowed. However, not all the mucus stays fluid enough to be moved by the cilia. The closer the mucus is to the nostril opening, the more moisture it loses to the outside air, and the more likely it is to dry out and become stuck. Once dried, the mucus typically causes a sensation of irritation that leads to the compulsion to dislodge the itch by picking. Other reasons to remove excess dried mucus include impaired breathing through the nose and a concern that it may be visible to others in the nostril openings.

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Wikipedia