Everyone has seen it. A child shoves one finger into his nostril, digs a nugget out of the cavity, pulls it out, and devours it like a delicious snack. It may be terrible for adults, but most kids don’t seem to be fazed by it at all. So why do kids eat boogers? And could they be eating something?
Most parents will tell you how common it is for children to eat their own mucus, a behavior known as “mucophagy,” but data on its prevalence are lacking.
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However, researchers found that mucophagy is common to at least 12 other primate species.
Evolutionary biologist Anne-Claire Fabre first discovered this while observing aye-ayes (Daubentonia madagascariensis). This lemur species is known for its 3-inch (8-centimeter) long middle finger, which it uses to pry insects out of hard-to-reach crevices. But when Fabre was observing an aye-aye captured in 2015, he was surprised to see its long, slender fingers stuck into its nostrils. Extract mucus. Then lick your fingers clean.
Fabre, an associate professor at the University of Bern in Switzerland, recalled, “I was both cheerful and disgusted at the same time.” “They seemed to be having a lot of fun. It’s something they do a lot.” (While it’s possible that captive aye-aye’s nose-picking habits were unusual, there’s no reason to think it wouldn’t also happen in the wild, Favre said.)
This led Fabre to wonder whether other primates also eat mucus. When she conducted a literature review that included her own observations about aye-ayes, she found evidence that gorillas, bonobos, chimpanzees, macaques, capuchin monkeys, and other primates also pick their noses and eat mucus. Most species used their fingers, but some used sticks to pry their loot open. Some primates even showed affection by picking other people’s noses, a study has found.
“If you look at the composition of mucus, it’s more than 98 percent water,” Fabre said. The rest is made up of proteins called mucins, carbohydrate components, and salt. It’s possible that animals derive some benefit from ingesting these components, Fabre explained, in the same way that some species eat their own feces and digest the remaining nutrients.
This idea raises the question whether there is a deeper evolutionary basis for mucophagy in humans.
Mucus creates a protective layer that traps dust, spores, and disease-causing microorganisms before they reach the lungs when we inhale. In 2013, a biochemist proposed the hypothesis that eating boogers could expose children to small amounts of pathogens that could train the immune system to identify these molecules and trigger an immune response. However, this idea was never conclusively tested in empirical research.
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Dr. Chittaranjan Andrade, author of a 2001 nose-picking study of teenagers, is wary of such theories. “I’m a skeptic. The immune substances that survive drying in mucus are likely to be very small in quantity, and are likely to be digested after ingestion,” so the effectiveness is likely to be limited, the senior emeritus professor at the National Institute of Mental Health and Neurosciences in Bangalore, India, explained in an email.
Other experts warn that children’s nose picking and mucophagia should be controlled if they are around someone who is immunocompromised, as runny noses can spread pneumonia-causing bacteria.
Although there is no evidence to support the idea that mucophagy boosts immunity, researchers have been looking for more intuitive reasons why children eat their own mucus. Boogers can cause nasal itching, pressure, and discomfort, which can prompt nose-picking, Fabre speculates, and curious children may do taste tests.
One researcher directly asked children why they ate boogers. The results were published in a book chapter published in 2009, but were not peer-reviewed and were based on a very small sample of just 10 children. But their insights included the fact that people like to eat boogers simply because of their appealing texture and taste.
Andrade believes children pick up this habit because they don’t yet have the negative associations it has with older adults. “because [children] If you do it openly, you will be observed and reprimanded, and the act of picking as well as eating will be condemned, so I guess they won’t do it again, not openly anyway,” Andrade said.
Until more concrete research is done on this question, the exact answer to why children eat boogers will remain unknown. At least for Fabre, it’s a topic that requires further research to understand whether mucophagy may benefit or harm a child’s development.
After all, she believes that she may take her children’s words to heart and eat boogers simply because she likes them. “It’s crunchy and a little salty,” she says. After spending hours observing aye-ayes picking their noses and learning that the habit is widespread in other species, Fabre no longer feels disgusted. “Honestly, in my opinion, it’s not disgusting.”
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