¶ 2006-01-18 16:59:00 +0000
The nose is the only organ of the body that for the most part does not have a self-cleaning mechanism. The purpose of the mucous is believed to be (among other things) the entrapment of bacteria and other undesirables that would otherwise have entered the body.
By picking, we provide the nasal passages with a method of cleaning to provide new mucous and by – ugh – eating we introduce the bacteria into our systems that were otherwise trapped, thus allowing our immune systems to learn about it and, more importantly, learn to defeat it. [source]