[1] In Western cultures, this act is generally considered to be socially deviant;[2] parents and pediatricians have historically tried to prevent development of the habit and attempt to break it if already established.

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.

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.

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.

[1] 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".

[1][20] 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".

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.