[Zhihu question]
How can psychology explain the unusual habit of liking to eat boogers?
1. The normal explanation:
There is no profound reason for liking to eat boogers. It is simply because—
Boogers actually taste pretty good!
Boogers contain glycoproteins, salt, fat, and various other nutrients;
Boogers taste salty, with even a tiny hint of sweetness;
And the proportion of water in boogers is just right—not too much, not too little—giving them a pleasantly springy, chewy texture.
See? Whether you are talking about flavor or texture, boogers really are not hard to swallow!
What really needs explaining here is why many people have no psychological barrier to eating their own boogers, but feel disgusted at the thought of someone else eating boogers.
What is actually disgusting is not eating boogers, but seeing someone else eat boogers.
This is actually a kind of human “behavioral immune response.” A “behavioral immune response” is a series of behavioral instincts acquired by humans through evolution to avoid disease-causing microbes: whenever we observe cues associated with pathogenic microbes, we instinctively experience negative emotions and then try to get as far away from those pathogens as possible.
Humans have known about the existence of microbes for only a few hundred years at most, but this instinctive response to avoiding microbes was implanted in our genes long ago through the power of evolution.
The central emotion in the “behavioral immune response” is “disgust.” The things that make us feel disgusted are usually cues that pathogenic microbes may be present, such as other people’s bodily fluids.
Bodily fluids are ideal breeding grounds for all kinds of disease-causing microbes. In almost every situation, other people’s bodily fluids are disgusting. Seeing someone spit: disgusting. Seeing someone with pus running out of a wound: disgusting. Seeing someone eat boogers: of course disgusting too (really, just watching someone dig out a booger and fiddle with it is already disgusting).
Tears may be the only exception. Other people’s tears rarely trigger disgust, perhaps because visually they are completely indistinguishable from pure water.
Interestingly, other people’s bodily fluids are disgusting, while our own bodily fluids do not trigger a particularly strong sense of disgust (being excessively repulsed by our own bodily fluids would offer no evolutionary advantage whatsoever). But here is the interesting part: once there are strong cues suggesting that your own bodily fluid no longer belongs to you, you will find it disgusting too.
For example, does swallowing your saliva disgust you?
Not at all.
But what if you spit your saliva into a cup, leave it there for two minutes, and then pick it up and drink it? Does that disgust you?
Yes.
So eating your own boogers is not particularly disgusting; it is watching someone else pick their nose and eat boogers that disgusts us. This is simply an example of the human behavioral immune response.
2. A more imaginative explanation:
Here is another, more imaginative explanation.
Whenever we encounter an unusual fetish like this, evolutionary psychology is never content to sit quietly on the sidelines. Scott Napper, a biochemist at the University of Saskatchewan in Canada, proposed a hypothesis.
He believes that eating boogers may have an evolutionary benefit: training the immune system. Boogers and nasal mucus are the first line of defense against disease-causing microbes from outside the body, and they trap quite a few microbes. If you eat a booger, the microbes it contains can train the body’s immune system and help it develop resistance to those microbes. In fact, one study found that boogers contain salivary mucin, which may reduce the likelihood of tooth decay.
In plain English, people may like eating boogers because eating boogers might work a bit like getting vaccinated.
But a friendly reminder—
So far, there does not seem to be any direct experimental evidence proving the hypothesis above, so please eat boogers with caution!!
Written by: Zhichao Wei
References:
The composition of boogers, data from: www.ChemistryIsLife.com – The Chemistry of Boogers
Booger-eating and immunity: https://www.cbc.ca/news/canada/saskatchewan/picking-your-nose-and-eating-it-may-be-good-for-you-1.1387917
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