Nose picking

Nose picking is the act of extracting Mucus and nasal mucus with one's finger (rhinotillexis) and may include the subsequent ingestion of the extracted mucus (mucophagy). In Western cultures, this act is generally considered to be socially deviant; parents and pediatricians have historically tried to prevent development of the habit and attempt to break it if already established.

Prevalence
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 from Wisconsin USA 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.

In some cultures, nose picking is considered a private act akin to defecation, urination, flatulence, burping, or masturbation. Mucophagy, which is eating the extracted mucus, may be considered more taboo, and is sometimes portrayed in comedies.

Rhinotillexomania
When nose picking becomes a body-focused repetitive behavior or obsessive–compulsive disorder it is known as rhinotillexomania. Most cases do not meet this pathological threshold. When it does, however, treatments similar to other BFRBs can be employed, such as habit reversal training and decoupling.

Medical risks and benefits
The environment of the nose and the dried secretions removed contain many micro-organisms. When a person is contagious with a cold, flu or other virus, it is important that hands or other objects used to remove mucus are washed promptly because there is risk of introducing micro-organisms to other parts of the body or other people since it is a norm to shake hands in many societies.

Picking one's nose with dirty fingers or fingernails may increase risks of infection that may include an increase in the diversity of nose flora (and thus infection or illness), or occasional nosebleeds. One case of rhinotillexomania resulted in perforation of the nasal septum and self-induced ethmoidectomy. In children, the most common complication related to nose picking is epistaxis (nosebleed). Infections or perforation of the nasal septum are uncommon, but can occur. Nose picking, however, should not affect the sense of smell, as the nasal cavity where the olfactory nerves are located is too high up to reach.

Researchers at Griffith University have discovered a connection between bacteria and Alzheimer's disease. They have found evidence that a specific bacterium (Chlamydia pneumoniae) is capable of traveling through the olfactory nerve in the nose and entering the brain of mice. The intrusion of the bacteria is enhanced by nose picking. Once inside the brain, this bacterium triggers the production of certain markers that are indicative of Alzheimer's disease. Their study demonstrates that Chlamydia pneumoniae exploits the nerve pathway that extends from the nasal cavity to the brain as a means to invade the central nervous system. In response to this invasion, brain cells deposit a protein called amyloid beta, which is a characteristic feature of Alzheimer's disease. Activities like picking one's nose or plucking nasal hairs can damage the nasal lining, making it easier for bacteria to reach the brain. The olfactory nerve, located in the nose, provides a direct and relatively short route to the brain. Importantly, this route bypasses the protective barrier known as the blood-brain barrier. It seems that viruses and bacteria have identified this pathway as an easy way to gain access to the brain. Therefore, it is according to Professor St John, a co-author of the study, advisable to avoid nose picking or plucking nasal hairs to maintain the integrity of the nasal passage and lower the chances of developing Alzheimer's disease. However, there is still scarce evidence in favour of this claim, and most experts say it is too soon to link.

Some scientists claim 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". However, other scientists argue that, "because boogers are made from the same ingredients as the mucus we swallow every day, ... eating boogers doesn’t matter much to your immune system".

A study in the Netherlands published in 2023 found that healthcare workers who picked their nose were about three times more likely to contract COVID-19. The same study found no correlation between covid infection and nail-biting, or with wearing spectacles or having a beard, which could interfere with fit of protective equipment. The study was observational, finding a correlation without identifying a detailed cause.