The Secrets of Bellybutton Fuzz’

From Here’s Why Some People Have More Bellybutton Lint Than Others:

After conducting a widespread survey, he concluded that navel fluff is driven by stomach hair, which collects lint from clothing and puts it on a one-way path to the bellybutton.

Another mystery solved. Been wondering that for quite some time. There are some more interesting links in the article as well.