There’s an old joke: What’s the difference between broccoli and boogers? You can’t get kids to eat broccoli.
There definitely seems to be something about boogers that is simply irresistible to many children. Glance at a group of five or more children, and chances are good that at least one of them will likely have their finger either thrust up their bulging nostril halfway to their brain or poking the flake/chunk/globule sourced from within said nostril into their mouths. Yes, children can be truly disgusting.
Boogers, of course, form in the nose, when some of the mucus that is constantly produced gets dried out. The purpose of nasal mucus is to stop potentially harmful particles and pathogens found within the air from being inhaled. Instead, they are caught by wet, sticky snot and taken down the throat to be dealt with in the stomach. Larger particles, or large amounts of them, can form bigger sticky chunks or linger long enough to dry out, which is when the stuff in your nose goes from sniffable to pickable.
Mucophagy, According to Science
Aside from being gross, the act of picking one's nose itself is fairly inadvisable as a probing finger can introduce all sorts of infectious materials into the body, as well as pass illnesses onto other people. Picking your nose then shaking hands with someone, for example, is one way to spread pneumonia. You can also damage the inside of your nose, which can cause nosebleeds.
As for the booger-eating—or, to use its more elegant name, mucophagy—opinions differ, health-wise. In 2013 Scott Napper, an associate professor of biochemistry at the University of Saskatchewan in Canada, sparked headlines around the world when he proposed a theory that evolution might suggest that eating boogers is one way to boost your immune system, and that boogers’ deliciousness was an advantageous mutation. He suggested that by ingesting these particles rather than blowing them out (or wiping them under a school desk), children were increasing their immunity, via exposure, to any illnesses they could cause.
However, as other scientists have pointed out, the majority of the mucus you produce gets swallowed anyway, so the small percentage of it that makes a brief journey outside before being chomped is unlikely to add many health benefits to the proceedings.
Just for the Taste of It
A more pointed answer to the question of why kids eat their boogers is just because they like the taste. Tastiness is key to Napper’s theory—and a frequently-cited 1966 look into derivatives of coprophagia (the eating of poop) by psychiatrist Sidney Tarachow states [PDF]: “The patients enjoy these activities. The nose pickings are reported to be quite tasty, salty, to be exact.”
The convenience of boogers also cannot be overstated. How delicious does something even need to be when it’s so handily located near one’s mouth? Perhaps, ultimately, the answer to why kids eat boogers is the same as that given by the great mountaineer George Mallory, when he was quizzed as to why he was trying to climb Mount Everest: “Because it’s there.”
Maybe that’s it, or maybe … it’s snot.